What is it called when auto-ranging is used with a digital meter and a voltage is displayed before coming into contact with the circuit? PP17
How can this be eliminated in most meters?
ghost voltage
By selecting the manual setting
source: test instruments NJATC 2008
What are the accuracy ranges of analog and digital testing meters for voltage? PP18
analog = 1-5%
digital = .01-1.5%
source: test instruments NJATC 2008
Whenever possible, the test leads of a meter should be connected to which side of a fuse or breaker and why? PP20
load side, to provide better short circuit protection.
source: test instruments NJATC 2008
The primary contributing factor to arc blasts is what and is caused by what?
transient over voltages, caused by high current loads being switched off, or by lighting strikes nearby.
Source: PP25 test instruments NJATC 2008
With an IEC 1010 measurement category of Cat II (1 phase receptacle connected loads), outlets at more than how many feet from a Cat III source and Cat IV source become Cat II? PP26 test instruments NJATC 2008
outlets at more than 30' from Cat III or 60' from a Cat IV source become Cat II.
source: test instruments NJATC 2008
What is magnetic field coupling also referred to as?
Also known as noise, and is mutual induction between 2 signal wires.
PP18 test instruments NJATC 2008
A temperaturedifference in any enclosure, or metalic part of an electrical system is considered a light load, heavy load, and a maintance issue at how many degrees F?
Light load= 40F
Heavy load = 60F
Routine maintenance required = 85F
PP18 test instruments NJATC 2008 PP40
PP40 test instruments NJATC 2008
If a test instrument has a red and green condition indication rather than black (common) and red (hot) then this is considered what?
Red = high voltage
Green = low voltage
PP41 test instruments NJATC 2008
In what order should leads on a DMM always be applied to an energized circuit and why? PP 42
Black (common) applied 1st
Red (hot) applied 2nd
Because Red first can cause an energized circuit with the electrician in series with the ground by holding the black lead
Discharge on a test instrument is represented by what symbol? PP 42
The diode symbol
The formula for Peak, Effective, Average, and Peak to Peak voltages in an AC sine wave are? PP44
Peak = 1.414(RMS/eff) a.k.a. max instantaneous value
Effective (RMS) = .707(peak)
Average = .637(peak)
Peak to Peak = 2(peak)
What is it called when auto-ranging as used with a digital meter and a voltage is displayed before coming into contact with the circuit?
ghost voltage.
JATC test instruments 20008 PP17
How can ghost voltage be eliminated in most meters?
ghost voltage. By selecting the manual setting
Whenever possible, the test leads of a meter should be connected to which side of a fuse or breaker and why?
load side, to provide better short circuit protection is the preferred method to connect these.
NJATC test instruments 2008 PP.20
What should always be worn with rubber insulating gloves? pp22
Rubber gloves should always be laboratory tested at what interval? pp22
leather protectors (gloves)
every 6 months at minimum
What is the purpose of a static transfer switch?
Static transfer switches (STS) are such electrical devices which are used for very fast switching between electrical power sources. They perform instantaneous switching operations and thus supply immediate power to the load.
what is the most common voltage for an RPP or reactor power panel to the rack bus and data racks? why? -At Looking Glass
480 volts. use of the highest voltage in an acceptable range allows the I2R watt losses for heat to be lowered and increases efficiency in the data center.
There are 4 IEC1010 measurement categories, from low to high voltage, what are they and what system types do they apply to? PP26 test instruments NJATC 2008
phase 4 is closest to the utility
Cat I: electronic; any high-voltage, low energy source derived from a high-winding-resistance transformer, such as the high-voltage section of a copier
Cat II: 1 phase receptacle connected loads
Cat III: 3 phase distribution, including 1 phase commercial lighting
Cat IV: 3 phase at utility connections, or any outdoor conductors
How do you test the leads on a DMM prior to an ohmic reading, and what are the desired results? PP37 test instruments NJATC 2008
The DMM must first be zeroed and then the leads should be touched together for an ohmic reading of less than 1
When the conductor is straight, the flux lines cut through only one of the conductors, but when the conductor is ______ the flux lines cut through inductor at more than one point. This increases the CEMF by self induction.
Coiled. When the conductor is coiled it allows more points at which the lines of flux can cross the conductor and increase this.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP76
Because an iron core provides an easy path for magnetic flux, windings ______ cores produce greater self-inductance windings with an air core.
with soft iron windings produce this.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP76
Longer cores result in? And what happens when core length is doubled?
fewer flux lines are the result of this.
This results in reduced inductance. If the core length is doubled, the CEMF decreases by 50%.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP76
When the applied voltage is at its maximum in one direction, the induced voltage is at its maximum in what way?
This is at its maximum in the opposite direction. Remember: CEMF is 180° out of phase with the applied voltage.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP77
An electrical source with many motors and inductive loads tends to have a high amount of inductive reactance and a low power factor.
Adding capacitors will help counteract high inductance and increase the power factor. This will help with the problem of this type of load.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP77
Circuits and equipment must be sized to the circuit ____(I2R, E2/R, or IxE)____ loads?
VA is what this must be sized to. Or apparent power and expressed by IxE. In a DC circuit, however it is IxExPF in an AC single phase circuit and IxEx1.73 (√3) in a 3 phase AC circuit.
If you measure voltage and current in an inductive or capacitive circuit and multiply them together, the product is the apparent power supplied to the circuit by the source.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation
, based on the 2014 PP79
To determine the true power, or watts, consumed by a DC versus AC circuit, what formula must be used? This is not apparent power.
DC power= IxE
AC power(watts)= IxExPF (PF=R/Z or True power/ apparent power (I2R/IE).
These two formulas determine this type of power consumed by the circuit. It is important to note the watt loss or I2R is not used.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP79
Alternating-current inductive or capacitive reactive loads cause the voltage and current sine waves to be out-of-phase with each other. power factor measures what in regards to the wave form?
This measures how far the current waveform is out-of-phase the voltage waveform.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP80
What condition is called “unity power factor” in a purely resistive circuit?
Unity power factor is when the power factor is at 100% in a this type of circuit.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP79
Why are circuits and equipment sized per the VA available to the load?
remember: the output watts of a generator are larger than the VA demand... instead think of this as VA and KW at the load.
Apparent power (VA) is used for sizing circuits and equipment. Because the VA of the load isgreater than the watts of the load, fewer loads can be supplied by each branch circuit. More circuits and panels, and larger transformers may be required. This is why these are sized per this.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP82
Transformers are always sized based on what rating?
What is the formula for this?
KVA (apparent power) is always the rating for these, not KW because they are an inductive load which results in apparent power. Apparent power is measured in kVA, while KW is used only for true power such as resistive loads.
Apparent power = KW/PF so…
kVA= IxE/1000 for KVA would not account for power factor and would be wrong as mentioned on page 19 of Master Electrician: 2014 Exam Questions & Study Guide. Ray Holder
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP82
In an AC circuit. What does it mean regarding current and a low power factor?
This AC circuit draws more current when this power factor is lower.
individual conductors shall be insulated or covered. What is the exception? Considering a grounded conductor.
The grounded conductor of a multi conductor cable shall be permitted to be bare. NEC 230.22 exc.
the difference between a neutral and a grounded circuit conductor is?
only a neutral carries unbalanced current
in the NEC handbook under Article 200. 1 it states "the grounded conductor is often, but not always, the neutral conductor. As defined in Article 100, a neutral conductor is one that is connected to the neutral point of an electrical system. In a single phase, 2 wire or 3 phase, corner grounded Delta system, the intentionally grounded conductor is not a neutral conductor, because it is not connected to a system nuetral point.
power factor is ______ _________ of current and voltage in an AC circuit?
phase displacement. Source: Journeyman Electrician exam questions and answers, Tom Henry 2011. Also it is the formula/ratio of TP/AP (true power to apparent power and R/Z (Resistance to impedance. The angle theta in a voltage or impedance triangle as well.
hysteresis is?
the lagging of magnetism, in a magnetic metal, behind the magnetizing flux which produces it.
the Wheatstone bridge method is used for accurate measurements of?
Resistance
when a circuit breaker is in the open position do you have a short in the grounded or the ungrounded conductor?
either. However, if the question poses an ungrounded Delta system then it would not include the neutral and this is how Europe does things. The Wye system is rarely common. Remember also a neutral carries unbalanced load and a grounded conductor does not. Tom Henry’s 2011 Journeyman Electrician exam questions and answers pp 21
wire connectors are generally classified as what type? Thermal or pressure?
both.
voltage of a circuit is best defined as?
the effective difference of potential between two conductors. Also represented by .707(Peak voltage)
When calculating a single motor’s wire size you find the FLC (full load current) wire size in the ampacity tables 310.15(B)2(6) in 2015, is this the wire size?
At what voltage does part 2 of art 430 apply?
No. An adjustment factor of 125 percent must be applied for a continuous DUTY motor. NEC 430.22 or art 430 part 2.
part 2 (motor circuit conductors) of art 430 shall not apply to motor circuits over 1000 NOMINAL volts. (Nor does part 3: Motor and branch circuit overload protection)
please note that in the 2017 handbook it states in the informational section part 3 art. 430(A)1 that a continuous duty motor is not the same as a continuous load. As defined in art 100 by the termduty.
what is the difference between the terms continuous duty and continuous load in NEC art 100 definitions?
Continuous duty and continuous load are not the same. Duty refers to operation at a substantially constant load for an indefinitely long time. Whereas, load is for maximum current for 3 hours or more.
What is the current drawn when PF is .91? This question requires what mathematical formula?
watts ⁄pf x voltage
What must be remembered when using the lighting load demand factors, table 220.42 when calculating the total number of branch circuits for illumination?
That table 220.42 “lighting load demand factors” shall not be used in determining the number of branch circuits.
The amperage in a dual voltage motor will be ______ if the voltage is doubled despite ohm’s law finding I using R.
Example question: A dual-voltage three-phase motor draws a current of 45 amperes when connected to a 240 volt, three phase circuit. How much current will the same motor draw if connected to a 480 volt three-phase circuit? Source: Electrician’s exam preparation guide, Dale C. Brickner, 2011: PP 48
halfed. Remember that a dual voltage motor will have the winding in series for high voltage and parallel for low voltage.
What formula is used to find ‘R’ (resistance) in a length of wire? You will need to know the specific resistance for copper and aluminum. What are they?
R=(K×L)∕CM ;where CM is circular mils, K is specific resistance of 12.9 for copper and 21.2 for Aluminum, and L is length. Notice the 2kli/cm would be a voltage drop calculation for single phase.
Motor branch circuits and feeders ocpd is rounded up or down?
Motor branch circuits are rounded up and feeders are rounded down.
What is the Cubic inches of a #14 awg wire and a #12 wire?
#12 is 2.25 cu in.
#14 is 2.00 cu in.
What is a motor branch circuit? Define.
Would the below image showing a conductor supplying multiple motors be a branch circuit?
That portion of the circuit that extends beyond the final over current protection. No. NEC definitions
Although a wound rotor motor is used for speed control applications, what type of motor has a large speed range?
A DC motor has this. Tom Henry 2011 Journeyman Exam Questions and Answers. PP4
The normal rotation of an induction motor is? facing the front of the motor. (The front of motor is the end opposite the shaft).
Counterclockwise is the normal rotation for this type of motor, not facing the shaft; whereas it is clockwise facing the shaft. Tom Henry 2011 Journeyman Exam Questions and Answers. PP19
It's based on the direction of the rotating magnetic field, which is dependant on the phase rotation. Hence if you swap in two line leads on a three phase motor, the direction of the magnetic field and thus motor will reverse. (This would usually be T1 and T3)
What electrical apparatus concerns a Class A device?
Ground-Fault Circuit Interrupter (GfCl)- A device intended for the protection of personnel that functions to de-energize a circuit or portion thereof within an established period of time when a current to ground exceeds the values established for a class A device. NEC Definitions article 100.
open circuit test on a transformer is a test for measuring what? Define this.
iron losses are tested with this test on a transformer keeping the HV side open and using the LV side. iron loss:the loss of available energy by hysteresis and eddy currents in an electromagnetic apparatus (as a transformer) versus copper loss. Tom Henry 2011 Journeyman Exam Questions and Answers. PP30
Usually high voltage (HV) winding is kept open and the low voltage (LV) winding is connected to its normal supply. A wattmeter (W), ammeter (A) and voltmeter (V) are connected to the LV winding as shown in the figure. Now, applied voltage is slowly increased from zero to normal rated value of the LV side with the help of a variac. When the applied voltage reaches to the rated value of the LV winding, readings from all the three instruments are taken.
hot resistance of an incandescent lamp is approximately______times its cold resistance.
This type of resistance in an incandescent lamp is ten times the cold resistance. Tom Henry 2011 Journeyman Exam Questions and Answers. PP34
What is the below image a picture of?
Amphenol Plugs. They must have the wires soldered on one end
When are you allowed to support an enclosure that does not contain a device(s), other than splicing devices, or supports a luminaire(s), a lampholder, or other equipment and is supported by entering raceways only…..?
….shall not exceed 1650 cm3 or 100 in 3 in size. It shall have threaded entries or identified hubs. It shall 1 be supported by two or more conduits threaded wrench tight into the enclosure hubs. Each conduit shall be secured within 900 ram (3 ft) the enclosure, or within 450 mm (18 in.) of the enclosure if all conduit entries are on the same side.
Source: 314.23E 2017 NEC
Non-combustible surfaces that are broken or incomplete around boxes employing a flush-type cover or faceplate shall be repaired so there will be no gaps or open spaces greater than?
3 mm (1/8 in.) at the edge of the box.
Source: 314.21 NEC 2017
Is it allowable to have conductors of each phase, ground, or EGC to be grouped together in parallel conduits by isolated phase? A phase in one, B in another, and so on? Site the code section if it is allowed.
NEC 300.3B1
Exception: Conductors installed in nonmetallic raceways and run underground shall be permitted to be arranged as isolated phase, neutral, and grounded conductor installations. The race shall be installed in close proximity, and the isolated phase, neutral, and grounded conductors) shall comply with the provisions of 300.20(B)
What is another term for an ATS that is an open transition transfer switch?
open transition transfer switch is also called a break-before-make transfer switch. A break-before-make transfer switch breaks contact with one source of power before it makes contact with another. It prevents back feeding from an emergency generator back into the utility line, for example
What is another name for a closed automatic transfer switch?
A closed transition transfer switch (CTTS) is also called a make-before-break transfer switch.
A typical emergency system uses open transition, so there is an inherent momentary interruption of power to the load when it is transferred from one available source to another (keeping in mind that the transfer may be occurring for reasons other than a total loss of power). In most cases this outage is inconsequential, particularly if it is less than 1/6 of a second. these require a less than 100 millisecond transfer.
Why is single point grounding so necessary? Consider lightning.
The reference paragraph below explains that between any two points on a conductor, or lets say ground system, you may have significant potential differences as current resulting from lighting activity is introduced into this conductor or the conductors of the system. With DC current we merely consider the true circuit resistance. With AC and RF we must consider the impedance of the circuit and that is where the 600 kV of the example below comes into play.
By having all equipment, including antenna transmission lines, power, telephone, cable TV, etc, all entering the facility at nearly the same point and all being bonded to a single common ground point, little current will flow between these systems and therefore there will be essentially no difference of potential between the components of the system (everything within the shelter) during lightning activity.
Where can a system bonding jumper be landed and cite the code section.
As noted in 250.30(A) of the NEC, a system bonding jumper must be installed at the same location where the grounding electrode conductor terminates to the neutral terminal of the separately derived system; either at the separately derived system or the system disconnecting means, but not at both locations [250.30(A)(1)].
Define a system bonding jumper, And in what code cycle was this new?
The term System Bonding Jumper has been added to Article 100 in the 2011 NEC and is defined as follows: The connection between the grounded circuit conductor and the supply-side bonding jumper, or the equipment grounding conductor, or both, at a separately derived system.
What is the difference between a micrologic trip relay and and a digitrip?
Micrologic is a Schneider or Square D brand and Digitrip is an Eaton brand. The Longtime delay is set differently. Micrologic is .9 is .9 on the dial. Where Digitrip may be .9 of long time trip, and not just a .9 setting on the dial.
What is BIL and what does it mean?
Basic Insulation Level: The BIL of a transformer is a method used to specify the magnitude of the voltage surge that a transformer can tolerate without any damage to the windings and live parts of the transformer.
EPMS stands for?
Electrical Power Monitoring System, or Emergency Power Management System.
BMS stands for what?
Building Management System.
Is primary or secondary current injection preferred in breaker testing? And what is the primary difference between the two.
Primary injection is preferred because it involves passing high current through the circuit breaker, replicating actual in service current levels at a low voltage. Secondary injection involves passing a very low current (less than 50A max) into the trip unit, bypassing the CT's - this requires a special injection tester.
If you are asked “what’s the apparent power in VA of two 40W lamps with a power factor of 89%.....what is the formula?
If you know how many watts and the PF you can find the apparent power. The formula is Watts/PF=VA
Another way of looking at this is True power / (true power / apparent) = volt amps or apparent power. the true power cancels itself out.
PP 81 “Electrical Exam Preperation” Mike Holt 2014
What is another name for a closed automatic transfer switch?
A closed transition transfer switch (CTTS) is also called a make-before-break transfer switch.
A typical emergency system uses open transition, so there is an inherent momentary interruption of power to the load when it is transferred from one available source to another (keeping in mind that the transfer may be occurring for reasons other than a total loss of power). In most cases this outage is inconsequential, particularly if it is less than 1/6 of a second. these require a less than 100 millisecond transfer.
(Sp) Single pole, indicates?
ST (Single Throw) indicates?(Single pole) indicates one circuit conductor can be opened or closed. Single throw indicates possible positions of the switch other than OFF. PP 30 Motor Controls
What is a monopole array?
An array that has one positive terminal and one negative terminal. PP 155 (Photovotaic notecard set)
Contacts are divided into what categories?
Note: Normally open power poles (these are not contacts)
normally open and normally closed auxiliary contacts.
are the categories of contacts. -NJATC, Motor Controls: contractors and starters, 2010, PP 90
What is an auxiliary contact?
It is a pilot device or a secondary low voltage switching signal.
What is a shunt?
provide (an electrical current) with a conductor joining two points of a circuit, through which the current may be diverted. -dictionary.
What is it called when the DC excitation is applied to the rotor, creating an electromagnetic field with North and South poles locked with the revolving field of the stater?
This is called locked in step, in a synchronous motor. -ATP & JATC, Motors 2nd edition, 2010: Chapter 7 Synchronous motors, PP 135
If a noise (magnetic field coupling) level is not really known it is a good idea to install what ahead of each multiplier input?
A low pass filter.
-Keith H. Sueker, Power Electronics Design, 2005 PP 61 (NC set: transients)
While air cooling is the most economical way to cool servers in racks, _______ cooling is the most efficient way to remove heat generated from processors.
Water is the most efficient form of this in data centers.
A data server’s utilization effectiveness is estimated to be a disappointing _____? At Looking Glass, the PUE was at 27% and now is at what?
20% typically but it is now 7% at Look Glass. This is considered the Power Conversion Loss.
A motor thermal device is either of the__________ or the ____________.
Bi-metal type or the melting alloy (solder pot) design. -pp. 7 Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
What is PUE?
The ratio of the amount of energy used by the building ÷ the amount of energy used by the servers. Acronym means power usage effectiveness.
the PUE at looking glass is what compared to what industry average?
1.7 currently compared to the industry average of 1.5. This means total building power/server power is about 59 of 100 total.
What is the Open Compute project and what is it's mission?
The five members hoped to create a movement in the hardware space that would bring about the same kind of creativity and collaboration we see in open source software.
What is DHCP? What does it do?
DHCP is the network management protocol we use for provisioning servers in our production data centers. The Dynamic Host Configuration Protocol (DHCP) is a network management protocol used on UDP/IP networks whereby a DHCP server dynamically assigns an IP address and other network configuration parameters to each device on a network so they can communicate with other IP networks.
What does the term bare metal provisioning mean?
bare metal provisioning (to install the operating system)
The overload section of the starter, as the name implies, protects the motor from overloads and/or?
Phase failure. -PP6 Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
Overload devices are of three basic types, what are they?
Thermal, magnetic, and solid state. -PP6 Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
What is SCADA?
Supervisory control and data acquisition
Supervisory control is found where in a plant?
Supervisory control is what we actually see in the PLC (programming logic controller), SCADA (supervisory control and data acquisition), DCS (distributed control system) systems. Which is controlling whole plant or more than one field devices through a master system.
What is the acronym DCS? in regards to controls systems?
Distributed control system.
An isolator or disconnect is suitable for disconnection under what criteria regarding load?
No load is required for this to work.
what is the difference between a load break switch and a circuit breaker in regards to switching loads?
A load break switch and a circuit breaker can interrupt loads but the load break switch will not interrupt a fault.
A MOAB (motor operated air break or switch) can be used on very high voltages. These are usually found at the substation and after the service utility. Can these be opened under load?
Not usually done in a data center; however, They can interrupt a load by design but not a fault.
Transformers are always sized based on what rating?
What is the formula for this?
KVA (apparent power) is always the rating for these, not KW because they are an inductive load which results in apparent power. Apparent power is measured in kVA, while KW is used only for true power such as resistive loads.
Apparent power = KW/PF so…
kVA= IxE/1000 for KVA would not account for power factor and would be wrong as mentioned on page 19 of Master Electrician: 2014 Exam Questions & Study Guide. Ray Holder
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP82
power factor is ______ _________ of current and voltage in an AC circuit?
phase displacement.
-Source: Journeyman Electrician exam questions and answers, Tom Henry 2011.
The output of standard CT’s are usually, but not always, _____ max.
The most common CT secondary full-load current is 5 amps which matches the standard 5 amp full-scale current rating of switchboard indicating devices, power metering equipment, and protective relays.
5 amp maximum output for these. -Electricians Guide to AC Motor Controls- Richard Cox 1981 edition. PP11
Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
All current transformers are ________ polarity.
Polarity refers to the instantaneous direction of the primary current with respect to the secondary current and is typically determined by the way the transformer leads are brought out of the case. On subtractive polarity transformers the H1 primary lead and the X1 secondary lead will be on the same side of the transformer (the left side when facing the low-side bushings).
All of these have subtractive polarity, meaning they are polarity sensitive.
The black dot represents the secondary on these. Remember, they are polarity sensitive or subtractive in polarity so this is required.
Magnetic types of overload relays are of two basic types?
time limiting (Inverse time) and instantaneous trip. PP12 Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
Describe inverse time tripping and overcurrent protection. (OCPD-ovecurrent protective device)
Inverse time tripping is a characteristic of circuit breakers in which the breaker trips in more time with lower overcurrent, and less time with higher overcurrent. source:http://www.schneider-electric.us/en/faqs/FA115818/
What must be remembered regarding an instantaneous trip magnetic relay in regards to tripping?
instantaneous trip magnetic relay is not designed for normal overload use, as the primary use of this device is to Trip instantaneously at a preset current level. -PP13 Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
Solid state overload relays are adjustable from? You can do what to provide for lower ranges while increasing the solid state overload relay capacity?
0 to 120% of the units rated value. By using multiple turns through the sensing loop (one for ea. phase), for instance, two turns in a 10 amp relay can provide protection for a 20 amp motor. Source: PP 138 Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
two methods of arc quenching are?
arc chutes or blow out coils.
What is the difference to a fuse or switch that can interrupt a load per the schematic symbols?
A load break rating is always indicated with a horizontal line across the vertical symbol on the load side.
Normally in AC magnetic equipment, black wires are used in _______ and red wires are used for _______. bold lines denote the power circuit, and thin lines used to show the control circuit.
power circuits & control circuits.
Source: PP18 Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
Three wire control, as the name implies, will require three wires to control the motor circuit. What is the third wire for?
The third wire will allow use of momentary push-buttons, float switches, limit switches, pressure switches, etc.
Source: Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
throws indicate what?
Possible positions of the switch other than off indicates this. Source: PP 30 Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
SPDT is sometimes called a _________, because it can direct or transfer power to either of two loads. It will not, however, operate both loads at the same time
Single Pole Double Throw (SPDT) is sometimes called a transfer switch.
Source: (Fig- 3.7). PP33. Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls transfer switch
Reversing a 3 phase motor can be accomplished using what other than swapping two of the leads?
This can be accomplished by using a double pole double throw switch (4 way)... to reverse this motor.
How does a diesel generator produce energy?
This is a trick question.
This does not produce energy, but rather converts it to another type.
The working principle of a diesel generator is based on the law of Energy conversion i.e. “Energy can neither be created nor be destroyed but be only converted from one form to another form. Diesel generators convert some of the chemical energy, contained by the diesel fuel, to mechanical energy through combustion. This mechanical energy then rotates a crank to produce electricity. Electric charges are induced in the wire by moving it through a magnetic field
What is the current drawn when PF is .91? This question requires what mathematical formula?
watts
(pf x voltage)
What formula is used to find ‘R’ (resistance) in a length of wire for a single and 3 phase system? You will need to know the specific resistance for copper and aluminum. What are they?
R=(K×L)/(CM) single phase.
;where CM is circular mils, K is specific resistance of 12.9 for copper and 21.2 for Aluminum, and L is length. Notice the 2kli/cm would be a voltage drop calculation for single phase; where this is resistance and not VD.
the formula for VA when power factor and watts is known is what?
Watts/PF=VA
POWER QUALITY METERS (PQM) Current inputs for each channel shall be from standard instrument current transformers. And the meter burden is what? What formula is used to find the meter burden?
think of ohm's law formulas. Where Z is the resistance and I2 is half of the watt loss formula.
less than 10 milliohms.
VA=I2 xZ ;where,
Z = Total CT secondary impedance
I = Secondary current
(Generally 1 or 5 amps)
In a control CT with loops of wire through it, The relationship of the ratio of primary and secondary turns is expressed in the following
formula:
turns on the secondary/ primary turns. X1/H1
Output watts uses what formula? PP. 101 Mike Holts 2014 “Exam Preparation”. There are two formulas.
watts= HP/746; whereas, output watts accounts for losses.. INPUT WATTS/EFFICIENCY is correct.
OUTPUT IS NOT THE INPUT WATTS.
If you wanted to know the Apparent Power and you know the wattage and the power factor, how would this be expressed in a formula?
Mike Holts Exam Preparation 2014 PP 83
KW/PF=APPARENT POWER
If you know true power and power factor, can you know apparent power? And what would be the formula if you could?
APPARENT POWER=(TRUE POWER) WATTS/ PF
Mike Holts 2014 Exam Preparation PP 80
IF you have PF and Watts, can you figure out VA?
think of the power formula triangle
Yes... by using the formula
WATTS/PF=VA
Mike Holts 2014 exam preparation pp 81
formulas used to determine the power factor are?
true power over apparent power
formulas used to determine the power factor are Power factor = watts/VA.... also R/Z and various other formulas are correct.
PP 19 2017 Journeyman Electrician Exam Questions and Study Guide, Brown Technical Books: Ray Holder.
One way to find I when all you know is KVA and E in a 3 phase circuit is?
P/E(1.732)=I is another way of viewing this formula
I = VA/(volts x 1.732) PP 21 2017 Journeyman Electrician Exam Questions and Study Guide, Brown Technical Books: Ray Holder.
The true power (watts) of a single-phase circuit or load that contains inductance or capacitance can be calculated by the use of the following formula:
TP= (KVA x PF)
PP 23 2017 Journeyman Electrician Exam Questions and Study Guide, Brown Technical Books: Ray Holder.
Much like the formula to find over current protection for a load, (load/ correction factor), the formula for Number of Circuits is what?when you know VA?
LOAD VA / CIRCUIT VA= # of CIRCUITS.
PP 37 2017 Journeyman Electrician Exam Questions and Study Guide, Brown Technical Books: Ray Holder.
To find amps when KVA is known you use what formula? for single phase.
similar to the resistive or single phase calculation where P/E=I.
(KVAx1000)/E =I.
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP11
How do you find amps when using 3 phase and you know the KVA?
similar to P/E=I for the standard formula without taking into account reactive loads and the 3 phases.
(KVAx1000)/Ex1.73
Questions and Study Guide- Ray Holder.PP11
what is the formula for KW in a 3 phase circuit when the voltage and current is known?
this is the same formula for both KW and KVA
[KW=I(E)x1.732]/1000
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP20
What is the formula for KVA or VA when the current and voltage is known for 3 phase electrical systems?
KVA=[IxEx1.732]/1000. Also I/Ex1.732 would suffice as this is simply VA and not KVA. Note: this is the same for KVA and KW.
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP20
What is the formula for P when E and I are known? In a reactive 3 phase system.
the use of 1.732 is consistent in all 3 phase formulas with the use of E. If this were resistive only then we use E....and in a reactive circuit you use VA instead of E.
P=VAx1.732. for 3 phase.
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP20.
The true power (watts) of a single phase circuit or load that contains inductance or capacitance can be calculated by the use of the following formula.
remember that in a 3 phase system we use 1.732 next to E.
W=ExIxPF
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP23
the formula for the number of circuits is what? When you know the VA of the circuit and the load.
this is not the same as it is for commercial office buildings; such as, stores, banks, restaurants, etc.
LOAD VA/CIRCUIT VA= Number of circuits.
For commercial buildings we at 125% to the VA in this formula.
The formula for determining the number of general lighting branch circuits in an office building is what?
[Load VA x 125%]/circuit VA=The number of circuits in this type of building.
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP43
What is the formula used for a commercial building for the total number of circuits required, when the number of receptacles are known?
number of circuits=[180VA x number of receps]/circuit VA.
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP46.
the formula for calculating the required branch-circuits for fixed multi-outlet assemblies where the cord-connected appliances are unlikely to be used simultaneously, you can use what formula?
number of circuits=[(linear ft./5)x180VA]/circuit VA. where outlets are unlikely to be used at the same time.
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP46
To calculate the branch circuits required for fixed multi-outlet assemblies where the cord connected appliances are likely to be used simultaneously, what formula may be used?
think banks and office buildings.
number of circuits= [linear ft. x 180VA]\circuit VA. this formula is used for simultaneous loads in a commercial buildings such as a bank or office building.
Knowing how to find the number of branch circuits for lighting, how do you propose the formula would look to find the number of branch circuits for resistive heating?
Load VA x 125%/ circuit VA ... similar to lighting formula that uses the same calculation in office buildings where the lights are on for more than 3 hours at a time.
More than 3 current carrying conductors in the raceway or cable.... in an elevated ambient temperature and a raceway OR CABLE longer than 24 inches uses what formula?
required ampacity = load/temp.correction x adj. factor
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP88
What is the formula for VD in a 3 phase circuit? single phase?
Remember: the 1.732 or 2 represents the length of the circuit.
The only difference between a single and 3 phase VD calculation formula is the use of 2 versus 1.732 for a 3 phase circuit. for the use of 1.732KLI/CM.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP124
A useful formula that may be used to size conductors in a 3 phase circuit to prevent excessive voltage drop is?
CM=[1.732xKxIxD]/VD
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP126
The following formula can be used to determine the approximate distance circuit conductors may be installed to prevent excessive voltage drop in a SINGLE PHASE CIRCUIT
D=[CMxVD]/2xKxI
Where D is distance.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP127
The formula to determine the MAXIMUM LOAD when limiting VD on a single phase circuit is?
I=[CMxVD]/2xKxD
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP127
The formula to determine the MAXIMUM LOAD when limiting VD on a three phase circuit is?
I=[CMxVD]/1.732xKxD
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP128
The ohms law method for determining the voltage drop of the conductor works for what type of circuit?
this formula only works for single phase circuits ONLY.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP129
Calculate the total resistance (Rt) of the circuit: What is the formula for a series circuit?
What is theRt=R1+R2+R3+R4 Is the additive formula for a series DC circuit.
There are three basic formula methods of calculating the total resistance of parallel circuit. What are they?
The Equal Resistance method, the Product-Over-Sum , and the Reciprocal method… are the 3 ways to solve for this in a parallel circuit, versus a series circuit where it is the only additive.
The neutral of a 3-wire circuit from a 4-wire wye (system carries about the same current as?
The phase conductors.
A balanced 3-wire (480v with 120 phase angle wye), single-phase or 4-wire, three-phase multi-wire branch circuit has unbalanced current flowing only in?
A balanced 3-wire, single-phase or 4-wire, three-phase multi-wire branch circuit has unbalanced current flowing only in the ungrounded (phase) circuit conductors.
The first law of thermodynamics is a version of the law of conservation of energy, adapted for thermodynamic systems. The law of conservation of energy states what?
The law of conservation of energy states that the total energy of an isolated system is constant; energy can be transformed from one form to another, but can be neither created nor destroyed.
The second law of thermodynamics indicates the irreversibility of natural processes, and, in many cases, the tendency of natural processes to lead towards spatial homogeneity of matter and energy, and especially of temperature. This is called?
Entropy.
The third law of thermodynamics is sometimes stated as follows:
The entropy of a perfect crystal of any pure substance approaches zero as the temperature approaches absolute zero.
Entropy is defined as what?
a thermodynamic quantity representing the unavailability of a system's thermal energy for conversion into mechanical work, often interpreted as the degree of disorder or randomness in the system. this is also defined as lack of order or predictability; gradual decline into disorder.
Gustav Kirchhoff’s Current Law is one of the fundamental laws used for circuit analysis. His current law states what?
that for a parallel path the total current entering a circuits junction is exactly equal to the total current leaving the same junction, is stated in this law.
KVL or Kirchhoff’s voltage law or Kirchhoffs second law states what?
this law states the algebraic sum of the voltage in a closed circuit is equal to zero or the algebraic sum of the voltage at node is equal to zero.
the formula for applying correction factor regarding ambient temperature to Table 310.15B16 to achieve the required minimum ampacity is what?
LOAD/CORRECTION FACTOR
Or 20 amps = 16 amps (125% OCPD)
Tom Henry’s Calculations PP 39, 2011
Capacitors charge and discharge at an exponential rate when connected with what? AC Theory, NJATC 2009 PP 106
Proven by the Time Constant formula for capacitors which is what?
When connected in series with resistors
T=RxC
Versus T=L/R
Is there Capacitive reactance in a D.C. circuit and what does it oppose? AC Theory, NJATC 2009 PP 110
What is the formula for capacitive reactance?
What does this formula show?
NO, capacitive reactance only exists in an AC circuit and it opposes a change in voltage.
XC= 1/ (2pieFC)
That as the frequency increases XC decreases, or that they are inversely proportional to each other.
What is the formula for Capacitance? AC Theory, NJATC 2009 PP 113
C=1/(2pieFXc)
The formula for determining how much CEMF is produced is what? Remember: The voltage created by an inductive load is not proportional to the amount of current flow, but rather to the rate at which current is changing. AC Theory, NJATC 2009 PP 54
CEMF = (-L x Δ I)÷ Δ T
where L is inductance, I is current, and T is time
The greater the inductance, or the faster the rate of change of current, the greater the CEMF
When the magnetic field starts to collapse back into the inductor it aids the current provided by the source. Meaning what?
The formula for inductive reactance is what?
That the current lags 90 degrees behind the source. (inductive: Voltage leads Current / ELI) current lags voltage
xl=2pieFL
xl in ohms and L is inductance in henrys.
Transformer Principles and Applications PP15
The total opposition or impedance to a circuit is calculated using what formula?
Z= square root of (R2+xl2) AC Theory PP 61 Transformer Principles and Applications PP 15
The total amount of mutual induction M is calculated by the formula? AC Theory, NJATC 2009 PP 68
M=K x √(L1xl2)
Where M=mutual induction in henrys
K=decimal equivalent of coefficient of coupling
The COEFFICIENT OF COUPLING of a transformer is dependent on the portion of the total flux lines that cuts both primary and secondary windings.
The total amount of mutual induction M is calculated by the formula? AC Theory, NJATC 2009 PP 68
M=K x √(L1xL2)
Where M=mutual induction in henrys
K=decimal equivalent of coefficient of coupling
The COEFFICIENT OF COUPLING of a transformer is dependent on the portion of the total flux lines that cuts both primary and secondary windings.
What is referred to as the Q of a coil? AC Theory, NJATC 2009 PP 70. Represented by what formula?
The quality factor
Q=XL/R
The amount of time required for the current flow to reach the maximum value is expressed in time constants. In a circuit with inductance and reactance, the time constant is defined from the following formula. AC Theory, NJATC 2009 PP
T=L/R
Where T= time constant in seconds
L= Circuit inductance in henrys
R= Circuit resistance in ohms
The general formula for Voltage Drop in a single phase system is? And in a 3 phase system? And lastly in a DC system?
single phase VD=2KLI/CM
Three phase VD=1.73KLI/CM
DC system VD=I(R)
The number of poles, combined with the ac line frequency (Hertz, Hz), are all that determine the no-load revolutions per minute (rpm) of the motor. So, all four-pole motors will run at the same speed under no-load conditions, all six-pole motors will run at the same speed, and so on.The mathematical formula to remember in helping make this calculation is?
The formula is n = 60 x f /p where n = synchronous speed; f = supply frequency & p = pairs of poles per phase. The actual running speed is the synchronous speed minus the slip speed. The mathematical formula to remember in helping make this calculation is...
the number of cycles (Hz) times 60 (for seconds in a minute) times two (for the positive and negative pulses in the cycle) divided by the number of poles.
Therefore, for a 60-Hz system, the formula would be:
60 x 60 x 2 = 7,200 no-load rpm /number of poles.
For a 50-Hz system, the formula would be:
50 x 60 x 2 = 6,000 no-load rpm / number of poles.
AC generator (actually an alternator) speed is calculated using what formula? NJATC ATP, Motors 2nd edition, AC alternators, PP 60
S= (120 x F)/ poles is wrong... this formula should assume HZ x 60 seconds x 2/ number of poles. A very old description of alternating current systems sometimes give the frequency in terms of alternations per minute, counting each half-cycle as one alternation; so 12,000 alternations per minute corresponds to 100 Hz.
What is synchronous speed. As determined by the formula S=(60 seconds x HZ x 2)/poles. where HZ is hertz or cycles AC per minute and S is Synchronous speed.
In a motor, this speed is the speed at which the magnetic field rotates. If an electromagnet is present in this rotating magnetic field, the electromagnet is magnetically locked with this rotating magnetic field and rotates with the same speed of rotating field
What is the formula for Power Factor when voltage, current, and horse power is known?
Source: ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 96 The Horse Power version
What does a surge arrester do?
This is a device to protect electrical equipment from over-voltage transients caused by external (lightning) or internal (switching) events.
What is a gapless surge arrester and what does it do?
Gapless Zinc Oxide Lightening / Surge Arrester. ... Gapless zinc oxide (ZnO) surge arresters are widely used. The surge arresters are usually connected between the phase and ground terminals. They limit the voltage level in equipment such as transformers below the withstand voltage level
What is the difference between a surge arrester and surge suppressor?
The simple answer is that a surge arrester directs the above voltage surge to ground while a surge suppressor soaks the energy up and re-emits it as heat. ... A fraction of the energy will still go down the power line and secondary things like surge suppressor should be able to soak up the rest of the energy.
When the magnetic field starts to collapse back into the inductor it aids the current provided by the source. Meaning what?
The formula for inductive reactance is what?
That the current lags 90 degrees behind the source. (inductive: Voltage leads Current / ELI) current lags voltage
XL=2pieFL
XL in ohms and L is inductance in henrys.
Transformer Principles and Applications PP15
The total opposition or impedance to a circuit is calculated using what formula?
Z= square root of (R2+XL2) AC Theory PP 61 Transformer Principles and Applications PP 15
Describe the difference between an asynchronous motor and a synchronous motor.
Synchronous motor is a machine whose rotor speed and the speed of the stator magnetic field is equal.
Asynchronous motor is a machine whose rotor rotates at the speed less than the synchronous speed. ... AC Induction Motor is known as the Asynchronous Motor.
does an asynchronous motor have slip?
yes. this type of motor does have slip as opposed to an asynchronous motor.
What does a synchronous motor not have?
this type of motor does not have slip.
what is also called a doubly excited machine?
Synchronous motors are this type of machine, i.e., two electrical inputs are provided to it.
1.) Its stator winding which consists of a Wye provide three-phase supply to three-phase stator winding, and...
2.) DC to the rotor winding.
What is the phase voltage formula for a star?
VP=VL/(1.73). consider 480/1.73=277V. phases voltage is with the neutral and line voltage is across the load.
1.73 is √3
What is the line voltage of a star?
VL=1.73xVp
What is the phase voltage for a delta?
VP=VL
What is the line voltage for a delta?
Vp=VL
The utility power is lost at the MSG1 or 2 (main switchgear house MV), what provides power to the main switchboard?
The generator provides power to the main switchboard.
What provides power to the SB (switchboards 480V)?
The MSB's 480V.
where is the power meter (not PQM) located in the data center?
At the switchboard.
The 480V switchboard contains a link to isolate the A side or the B side from eachother. What is this called?
CB-2A or CB-2B
What CB is the reserve loop for the MSBs?
CB3.
Which MSB feeds the HMD line up?
MSB-04A and MSB 04B as well as MSB-1R. For all mechanical pumps and motors in the pump rooms.
What ties into the LBSB and the MGPCC?
MGPCC (mobile generator power control center) and LBSB (load bank switchboard)
CB3 reserve loop at MSB-07 and the STC's.
The core, denoted with an N.... has 480V UPSs that can equalize the load for how long?
5 minutes.
the core main output breaker or MOB is what? regarding feed.
This is what gets the UPS-N power from the core. While the UPS-Ns are fed by the MSB-N
the MOB and LBB, as well as the MBP in the core (N) are combined unless what happens?
The MIS is opened. This is like a link.
What feeds the core PDU's?
The core PDU's are fed by a core STC that is backed up by UPS's with a 5 minute EOL (equalization of load)
All of the panels in a Looking Glass data center (480V and lower power distribution panels) are provided with what upstream?
the core STC backed up by a UPS.... but all of this feeds the ATS directly upstream from the panels and associated transformers. The ATS is linked one to the next ATS via the MBP at the STC.
An RPP (reactor power panel) is how many volts at Looking Glass? And what feeds each RPP?
480V. Each RPP is fed by the reserve loop and a normal SB power supply at 480V via an air core induction isolation transformer.
Each SB and MSB has what type of power supply to PS-1 and PS-2?
A redundant UPS backup power supply at 120V from the CP in the electric room.
How many RPPs are fed from the SB? At looking Glass?
8 total for each.
the result of Tan Delta VLF (very low frequency) testing on MV cables constitutes what two values? In fact... it is a ratio of these two values.
Consider if this is resistance, current, or voltage before answering the question. The voltage uses the inherent resistance of the cable to get what result?
The tan delta is defined as the ratio between the resistive current and the capacitive current.
What is the advantage of a Delta transformer?
The delta winding allows third-harmonic currents to circulate within the transformer, and prevents third-harmonic currents from flowing in the supply line
considering a Delta with 3 phases and 3 wires... what are the available voltages?
480 Line A, B, and C. Remember that a delta can loose one phase and still provide full voltage to the load. 240 and 120V is only available in a wild leg or high leg center tap configuration.
The non-time delay fuse will hold ________ times its rated current for about _______, Dual element (time delay fuses) will hold ______their rating for _______.
5 times for 1/4th of a second
5 times for 10 seconds.
Tom Henry’s Code Calcs, PP 70
What is a dry contact?
Dry contact can refer to a secondary set of contacts of a relay circuit which does not make or break the primary current being controlled by the relay.
Can a MOAB interrupt a fault?
No.
What kind of transfer switch would be used with a generator? And what about time used for transfer?
A break before make would have to be used to avoid backfeeding a generator. Also.... industry standards are 48 seconds timed to transfer the load. This gives the generator time to come up to speed at 1800RPM... and always at 1800RPM for 60HZ.
At looking Glass, how many generators are dedicated to each MSB? (main switchboard)
one each.
What type of breaker is connected to the reserve and primary power at the MSB at looking glass?
A swing bus breaker. Slack bus also known as swing bus this bus is taken as a reference bus. generally, in the power system, there are mainly two types of buses load bus and generator bus, for these buses real power P injection specified. which is taken positive for generator bus and negative for load bus, the losses remain unknown till complete load flow solution.
For this reason, one generator bus is made to take the additional real and reactive power to supply losses in the transmission line, this type of bus is called a slack bus.
When does ground fault trip with zone selective interlocking interlock? to where?
this interlock for this is at the main breaker in the same switch gear.
surge protection is phase to phase or phase to ground?
this type of protection is both phase to phase and phase to ground.
What performs the function of equipment monitoring?
BMS modbus interface.
What parameters are monitored for equipment monitoring interface?
⇛load amps and power
⇛circuit breaker position
⇛power quality meter data
⇛SPD alarm
⇛AT auto transfer module data.
What is monitored for batteries and validation?
battery jar, string voltage, temperature, individual resistance, inter tier resistances.
overhead busways at looking glass are what type? what is the rack power distribution?
480/277VAC 4 wire and 20A server power with rack power distribution at the same with an added 48VDC.
Indoor bus duct, or underfloor cable tray is connected to each MSB from the reserve bus and the _____.
The LBSB is connected via cable tray to each reserve breaker at each MSB.
The cable tray on the reserve loop for each MSB provides what function?
This allows backfeed to each MSB OR load bank testing of any one generator.
The reserve bus (cable tray under skid) uses what type of breakers?
interlocked breakers (kirk keys) are provided for this at each MSB.
Regarding an RPP (reactor power panel) at looking glass, the in line reactor is how many watts and performs what function?
This eliminates the THD total harmonic distortion. This is usually 360W.
What function do the cam lock power panels provide?
This provides the power bypass to 480V systems for maintenance.
Cold aisle temperatures are controlled at what?
65 to 85F. Consider the hot aisle well exceeds a comfort level.
What is the relative humidity in the data center?
65%.
What provides the humidity in looking glass data centers when needed?
The Direct Evaporitive Humidifier (DEH) built into either side of the bypass (at a 45 degree offset) on the other side of the mixing / intake room provides this. As well as CRAC units with humidifiers added to them.
A built up system is what?
A penthouse second level design.
the drains for direct evaporation/ humidification require what in an built up system design?
For a data center, these require double containment and leak detection in a built up system design.
At a built up system design data center using plenums for air, they supply air to what location?
The cold aisles get the supplied air. This means they are positive pressure.
What prevents water carry over? For mechanical cooling system.
Mist eliminators.
What exhausts the hot aisle air from a penthouse style data center for looking glass?
The air from the hot aisles is exhausted by relief fans or mixed at the filter room.
Cold aisle air enters from what side of the server cabinets?
The front side of the servers receives this.
The fan array at looking glass is fed by how many bus?
The fan array is fed by 3 electrical busses at N+1 redundancy.
What is the purpose of the VFD’s for the penthouse?
They modulate the fan speed and load while minimizing costs.
What type of system is used for all mechanical control, data logging, monitoring, and alarm functions?
A DDC (direct digital control) system does this for the entire mechanical system. Newer designs use PLC’s.
Does the BMS system monitor server power use?
No. The BMS system does not monitor this in the data hall.
What is interfaced with the fuel system, VESDA, fire alarms, and critical point alarms?
The BMS system (building management system) monitors this.
There are how many feeds to the numeric MSG.
two breakers each from A and B utility source. Each substation transformer can feed a building and a half.
The numeric MSG’s use what type of bus?
main tie tie main.
N+1 means what? would a generator count as plus 1?
This means normal power plus 1. Versus 2N which is 2 normal power sources or double normal power. The generator would be the same available power (wattage) and therefor just N.
The MSB failures tolerated are what? At looking Glass.
just one per half of the building. A and B and C and D reserve boards separate.
individual conductors shall be insulated or covered. What is the exception? Considering a grounded conductor.
The grounded conductor of a multi conductor cable shall be permitted to be bare. NEC 230.22 exc.
the difference between a neutral and a grounded circuit conductor is?
A. only a neutral will have equal potential to the ungrounded conductors
B. only a neutral outer covering his white or natural gray
C. only a neutral carries unbalanced current
D. there is no difference
A. only a neutral will have equal potential to the ungrounded conductors
B. only a neutral outer covering his white or natural gray
C. only a neutral carries unbalanced current
D. there is no difference
in the NEC handbook under Article 200. 1 it states "the grounded conductor is often, but not always, the neutral conductor. As defined in Article 100, a neutral conductor is one that is connected to the neutral point of an electrical system. In a single phase, 2 wire or 3 phase, corner grounded Delta system, the intentionally grounded conductor is not a neutral conductor, because it is not connected to a system nuetral point.
power factor is ______ _________ of current and voltage in an AC circuit?
phase displacement. Source: Journeyman Electrician exam questions and answers, Tom Henry 2011. Also it is the formula/ratio of TP/AP (true power to apparent power and R/Z (Resistance to impedance. The angle theta in a voltage or impedance triangle as well.
hysteresis is?
A. the tool used to read the specific gravity of a battery
B the lagging of magnetism, in a magnetic metal, behind the magnetizing flux which produces it.
C. The opposite of impedance
D. none of these
A. the tool used to read the specific gravity of a battery
B the lagging of magnetism, in a magnetic metal, behind the magnetizing flux which produces it.
C. The opposite of impedance
D. none of these
PVC shall have a minimum burial depth of?
18 inches. source: table NEC 300.5, for 1KV to 22KV, above which the burial depth increases 6 inches.
is enamel painted conduit allowed to be used outdoors?
No.
Source: n.e.c 306.1
the Wheatstone bridge method is used for accurate measurements of?
Resistance
A Wheatstone bridge is an electrical circuit used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component. Its operation is similar to the original potentiometer. It was invented bySamuel Hunter Christie in 1833 and improved and popularized by Sir Charles Wheatstone in 1843. One of the Wheatstone bridge's initial uses was for the purpose of soils analysis and comparison.
which of the following is true?
A. EMT may be threaded
B. the white colored conductor connected to the silver colored post on a duplex receptacle on a 120 volt two wire branch circuit is called the neutral conductor
C. plastic water pipe is approved to be used for electrical conduit D. the screw shell of a lampholder may support a fixture Weighing 6 pounds.
D. Per NEC 314.27A1 exc. a vertically mounted luminaire or lampholder weighing not more than 6 pounds shall be permitted to be supported on other boxes or plaster rings that are secure to other boxes, provided that the lumineer or its supporting yoke, or the lamp holder, is secured to the box with no less than two number 6 or larger screws.
when a circuit breaker is in the open position do you have a short in the grounded or the ungrounded conductor?
either. However, if the question poses an ungrounded Delta system then it would not include the neutral and this is how Europe does things. The Wye system is rarely common. Remember also a neutral carries unbalanced load and a grounded conductor does not. Tom Henry’s 2011 Journeyman Electrician exam questions and answers pp 21
wire connectors are generally classified as what type? Thermal or pressure?
both.
voltage of a circuit is best defined as?
the effective difference of potential between two conductors. Also represented by .707(Peak voltage)
When calculating a single motor’s wire size you find the FLC (full load current) wire size in the ampacity tables 310.15(B)2(6) in 2015, is this the wire size?
At what voltage does part 2 of art 430 apply?
No. An adjustment factor of 125 percent must be applied for a continuous DUTY motor. NEC 430.22 or art 430 part 2.
part 2 (motor circuit conductors) of art 430 shall not apply to motor circuits over 1000 NOMINAL volts. (Nor does part 3: Motor and branch circuit overload protection)
please note that in the 2017 handbook it states in the informational section part 3 art. 430(A)1 that a continuous duty motor is not the same as a continuous load. As defined in art 100 by the termduty.
what is the difference between the terms continuous duty and continuous load in NEC art 100 definitions?
Continuous duty and continuous load are not the same. Duty refers to operation at a substantially constant load for an indefinitely long time. Whereas, load is for maximum current for 3 hours or more.
What is the current drawn when PF is .91? This question requires what mathematical formula?
watts
pf x voltage
What must be remembered when using the lighting load demand factors, table 220.42 when calculating the total number of branch circuits for illumination?
That table 220.42 “lighting load demand factors” shall not be used in determining the number of branch circuits.
The amperage in a dual voltage motor will be ______ if the voltage is doubled despite ohm’s law finding I using R.
Example question: A dual-voltage three-phase motor draws a current of 45 amperes when connected to a 240 volt, three phase circuit. How much current will the same motor draw if connected to a 480 volt three-phase circuit? Source: Electrician’s exam preparation guide, Dale C. Brickner, 2011: PP 48
halfed. Remember that a dual voltage motor will have the winding in series for high voltage and parallel for low voltage.
What formula is used to find ‘R’ (resistance) in a length of wire? You will need to know the specific resistance for copper and aluminum. What are they?
R=K×L CM ;where CM is circular mils, K is specific resistance of 12.9 for copper and 21.2 for Aluminum, and L is length. Notice the 2kli/cm would be a voltage drop calculation for single phase.
Motor branch circuits and feeders ocpd is rounded up or down?
Motor branch circuits are rounded up and feeders are rounded down.
What is the Cubic inches of a #14 awg wire and a #12 wire?
#12 is 2.25 cu in.
#14 is 2.00 cu in.
What is a motor branch circuit? Define.
Would the below image showing a conductor supplying multiple motors be a branch circuit?
That portion of the circuit that extends beyond the final over current protection. No. NEC definitions
Noninsulated busbars will have a minimum space of_______ inches between the bottom of enclosure and busbars. What about insulated busbars?
10 inches is the maximum space between enclosures and this. NEC T408.5 And 8 inches if insulated.
Although a wound rotor motor is used for speed control applications, what type of motor has a large speed range?
A DC motor has this. Tom Henry 2011 Journeyman Exam Questions and Answers. PP4
The normal rotation of an induction motor is? facing the front of the motor. (The front of motor is the end opposite the shaft).
Counterclockwise is the normal rotation for this type of motor, not facing the shaft; whereas it is clockwise facing the shaft. Tom Henry 2011 Journeyman Exam Questions and Answers. PP19
It's based on the direction of the rotating magnetic field, which is dependant on the phase rotation. Hence if you swap in two line leads on a three phase motor, the direction of the magnetic field and thus motor will reverse. (This would usually be T1 and T3)
What electrical apparatus concerns a Class A device?
Ground-Fault Circuit Interrupter (GfCl)- A device intended for the protection of personnel that functions to de-energize a circuit or portion thereof within an established period of time when a current to ground exceeds the values established for a class A device. NEC Definitions article 100.
open circuit test on a transformer is a test for measuring what? Define this.
iron losses are tested with this test on a transformer keeping the HV side open and using the LV side. iron loss:the loss of available energy by hysteresis and eddy currents in an electromagnetic apparatus (as a transformer) versus copper loss. Tom Henry 2011 Journeyman Exam Questions and Answers. PP30
Usually high voltage (HV) winding is kept open and the low voltage (LV) winding is connected to its normal supply. A wattmeter (W), ammeter (A) and voltmeter (V) are connected to the LV winding as shown in the figure. Now, applied voltage is slowly increased from zero to normal rated value of the LV side with the help of a variac. When the applied voltage reaches to the rated value of the LV winding, readings from all the three instruments are taken.
hot resistance of an incandescent lamp is approximately______times its cold resistance.
This type of resistance in an incandescent lamp is ten times the cold resistance. Tom Henry 2011 Journeyman Exam Questions and Answers. PP34
What is the below image a picture of?
Amphenol Plugs. They must have the wires soldered on one end
When are you allowed to support an enclosure that does not contain a device(s), other than splicing devices, or supports a luminaire(s), a lampholder, or other equipment and is supported by entering raceways only…..?
….shall not exceed 1650 cm3 or 100 in 3 in size. It shall have threaded entries or identified hubs. It shall 1 be supported by two or more conduits threaded wrench tight into the enclosure hubs. Each conduit shall be secured within 900 ram (3 ft) the enclosure, or within 450 mm (18 in.) of the enclosure if all conduit entries are on the same side.
Source: 314.23E 2017 NEC
Non-combustible surfaces that are broken or incomplete around boxes employing a flush-type cover or faceplate shall be repaired so there will be no gaps or open spaces greater than?
3 mm (1/8 in.) at the edge of the box.
Source: 314.21 NEC 2017
Is it allowable to have conductors of each phase, ground, or EGC to be grouped together in parallel conduits by isolated phase? A phase in one, B in another, and so on? Site the code section if it is allowed.
NEC 300.3B1
Exception: Conductors installed in nonmetallic raceways and run underground shall be permitted to be arranged as isolated phase, neutral, and grounded conductor installations. The race shall be installed in close proximity, and the isolated phase, neutral, and grounded conductors) shall comply with the provisions of 300.20(B)
What is another term for an ATS the is an open transitions transfer switch?
open transition transfer switch is also called a break-before-make transfer switch. A break-before-make transfer switch breaks contact with one source of power before it makes contact with another. It prevents backfeeding from an emergency generator back into the utility line, for example
What is another name for a closed automatic transfer switch?
A closed transition transfer switch (CTTS) is also called a make-before-break transfer switch.
A typical emergency system uses open transition, so there is an inherent momentary interruption of power to the load when it is transferred from one available source to another (keeping in mind that the transfer may be occurring for reasons other than a total loss of power). In most cases this outage is inconsequential, particularly if it is less than 1/6 of a second. these require a less than 100 millisecond transfer.
Why is single point grounding so necessary? Consider lightning.
The reference paragraph below explains that between any two points on a conductor, or lets say ground system, you may have significant potential differences as current resulting from lighting activity is introduced into this conductor or the conductors of the system. With DC current we merely consider the true circuit resistance. With AC and RF we must consider the impedance of the circuit and that is where the 600 kV of the example below comes into play.
By having all equipment, including antenna transmission lines, power, telephone, cable TV, etc, all entering the facility at nearly the same point and all being bonded to a single common ground point, little current will flow between these systems and therefore there will be essentially no difference of potential between the components of the system (everything within the shelter) during lightning activity.
Consider RF transmission line theory. A quarter wave length or odd multiple of a quarter wavelength of transmission line at its resonate frequency will appear as what?
Consider RF transmission line theory. A quarter wave length or odd multiple of a quarter wavelength of transmission line at its resonate frequency will appear "open" at the source end even if the opposite (load) end of the transmission line is effectively "short" circuited.
Http://www.mikeholt.com/mojonewsarchive/GB-HTML/HTML/Single-Point-Ground~20040427.phpd segment of the spectrum
-mike holt
According to this section, if the grounding electrode conductor is connected to a single ground rod or multiple ground rods, the grounding electrode conductor is not required to be bigger than No._____copper or No. ___aluminum. Likewise, any connection to one or more concrete-encased electrodes, such as ½ in. rebar, does not need to be larger than No. 4 copper.
According to this section, if the grounding electrode conductor is connected to a single ground rod or multiple ground rods, the grounding electrode conductor is not required to be bigger than No. 6 copper or No. 4 aluminum. Likewise, any connection to one or more concrete-encased electrodes, such as ½ in. rebar, does not need to be larger than No. 4 copper.
The reason for these limits is that the purpose of the grounding electrode conductor is not to carry fault current. The job of the grounding electrode conductor is to connect the non-current carrying parts of the electrical system to the earth and keep the potential on enclosures and conduit to 0 volts
Is the the purpose of the GEC to conduct fault current?
source: https://www.jadelearning.com/jadecc/courses/UNIVERSAL/NEC05.php?imDif=10109.1
no. The reason for these 6awg cu to a single ground rod and 4awg encased (both max) is that the purpose of the grounding electrode conductor is not to carry fault current. The job of the grounding electrode conductor is to connect the non-current carrying parts of the electrical system to the earth and keep the potential on enclosures and conduit to 0 volts. It also serves to conduct lightning strikes.
Where can a system bonding jumper be landed and cite the code section.
As noted in 250.30(A) of the NEC, a system bonding jumper must be installed at the same location where the grounding electrode conductor terminates to the neutral terminal of the separately derived system; either at the separately derived system or the system disconnecting means, but not at both locations [250.30(A)(1)].
Define a bonding jumper, system. And in what code cycle was this new?
The term Bonding Jumper, System has been added to Article 100 in the 2011 NEC and is defined as follows: The connection between the grounded circuit conductor and the supply-side bonding jumper, or the equipment grounding conductor, or both, at a separately derived system.
What is the difference between a micrologic trip relay and and a digitrip?
Micrologic is a Schneider or Square D brand and Digitrip is an Eaton brand. The Longtime delay is set differently. Micrologic is .9 is .9 on the dial. Where Digitrip may be .9 of long time trip, and not just a .9 setting on the dial.
What is BIL and what does it mean?
Basic Insulation Level: The BIL of a transformer is a method used to specify the magnitude of the voltage surge that a transformer can tolerate without any damage to the windings and live parts of the transformer.
EPMS stands for?
Electrical Power Monitoring System.
BMS stands for what?
Building Management System.
Is primary or secondary current injection preferred in breaker testing? And what is the primary difference between the two.
Primary injection is preferred because it involves passing high current through the circuit breaker, replicating actual in service current levels at a low voltage. Secondary injection involves passing a very low current (less than 50A max) into the trip unit, bypassing the CT's - this requires a special injection tester.
If you are asked “what’s the apparent power in VA of two 40W lamps with a power factor of 89%.....what is the formula?
If you know how many watts and the PF you can find the apparent power. The formula is Watts/PF=VA
PP 81 “Electrical Exam Preperation” Mike Holt 2014
Capacitance is measured in what? AC Theory, NJATC 2009 PP 91
Farads
Capacitors have the characteristic to oppose what? AC Theory, NJATC 2009 PP 91
To oppose a change in voltage. They are used in motor variable frequency drive applications for this reason. They are said to block DC and pass AC. They are also used in AC to DC full wave bridge rectifiers to filter the DC and also on generators for this same reason on the voltage regulator.
Capacitors are used to block and pass what? voltage, current, static, etc. Which one? AC Theory, NJATC 2009 PP 91
Regarding the above statement, do the electrons pass through the insulating dielectric and/ or exert electrical pressure? AC Theory, NJATC 2009 PP 91
Block DC and pass AC. Direct current doesn’t flow through a capacitor, in an alternating-current circuit, the electrons in the circuit move back and forth to alternately charge the capacitor, first in one direction, and then in the other. A capacitor permits current to flow because of its ability to store ‘ and then discharge the energy as the alternating current flows the opposite direction. Source: Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 NEC. PP 69
The electrons do not pass through the dielectric plate but do exert electric pressure.
Using scientific notation, what is Micro, Nano, and Pico? AC Theory, NJATC 2009 PP 91
Micro 10>(-6)
Nano 10>(-9)
Pico 10>(-12)
The symbol for a fixed and variable capacitor is what? AC Theory, NJATC 2009 PP 91
The general formula for capacitance is what? AC Theory, NJATC 2009 PP 92
This formula is used to do what? AC Theory, NJATC 2009 PP 92
C = Q/V
where:
C= capacitor value in farads
Q= charge in coulombs
V= voltage applied
This formula is used to compare the charge a capacitor can hold per volt that is applied to the capacitor. The larger the plates the more the voltage.
Capacitors appear to oppose a change in ______. AC Theory, NJATC 2009 PP 93
voltage: block dc but pass ac as well.
The formula for calculating the capacitance of a capacitor measured in farads is? AC Theory, NJATC 2009 PP 92
C = .225AK/10^6D
where:
C = capacitance in microfarads
A = cross-sectional area of one plate in square inches
K = dielectric constant of the material between the plates (for air K is 1)
d = the thickness of the dielectric (or the distance between the plates) measured in inches
What is the relationship between the current and voltage in a capacitor? AC Theory, NJATC 2009 PP 97
The current in the capacitor circuit leads the voltage across the capacitor by 90 electrical degrees. (ELI the ICE man)
Capacitors designed for use in AC circuits are considered what? AC Theory, NJATC 2009 PP 98
Non-polarized, meaning no specific voltage polarity. Polarized would be indicated WVDC (working volts DC) or a +/- stamp.
What abbreviation means that a capacitor is rated for a maximum voltage in DC terms? AC Theory, NJATC 2009 PP 99
WVDC: working volts DC
Polarized capacitors are indicated how and used in what type of voltage? AC Theory, NJATC 2009 PP 99
By a positive or negative marked leads and used only in DC voltage.
The plate with a lack of electrons in a capacitor has a ______charge, where the plate with an excess of electrons has a ______ charge. AC Theory, NJATC 2009 PP 100
positive
negative
What is the relationship between the voltage rating and the thickness of the dielectric in a capacitor? AC Theory, NJATC 2009 PP 104
The voltage rating is decreased proportionally to the thickness of the dielectric.
What is a shorted capacitor and how does this happen?
Shorted: current flows = really low ohmic value….the more the capacitor is charged, the stronger the electrical field. If the capacitor is overcharged, the electrons from the negative plate could be pulled through the insulation to the positive plate- If this happens, the capacitor is said to have broken down (shorted). Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 NEC PP 70.
How do you test a capacitor? AC Theory, NJATC 2009 PP 105
What are the symptoms of a leaky / shorted capacitor?
By using an ohm-meter and watching for an ohmic spike as he capacitor charges and current flow decreases, and then as current ceases an infinite ohmic value is given.
Leaky: current flows = never reaches infinite ohms
Shorted: current flows = really low ohmic value….the more the capacitor is charged, the stronger the electrical field. If the capacitor is overcharged, the electrons from the negative plate could be pulled through the insulation to the positive plate- If this happens, the capacitor is said to have broken down (shorted). Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 NEC PP 70.
Capacitors charge and discharge at an exponential rate when connected with what? AC Theory, NJATC 2009 PP 106
Proven by the Time Constant formula for capacitors which is what?
When connected with resistors or in series with resistors
T=RxC
Versus T=L/R
Is there Capacitive reactance in a D.C. circuit and what does it oppose? AC Theory, NJATC 2009 PP 110
What is the formula for capacitive reactance?
What does this formula show?
NO, capacitive reactance only exists in an AC circuit and it opposes a change in voltage.
XC= 1/ (2pieFC)
That as the frequency increases XC decreases, or that they are inversely proportional to each other.
What is the formula for Capacitance? AC Theory, NJATC 2009 PP 113
C=1/(2pieFXc)
Inductors store energy in a _________, and capacitors store energy in a__________. AC Theory, NJATC 2009 PP 91
magnetic field
electrostatic field
It has two leads, the anode and the cathode, which is where it gets its name from. http://www.funtrivia.com
Diode. The greek words ana and hodos means up and way, so this is the negative lead. The greek words katta and hodos means down and way, and therefore is the positive lead, using conventional electron theory.
______ were used for logic circuits in some of the earliest computers. They were later replaced by modern semiconductors and are used to switch high voltage circuits. http://www.funtrivia.com
Relays. Modern semiconductors such as the PNP transistor or the NPN transistor use a base collector and emitter to switch a circuit.
This is a type of semiconductor in which the flow of current can be controlled though a base or gate terminal it is usually used for electronic switching or amplifiers. http://www.funtrivia.com
Transistor
This consists of usually two coil windings which usually share a magnetic core. It is used to convert an ac source or signal into another ac source or signal with same power (ideally) but different voltage and current. http://www.funtrivia.com
transformers
This is a special type of diode that breaks down when a critical reverse voltage is applied. it is most commonly used to regulate voltage. http://www.funtrivia.com
Zener diode
This is a special type of diode that lights up when a small voltage is applied. They are usually used as indicators or in numerical or alphanumerical displays. http://www.funtrivia.com
LED. LED's use mili-amps and therefore large amounts of power is displays and therefore LCD's using milliamps are preferred.
A multi-segment rotating connection that is connected to the armature windings defines what term? AC Theory NJATC 2nd Ed. 2009, PP 341
A Commutator is connected to this.
Impedance is a combination of what 3 components in AC theory?
resistance, inductive reactance, and capacitive reactance compose the 3 parts of this.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 NEC. PP63
Alternating current is primarily used because it can be transmitted ________ by transforming it to high-transmission level voltages then converting this voltage back to lower distribution voltage levels. High-voltage transmission lines allow for the transmission of alternating-current at high voltage, and relatively low current. High-voltage transmission, with the outcome of lower current, results reduced voltage drop in the transmission lines. Conductors and electrical equipment are sized based on the current in the lines, so the lower current levels also allow the use of smaller wiring smaller electrical equipment.
inexpensively.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 NEC. PP64
Although it is important to note that the voltage drop calculation for AC requires the use of VD=1.73KLI/CM versus 2KLI/CM for DC systems. This means that a 120volt DC system versus a 120volt AC system with the same distance and wiring will have a smaller number as the resulting voltage drop in an AC system. As illustrated by the calculations below for a 100ft long and 15 amp circuit using number 12AWG respectively.
VD=2KLI/CM or. VD=1.73KLI/CM
VD=2x12.9x100x15/6530=5.93 vd
VD=1.73x12.9x100x15/6530=5.17 vd
magnitude of the voltage produced depends upon? In AC voltage.
The number of turns of wire, the strength of the Magnetic field, and the speed at which the coil rotates determines this.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 NEC. PP 64
The rotating conductor loop is called a “_____” or “_________.” “_____” or " _______” rings and carbon brushes are used to connect the output voltage from the generator to an external circuit.
rotor or armature and slip or collector rings accomplish this loop to output voltage. Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 NEC. PP 64
Small single-phase ac generators have a conductor loop rotating inside a magnetic field.
Note: Larger ac generators have a rotating ____________
magnetic field inside stationary conductors. Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 NEC. PP 65
Using electromagnets permits the strength of magnetic field (and thus the lines of force) to be modified, thereby controlling __________.
the output voltage can be controlled using this for magnetism in a generator.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 NEC. PP 65
_____ generators are separately excited. Batteries or small dc generator are typically used with the ac generator.
All of these are separately excited.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation PP 65
Devices that intentionally introduce capacitance into circuits are called “capacitors.” An older term for these components is “_________.”
condensers is another term for this.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, Based on the 2014 NEC PP 69
Be careful when working on a circuit that capacitors; such as, those found in ________. Capacitors can store large amounts to energy a long period of time. They can present a shock hazard after the power has been removed.
Such as those found in variable speed drives. You must be careful when working around these as they can carry a charge after the circuit is off.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP70
Capacitance is inversely proportional to _________. The closer the plates of the capacitor are to each ‘ the greater the capacitance and, conversely, the greater the distance is between the plates, the lower the capacitance.
The distance between the capacitor plates is inversely proportional to this.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP 71
the voltage induced within conductor caused by its own expanding and collapsing magnetic field known as “_________”. Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP73
self-induced voltage is this in regards to the expanding and collapsing field in AC. This is also known as VAR or Volt Amps Reactive which is the energy stored in the collapsing field.
CEMF aids or opposes current flow?
This either opposes or aids conductor current flow. As alternating current increases, the polarity of the induced volt(CEMF) within the conductor opposes the conductor’s current. As it tries to prevent the current from increasing. However, as alternating current decreases, the polarity of the induced voltage (CEMF) within the conductor aids the conductor’s current and tries to prevent the current from decreasing.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP73
Connecting capacitors in parallel and series does what regarding total capacitance?
Connecting these in parallel has the effect of increasing the plate surface area, and increasing the capacitance by the sum of the capacitors. Connecting capacitors in series has the effect of increasing the dielectric and decreasing the capacitance. Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 NEC PP 71
To ground a capacitor you do what?
To ground a capacitor you need a conducting path across BOTH of the terminals of the capacitor. Not just on one terminal. Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 NEC PP 70
Does current flow through a charged capacitor?
Except for a small amount of current leakage through the dielectric material, current does not flow through a charged capacitor. Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 NEC PP 69
What is a parallel inductor / capacitor circuit called?
Parallel inductor/capacitor circuits are commonly known as tank circuits.
What is a tank circuit’s natural frequency called?
A tank circuit’s natural frequency, called the resonant frequency, is determined by the size of the inductor and the size of the capacitor, according to the following equation:
Where the magnetic field is at the zero reference line (0°. 180°, and 360°), is voltage is being induced back onto the conductor?
Where the magnetic field is at the zero reference line (0°. 180°, and 360°), no voltage is being induced back onto the conductor. Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 NEC PP 73
Where the magnetic field is at the zero reference line (?°. ?°, and ?°), no voltage is being induced back onto the conductor. What are the zero reference lines in degree form?
Where the magnetic field is at the zero reference line (0°. 180°, and 360°), no voltage is being induced back onto the conductor. Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 NEC PP 73
just remember that alternating-current flow contains additional element (reactance) that opposes the flow of electrons, besides conductor resistance. What is the difference between Voltage and current fundamentally in a circuit regarding flux and electrons? You do not need to memorize this, but just understand it.
Voltage is electrical pressure usually expressed as CEMF or as an induced voltage by the relative motion between a conductor and a magnet or the collapsing field creating the same relationship; whereas, flux is current and is taking into account the “R” relationship, which may be the 180 degree out of phase relationship with the applied voltage and the collapsing field opposing a change in current, becoming a VA number and not P.
which is easier to transform? AC or DC? NJATC, AC Theory 2nd edition, 2009, WB 9
AC
Each time an alternator completes one complete 360 degree rotation it is called what? NJATC, AC Theory 2nd edition, 2009, WB 10
A cycle
In an AC generator what changes to cause polarity changes? NJATC, AC Theory 2nd edition, 2009, WB 10
The flux field (left hand rule)
When a conductor cuts the magnetic flux lines at ___ degrees, the maximum voltage will be induced into the conductor. NJATC, AC Theory 2nd edition, 2009, WB 11
90 degrees
The time required for one cycle or two alternations is what? NJATC, AC Theory 2nd edition, 2009, WB 12
A period
What is the average AC voltage for a full cycle of a perfect sine wave? NJATC, AC Theory 2nd edition, 2009, WB 12
zero, because the average is the actual average of all peak values across a full cycle.
Current flow from a battery is generally considered from what polarity to what? NJATC, AC Theory 2nd edition, 2009, WB 34
- to +
The left hand generator rule uses the thumb, forefinger, and the next finger, representing what? NJATC, AC Theory 2nd edition, 2009, WB 34
thumb: motion
Forefinger: field
Next finger: current
A general rule of thumb for ignoring inductance or capacitance in field resistive calculations is what? NJATC, AC Theory 2nd edition, 2009, WB 37
Generally at 50-60 HZ electricians in the field will ignore inductive or capacitive elements in resistive calculations, but at higher frequencies you cannot. Also, if you answered the resistance is 1/10th or less the inductance then you are also correct.
An AC circuit is solved at 50 to 60 HZ like a DC circuit but uses what type of AC value? NJATC, AC Theory 2nd edition, 2009, WB 37
However: Effective alternating-current voltage or effective ac current is the equivalent value of direct-current voltage or dc current that will produce the same amount of heat in a resistor. Mike Holt’s Illustrated Guide to Electrical Exam Preparation, Based on the 2014 NEC PP 68
RMS or effective
Peak = 1.414(RMS/eff) a.k.a. max instantaneous value
Effective (RMS) = .707(peak)
Average = .637(peak)
Peak to peak = 2(peak)
Current and voltage in an AC purely resistive circuit are in or out of phase? NJATC, AC Theory 2nd edition, 2009, WB 37
in
The opposition to current change is called what?
This opposition to current change is called reactance, rather than resistance; which would be the opposition to current.
What two factors not present in a DC circuit affect the opposition to current flow in an AC circuit? NJATC, AC Theory 2nd edition, 2009, WB 38
Eddy currents and skin effect: remember that skin effect increases as the frequency increases. I.E. harmonics.
Concerning induced voltage and applied voltage, these two elements are how far out of phase with one another? NJATC, AC Theory 2nd edition, 2009, PP 49
Applied voltage and induced voltage (CEMF) are 180 degrees out of phase with each other
Capacitors oppose a change in?
Voltage.
Inductors oppose a change in what? NJATC, AC Theory 2nd edition, 2009, PP 50
basic rule: Inductors always oppose a change in an AC current.
How many time constants does it take for circuit current to reach its maximum value in an inductive circuit? What is this Maximum value? NJATC, AC Theory 2nd edition, 2009, WB 42
5 time constants
Maximum value is considered 99.5%
Does a coil change its henry value with a change of frequency or a change in the current value? NJATC, AC Theory 2nd edition, 2009, PP 55
NO
The Henry is the unit of measure for inductance. A coil has an inductance of 1 henry when...? NJATC, AC Theory 2nd edition, 2009, PP 52
...a current change of one ampere per second causes an induced voltage of 1 volt.
The formula for determining how much CEMF is produced is what? Remember: The voltage created by an inductive load is not proportional to the amount of current flow, but rather to the rate at which current is changing. AC Theory, NJATC 2009 PP 54
CEMF = -L xΔ I Δ T
where L is inductance, I is current, and T is time
The greater the inductance, or the faster the rate of change of current, the greater the CEMF
In a purely inductive circuit the current lags behind the applied voltage by? NJATC, AC Theory 2nd edition, 2009, PP 57
90 degrees
What is the phase relationship between CEMF to applied voltage and current to applied voltage? AC Theory, NJATC 2009 PP 58
CEMF is 180 degrees out of phase with applied voltage and the current lags the applied line voltage by 90 degrees. However:CEMF either opposes or aids conductor current flow. As alternating current increases, the polarity of the induced volt(CEMF) within the conductor opposes the conductor’s current and tries to prevent the current from increasing. But, as alternating current decreases, the polarity of the induced voltage (CEMF) within the conductor aids the conductor’s current and tries to prevent the current from decreasing. This is also known as VAR or volt amps reactive.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP74
The angle that the current lags the voltage through the coil is what? AC Theory, NJATC 2009 PP 61
The same angle the impedance vector makes in relation to the resistance vector.
When doing quick approximations for the impedance of a coil the ratio of the inductive reactance to the resistance is considered. If the resistance is less than ______ of the Xl, then we disregard the R and claim the total opposition of the coil is made up of reactance. AC Theory, NJATC 2009 PP 67
1/10th
Concerning coefficient of coupling, when voltage across the primary of a transformer does not reach the secondary in its entirety, what is this defined as? Source: http://www.tpub.com/neets/book2/5f.htm 2015
LEAKAGE INDUCTANCE is assumed to drop part of the applied voltage, leaving less voltage across the secondary.
Concerning a transformer and coefficient of coupling; since the counter emf in the primary is equal (or almost) to the applied voltage, a proportion may be set up to express the value of the voltage induced in terms of the voltage applied to the primary and the number of turns in each winding. This proportion also shows the relationship between the number of turns in each winding and the voltage across each winding. This proportion is expressed by the equation: Source: http://www.tpub.com/neets/book2/5f.htm 2015
The total amount of mutual induction M is calculated by the formula? AC Theory, NJATC 2009 PP 68
M=K x √(L1xL2)
Where M=mutual induction in henrys
K=decimal equivalent of coefficient of coupling
The COEFFICIENT OF COUPLING of a transformer is dependent on the portion of the total flux lines that cuts both primary and secondary windings.
Two coils need to be oriented to one another in what way to provide coefficient of coupling and in what way to avoid this. AC Theory, NJATC 2009 PP 68 Tech Tip
Two coils placed parallel to one another to create a mutual induction or perpendicular to avoid it.
What is referred to as the Q of a coil? AC Theory, NJATC 2009 PP 70
Represented by what formula?
The quality factor
Q=XL/R
In an impedence triangle the angle theta represents what? AC Theory, NJATC 2009 PP 71
It represents the actual angle of lag that the current lags behind the voltage in the circuit. Also known as power factor.
Normally the lagging angle of current is not measured in the residential application, but that same angle is measured and may be charged for if it is too large in what type of accounts? AC Theory, NJATC 2009 PP 72 Tech Tip
commercial accounts
In a voltage triangle, what are the following parts? AC Theory, NJATC 2009 PP 77
Hypotenuse ?
Adjacent ?
Opposite ?
When a circuit containing both resistance and inductance is connected to alternating current, the total current will lag the applied voltage at an angle between 0 and 90. The exact amount of the phase angle difference is determined by what ratio? AC Theory, NJATC 2009 PP 78
ratio of XL/R
What is defined as energy stored in a magnetic field or an electrostatic field and is returned to the circuit as the fields diminish. AC Theory, NJATC 2009 PP 80
Reactive power
power factor is the cosine of theta in which triangles? AC Theory, NJATC 2009 PP 80
impedance, voltage, and power
The movement of the magnetic field is energy and that energy is stored in the magnetic field is a statement that best describes what term? AC Theory, NJATC 2009 PP 80
Reactive power measured in volt amps
The power factor is an angular measure. True or False. AC Theory, NJATC 2009 PP 82
False, the power factor is a ratio.
T/A
R/Z
W/VA
The amount of time required for the current flow to reach the maximum value is expressed in time constants. In a circuit with inductance and reactance, the time constant is defined from the following formula. AC Theory, NJATC 2009 PP
T=L/R
Where T= time constant in seconds
L= Circuit inductance in henrys
R= Circuit resistance in ohms
Note: The first time constant is 63.2 percent of max current and takes 5 time constants for 99.2 percent of current to rise or decay.
The time constants are used for what purpose? AC Theory, NJATC 2009 PP 85
The time constants are used to protect a circuit from the voltage spike caused by a collapsing inductor magnetic field, which may ruin other circuit components.
The general formula for Voltage Drop in a single phase system is? And in a 3 phase system? And lastly in a DC system?
single phase VD=2KLI/CM
Three phase VD=1.73KLI/CM
DC system VD=I(R)
Lighting strikes are passed on to the distribution lines in two ways and are defined how? What are they? Keith H. Sueker, Power Electronics Design, 2005 PP 57 (NC set: transients)
differential modes: Voltage between the power line conductors
common modes: voltage of the several conductors to ground
Differential-mode voltages are passed directly through transformers and appear where & how? Keith H. Sueker, Power Electronics Design, 2005 PP 57 (NC set: transients)
on the secondaries as transformed by the turns ratio.
Explain the construction of an MOV or metal oxide varistor with a non-linear V/I relationship and thus its ability to suppress voltage surges.
A MOV contains a ceramic mass of zinc oxide grains, in a matrix of other metal oxides (such as small amounts of bismuth, cobalt, manganese) sandwiched between two metal plates (the electrodes). Source: http://www.electroschematics.com/5224/metal-oxide-varistor/
MOV's, metal oxide varistors are components that have what characteristic? Keith H. Sueker, Power Electronics Design, 2005 PP 35 (NC set: transients)
A nonlinear V/I characteristic
Explanation: When exposed to high transient voltage, the MOV clamps voltage to a safe level. A metal oxide varistor absorbs potentially destructive energy and dissipates it as heat, thus protecting vulnerable circuit components and preventing system damage. Varistors can absorb part of a surge. Source: http://www.electroschematics.com/5224/metal-oxide-varistor/
Metal oxide Varistors of the types used for power electronics are made by pressing and sintering wafers of __________. Keith H. Sueker, Power Electronics Design, 2005 PP 37 (NC set: transients)
zinc oxide ceramic.
MOV's have a little power dissipation capability, and can experience what as a result of repetitive transients such as produced by SCR commutation? Keith H. Sueker, Power Electronics Design, 2005 PP 36 (NC set: transients)
Destruction
MOV are generally applied at their nominal RMS voltage rating and are expected to clamp transients to a peak voltage of _____ times their RMS rating. Keith H. Sueker, Power Electronics Design, 2005 PP 36 (NC set: transients)
(formula) 2.5 for 2.5 times their RMS or 2.5(.707x peak voltage). RMS is Root Means Squared and also the same heating effect AC as it’s DC counterpart.
The best protection from line-induced transients of all types on secondaries is? Keith H. Sueker, Power Electronics Design, 2005 PP 58 (NC set: transients)
A set of MOVs
Common-mode voltages (voltage to ground) can be effectively stopped at a transformer by what? Keith H. Sueker, Power Electronics Design, 2005 PP 58 (NC set: transients)
Also called what? PP 58 (NC set: transients)
An electrostatic shield between the windings.
A Faraday screen
Dry type transformers should be equipped with at least what on medium voltage circuits to avoid transient over voltage issues? Keith H. Sueker, Power Electronics Design, 2005 PP 58 (NC set: transients)
Distribution-class lightning arrestors.
Most gate drives for SCRs (Silicone Controlled Rectifiers) or insulated gate bipolar transistors (IGBT’s) are supplied in one way or another through the transformers with primaries at what potential and secondaries at what voltage? Keith H. Sueker, Power Electronics Design, 2005 PP 58 (NC set: transients)
With primaries at control circuit potential and secondaries at the cathode or emitter voltage.
Transformers have ________ that will couple the power voltage transients on the semiconductors to the low-voltage control circuits. Keith H. Sueker, Power Electronics Design, 2005 PP 58 (NC set: transients)
interwinding capacitances.
The best protection to transient over voltages through printed circuit board traces is what? Keith H. Sueker, Power Electronics Design, 2005 PP 58 (NC set: transients)
To equip the gate drive transformers with electrostatic shields and to be sure their primaries are tied directly to ground whenever possible.
Ground, common, and powers leads entering and exiting a PC board should be located where? Keith H. Sueker, Power Electronics Design, 2005 PP 59 (NC set: transients)
on the same end if possible, due to inductance ground planes.
The operating coils on contactors and power relays will generate what when they are de-energized? Keith H. Sueker, Power Electronics Design, 2005 PP 59 (NC set: transients)
transient voltages, or inductive kick.
Regarding transients and power relays, what on the coils will reduce the effect on other circuit elements? Define this. Keith H. Sueker, Power Electronics Design, 2005 PP 59 (NC set: transients)
R/C snubbers. : A simple RC snubber uses a small resistor (R) in series with a small capacitor (C). An appropriately-designed RC snubber can be used with either DC or AC loads. This sort of snubber is commonly used with inductive loads such as electric motors.
Signal circuit should be further protected by using shielding wire, the shields should be continuously connected but they should be grounded only at what point? Keith H. Sueker, Power Electronics Design, 2005 PP 59 (NC set: transients)
Only at a single point that serves as a earth ground for all signal commons.
If the signal lead is routed along the ground paths what happens to ground-loop? Keith H. Sueker, Power Electronics Design, 2005 PP 59 (NC set: transients)
The loop is eliminated.
What is the relationship between shielding electrostatic effects and electromagnetic coupling? Keith H. Sueker, Power Electronics Design, 2005 PP 60 (NC set: transients)
What is the answer to electromagnetic coupling? Keith H. Sueker, Power Electronics Design, 2005 PP 60 (NC set: transients)
Shielding Can Eliminate electro-static effects but it does little to prevent electromagnetic couplings.
Twisted pairs are the answer.
What can switching currents in semi conductors cause? Keith H. Sueker, Power Electronics Design, 2005 PP60 (NC set: transients)
Switching currents and semi conductors can cause very high DI/DT (Developed current/developed time) levels particularly in IGBT's (insulated gate bipolar transistors) and these transients can couple to other circuitry gate drives, and low-level circuitry should be kept away from power switching circuits.
What will drop the source voltage to zero in a microsecond or so and hold it there regarding SER's? Keith H. Sueker, Power Electronics Design, 2005 PP 60 (NC set: transients)
Commutation period.
The commutation period: dropping the source voltage to zero in a microsecond or so and holding it there until the commutation is completed is in effect called what? Keith H. Sueker, Power Electronics Design, 2005 PP60 (NC set: transients)
Notching
Notching is a disturbance that can propagate to other equipment in the area through what? Keith H. Sueker, Power Electronics Design, 2005 PP 60 (NC set: transients)
One way to reduce notching is to install what on the power lines? Keith H. Sueker, Power Electronics Design, 2005 PP 60 (NC set: transients)
Common power lines
R/C snubbers
Most but not all transients are associated with what? Keith H. Sueker, Power Electronics Design, 2005 PP 60 (NC set: transients)
Rising voltages, but falling voltages can also interrupt operation.
If the control transformer is supplying power to large contactor coils or fan motors the inrush current may cause what over relays or operations? Keith H. Sueker, Power Electronics Design, 2005 PP 60 (NC set: transients)
The voltage loss sufficient to drop relays or disrupt operations.
The cure to inrush current causing the voltage loss sufficient to drop relays or disrupt operations is what? Keith H. Sueker, Power Electronics Design, 2005 PP 60 (NC set: transients)
To oversize the control transformer or use low-leakage reactance design so that the control voltage can be held above the required minimum.
Name three signal processing electronic components. Keith H. Sueker, Power Electronics Design, 2005 PP 61 (NC set: transients)
Signal processing electronic components have a limited ability to reject what on differential inputs Keith H. Sueker, Power Electronics Design, 2005 PP 61 (NC set: transients)
Opamps, digital processors, and multipliers.
Common mode noise on differential inputs.
A circuit is presumably immune to high-frequency noise because of _______ of the multiplier. Keith H. Sueker, Power Electronics Design, 2005 PP 61 (NC set: transients)
Because of the common mode rejection of the multiplier
If a noise level is not really known it is a good idea to install what ahead of each multiplier input? Keith H. Sueker, Power Electronics Design, 2005 PP 61 (NC set: transients)
Pole of rolloff: A low pass filter
EMI or electromagnetic interference is defined levels for both _____________levels. Keith H. Sueker, Power Electronics Design, 2005 PP 61 (NC set: transients)
Radiated and Conducted levels
Regarding an unknown noise level and installing a poll of rolloff Ahead of each multiplier input, the pole should be located about how far above the highest frequency that the multipliers expected to pass?Keith H. Sueker, Power Electronics Design, 2005 PP 61 (NC set: transients)
A decade.
Radiated interference into and out of equipment can usually be thwarted by good grounding techniques and shielding of critical circuits. Interference conducted by supply control or load wiring may require the installation of what to reduce conducting noise in both directions into it out of the equipment? Keith H. Sueker, Power Electronics Design, 2005 PP 61 (NC set: transients)
A T-filter
Re: EMI and instrumentation what is often used to measure DC current levels and occasionally for AC? Keith H. Sueker, Power Electronics Design, 2005 PP 62 (NC set: transients)
Shunts: In electronics, a shunt is a device which allows electric current to pass around another point in the circuit by creating a low resistance path.
Regarding EMI problems with instrumentation what is used to amplify the shunt output voltage that is usually in the 50 to 100 mV range? Keith H. Sueker, Power Electronics Design, 2005 PP 62 (NC set: transients)
Isolation amplifiers.
informational: Isolation amplifiers are a form of differential amplifier that allow measurement of small signals in the presence of a high common mode voltage by providing electrical isolation and an electrical safety barrier. Isolation amplifiers are used in medical instruments to ensure isolation of a patient from power supply leakage current.[1]
What is also known as an isolation amplifier? source: http://www.learningaboutelectronics.com/Articles/Isolation-amplifier
Also called a unity-gain amplifier, this is an op-amp circuit which provides isolation of one part of a circuit from another, so that power is not used, drawn, or wasted in a part of the circuit.
The purpose of an isolation amplifier isn’t to amplify the signal. So what happens to the voltage?
The same signal that is input into the op amp gets passed out exactly the same. This means that output voltage is the same exact as the input voltage, meaning if 10V AC is input into a circuit, 10V AC is output. An op amp is a device with a very high input impedance. This high input impedance is how it causes isolation.
Difficulties may arise if care is not taken with what in regards to the shunt especially if the power circuit has a high ripple level? see figure below. Keith H. Sueker, Power Electronics Design, 2005 PP 62 (NC set: transients)
Lead dress.
The shunt should be made such that the terminals are symmetric about what of the shunt? Keith H. Sueker, Power Electronics Design, 2005 PP 62 (NC set: transients)
Symmetric about the geometric center of the shunt.
Contaminating signals can be neutralized with what of a few turns connected in series with what to shunt output? Keith H. Sueker, Power Electronics Design, 2005 PP 62 (NC set: transients)
Air core "pick up” coil.
Informational:
Its inductance is unaffected by the current it carries. This contrasts with the situation with coils using ferromagnetic cores whose inductance tends to reach a peak at moderate field strengths before dropping towards zero as saturation approaches. Sometimes non-linearity in the magnetization curve can be tolerated; for example in switching converters. In circuits such as audio cross over networks in hi-fi speaker systems you must avoid distortion; then you need an air coil. Most radio transmitters rely on air coils to prevent the production of harmonics. Source: http://info.ee.surrey.ac.uk/Workshop/advice/coils/air_coils.html
The precautions on shunt metering apply also to oscilloscope measurements of low-level signals in the presence of interference the ground lead of the scope should be looped back and forth along ________ to minimize loop area and the resultant induced voltages. Keith H. Sueker, Power Electronics Design, 2005 PP 63 (NC set: transients)
Back and forth along the probe.
it is important to note that three-phase transformers with Delta-connected primaries when connected to a 30, 4-wire supply system do not utilize? (NC set transformer connections) source: http://www.federalpacific.com/university/transbasics/chapter3.html
The 4th wire or neutral.
A wye system is also known as what? Transformer Principle and Applications, 2006: Transformer Connections, WB PP 23
A wye system is also known as a star system.
A wye to delta connection may be made with what in leu of one delta transformer to increase reliability and maintain voltage in case of one phase loss? Transformer Principle and Applications, 2006: Transformer Connections, WB PP 23
think of an alternative to a delta transformer in a situation where 3 phase undergrounded delta power is needed.
Three single phase transformers to create a delta bank.
Wye to delta connected transformers, with properly marked leads, always have an angular phase displacement of _________? Transformer Principle and Applications, 2006: Transformer Connections, WB PP 23
This does not imply use of a nuetral.
30 degrees voltage vector in a Delta ALWAYS; whereas, a 120 degree phase displacement (voltage vector and not current) only occurs on a wye or a high leg delta to ground.
A _______ connection may also be called a V connection because only two transformers on a delta bank are included. Transformer Principle and Applications, 2006: Transformer Connections, WB PP 23
Open Delta.
The voltage tolerance on most motors is plus minus what voltage in a percentage? Transformer Principle and Applications, 2006: Transformer Connections, WB PP 23
10 percent.
Today, the majority of dwellings are wired with a how many wire service? Transformer Principle and Applications, 2006: Transformer Connections, WB PP 23
the number of wires is just that, wires: not current carrying conductors necessarily.
Three wires: 2 wire and a messenger; where two phase conductors create a single phase service.
Transformer polarity refers to what? Transformer Principle and Applications, 2006: Transformer Connections, WB PP 24
The voltage-vector relationship of the transformer leads as brought outside the case. voltage vector means degrees of phase shift. Delta is 30° voltage vector displacement. Unless Line to Nuetral in a high leg then it is 120° .
Single phase transformer polarity is additive and subtractive when? Transformer Principle and Applications, 2006: Transformer Connections, PP 73
subtractive when h1 and x1 are adjacent and additive when diagonal.
h1 h2 h1 h2
x1 x2 x2 x1
subt add
What must be done when the transformer secondary taps are not positively identified? Transformer Principle and Applications, 2006: Transformer Connections, PP 73
The transformer must be tested to determine the correct polarity. Tech Fact. A transformer comparison to another identical transformer can be done as well.
In a Delta what is the winding voltage from phase A,B, & C with a standard Delta and no high leg center tap? Electrical field reference manual, PP 414
480V if it is a standard Delta.
What simplifies the task of connecting transformers in parallel? Transformer Principle and Applications, 2006: Transformer Connections, PP 74
The H1 lead is normally brought out on the right-hand side of the transformer case when facing the high voltage side. Notice this is the case on the Delta/ Wye transformer below regarding the data plate.
Methods used to test for polarity and check transformer lead markings include what? Transformer Principle and Applications, 2006: Transformer Connections, PP 74
Transformer comparison,
DC use, and...
AC use.
Instrument Transformers (PT's and CT's) and large substation transformers are ________Polarity, so the H1 and X1 Bushings will be on the what side of the transformer?
Instrument Transformers (PT's and CT's) and large substation transformers are Subtractive Polarity, so the H1 and X1 Bushings will be on the same side of the transformer. It is worth noting that on a 37.5MVA substation transformer where the primary and secondary are on opposite sides. the primary is 161KV and the secondary is 13,800V. Subtractive is not adjacent.
What is the difference between phase and line voltage?
Line voltage is the voltage measured between any two lines in a three-phase circuit. Phase voltage is the voltage measured across a single component in a three-phase source or load. https://www.quora.com/What-is-difference-between-line-to-line-voltage-and-line-to-neutral-voltage
What is a chopper circuit?
In electronics, a chopper circuit is used to refer to numerous types of electronic switching devices and circuits used in power control and signal applications. A chopper is a device that converts fixed DC input to a variable DC output voltage directly.
A DC transformer is nicknamed the Chopper circuit.
In a Delta system, the winding (phase) current is actually _________ percent of the line current; in other words, the line current is equal to phase current times ________. Transformer Principle and Applications, 2006: Transformer Connections, PP 77
Phase voltage is the voltage measured across a single component in a three-phase source or load. Line current is the current through any one line between a three-phase source and load. Phase current is the current through any one component comprising a three-phase source or load
57.7 percent line current. and 1.73 x phase current. Phase current by definition is phase to nuetral.
(.577x208V=120V. 208 is 2 phases and a N.) Where 1.73x120=208V)
1.73
The square √3 is also 1.73. this is used in a 3 phase power system for what reason?
The line voltage is best though of as "line to line"
The square root of three is a magnitude multiplier that accompanies a 30 degree phase shift between line voltages and their respective phase (phase is to nuetral as opposed to a line voltage) voltages for a wye system, and line currents and their respective phase currents for a delta system that is a result of adding (or subtracting) two vectors that are equal in magnitude and 120 degrees apart.
what is different from a transformer primary and a stator in a polyphase motor? Transformer Principle and Applications, 2006: Transformer Connections, PP 78
Nothing.
note: except that the secondary does not rotate in a transformer.
What type of transformer describes the following statement: "The three ends can be safely connected at the neutral point because no voltage difference exists between them." Transformer Principle and Applications, 2006: Transformer Connections, PP 78
A Wye transformer. Also known as a star transformer.
In a WYE / Star:
the phase current (line to nuetral and not line to line) is equal to what? How far out of phase are the voltages? the primary and secondary are how far out of phase in a WYE?
The phase current is equal to the line current, and they are in phase. There is a phase separation of 30º between the line and phase voltage.
The 180º phase shift between the primary and secondary of the transformer is shown in the figure above. (applied voltage is 180 out of phase of the induced voltage!)
A Delta to Wye connected 3 phase system has how many volts on the primary and on the secondary phase to phase? Electrical Field Reference Manual, PP 415
Remember a phase voltage is phase to nuetral and line voltage is line to line.
The primary has 2400V or 480V line to line Secondary has 277V/480 or 120/208V with a nuetral across any phase (phase voltage and not line voltage). Used where a 4 wire secondary distribution system is desired.
Why do generators always provide a WYE output with larger generators?
Because the phase voltage (phase to nuetral) is 57.7% line voltage (line to line) and the current is KVAx1000/√3 (1.73)x E. this means the voltage for the stator would be very high, and so would current. this would mean a much more expensive build for winding insulation, etc.
In 3 phase power, a total of _____line leads are required if the three circuits are kept separate, from the generator to the apparatus using the current (remember generators are WYE output). This is impractical, so what is used? Transformer Principle and Applications, 2006: Transformer Connections, PP 76.
6, so a common wire are used. Aka grounded wires.
What provides a 120V/208V feeder for a panelboard? Transformer Principle and Applications, 2006: Transformer Connections, PP 81
regarding a 480v bus. An advantage of the Delta connection is higher reliability. If one of the three primary windings fails, the secondary will still produce full voltage on all three phases. The only requirement is that the remaining two phases must be able to carry the load
A dual-wound delta primary connected onto the 480V line to line bus (not phase to phase as phase is phase to nuetral by definition). No primary neutral, but the secondary neutral can be connected to a center tap to ground.
What is the advantage of a Delta power system? Especially for a primary delta in an installation where sustainability is required?
Remember: phase voltage is phase to nuetral. Think line to line; which is not line to nuetral.
An advantage of the Delta connection is higher reliability. If one of the three primary windings fails, the secondary will still produce full voltage on all three phases. The only requirement is that the remaining two phases must be able to carry the load
What is a synchronous condenser?
synchronous capacitor or synchronous compensator) is a device, identical to a synchronous motor, whose shaft is not connected to anything but spins freely.[1] Its purpose is not to convert electric power to mechanical power or vice versa, but to adjust conditions on the electric power transmission grid. Its field is controlled by a voltage regulator to either generate or absorb reactive power as needed to adjust the grid's voltage, or to improve power factor.
A third winding that is often used in power transformers to provide station power requirements or a tie with synchronous condensers is what? Transformer Principle and Applications, 2006: Transformer Connections, PP 82
Remember: there is an advantage to a tertiary winding. See next card.
A tertiary winding.
What is the advantage of a tertiary winding? A 3rd transformer (delta) between two wye transformers.
When the fault or short circuit occurs, high circulating current will flow through the primary and secondary winding. Because of that current , overheating of transformer is produced, but by using a tertiary winding we can avoid that overheating. Inductive reactance of tertiary winding can limit over current.
When is a Wye to Wye connection used? Transformer Principle and Applications, 2006: Transformer Connections, PP 82 A tertiary winding is used in a Wye to Wye connection for what purpose? Transformer Principle and Applications, 2006: Transformer Connections, PP 82
When tying together two high-voltage transmission systems of unequal voltage.
A wye to wye is used To suppress 3rd harmonics. (An odd numbered harmonic which adds to each other, although triplen harmonics, odd multiples of the third harmonic: 3, 9, 15th are only single phase load related) May cause transformer overheating, overloaded neutrals, telephone interference.
Disadvantages of a wye-to-wye connection include what? Transformer Principle and Applications, 2006: Transformer Connections, PP 82.
what is used to limit this issue?
Harmonics.
A K series isolation transformer (rated K4-K20) and is simply a series transformer.
In a Wye to Wye connection the voltage of each single-phase unit connected to form a wye-to-wye connection is _____percent of the line phase (to nuetral) voltage: an advantage. Transformer Principle and Applications, 2006: Transformer Connections, PP 83
Remember: a WYE is either 120/208 or 277/480. The lower voltage always has a N.
57.7 percent
example 120 is 57.7% of 208. And 277 is 57.7% of 480V.
Delta to Delta systems are used where? Transformer Principle and Applications, 2006: Transformer Connections, PP 85
In industry where old equipment is used on new high-voltage 480 V bus duct systems. To answer in industrial settings is sufficient.
What is more common in an industrial setting.... a three phase system or three single phase units? Transformer Principle and Applications, 2006: Transformer Connections, PP 85
Three single phase units in an industrial delta to delta system. This allows the full voltage on the secondary with only 2/3 line voltages available.
One of the disadvantages of a Delta to Delta connected system is what? Transformer Principle and Applications, 2006: Transformer Connections, PP 86
To obtain a grounded system, what must be done? PP 87
The absence of an intentional connection to ground on the secondary of the transformer.
One of the corner of the delta secondary must be grounded.
what is the voltage on a corner grounded Delta transformer?
Always 480V.
When a Delta to Delta system has no neutral, and one is derived to give a reference to ground, this system is also referred to as what type of transformer? Transformer Principle and Applications, 2006: Transformer Connections, PP 87
grounded B phase. Which is also a hi leg. Wild leg. A 3 phase 4 wire Delta is another answer.
Which is a center grounded delta, but also derives a neutral. Versus corner grounded. The big difference from a WYE is a grounded b phase provides 208volts, and also a 480 option.
In a Delta to Delta grounded B phase system the center conductor is identified as what? What must be done with fusing. Transformer Principle and Applications, 2006: Transformer Connections, PP 87
Is identified AS what, not how is it identified.
As a neutral(not a grounded because it carries unbalanced current) conductor, and fusible clips must have a shunt, usually a copper tube, installed if used as a serviceable disconnect.
the voltage vector relationship of an open delta is what?
Line voltage displacement is 120°. With a 30° displacement for current.
the vectors form a closed loop with the sum of the three voltages adding up to zero. This is basic mechanism of ‘deriving’ the third phase by using only two transformers.
The KVA required for an open delta on the primary versus the secondary is what?
The combined transformer kVA has to be 115% of the load kVA.
This means an open delta transformer will only be able to deliver 57.7% of the capacity of an equivalent three phase delta transformer with similar voltage and load current.
A transformer configuration that allows for low cost install for future expansion is what? Transformer Principle and Applications, 2006: Transformer Connections, PP 88
The primary on an Open Delta is _____volts and the secondary is ______volts. With a voltage vector relationship of 60 degrees. Transformer Principle and Applications, 2006: Transformer Connections, PP 88
An open delta, or two single phase transformers.
Primary voltage is 2400V and the secondary voltage is 240 volts with a voltage vector relationship at 60 degrees.
What type of connection makes it possible to maintain operation in an emergency? Transformer Principle and Applications, 2006: Transformer Connections, PP 89
An open delta connection.
The load on an open delta must be reduced by how much from that of a closed delta. Transformer Principle and Applications, 2006: Transformer Connections, PP 89
42.3 percent. Since an open delta has to limit the load by 57.7%. Remember that a closed delta has a line and phase current difference but the open does not. You can remember this by picturing the phase angle displacement. Two windings are equal and three are 120 degrees apart.
One of the more popular Delta to Delta connections is the ________. Transformer Principle and Applications, 2006: Transformer Connections, PP 89
The advantage of a hi-leg to ground is what?
120/240V 4 wire system with high leg to ground.
120/240V versus 120/208V which is not adequate for 240 volt motors having a voltage tolerance of +/- 10 percent. Low voltage will result in overheating.
A wye to wye connection may have an angular-phase displacement of ______ or _____ degrees. Transformer Principle and Applications, 2006: Transformer Connections, PP 91
0 or 180 degrees.
A Wye to Delta connection always has an angular phase displacement of _____ degrees, with properly marked leads. Transformer Principle and Applications, 2006: Transformer Connections, PP 91
30 degrees.
A disadvantage of a delta connection is? Transformer Principle and Applications, 2006: Transformer Connections, Chapter 4 summary
Remember a Wye to Wye has the advantage of transforming to higher and unequal voltages.
that the coil is rated for the line voltage and thus makes the high voltage required for transmission difficult.
lower voltage-to-ground combined with the higher phase-to-phase voltage for long-distance power distribution.
What does the 30 degree difference in phase displacement mean regarding a wye to delta / delta to wye transformers on the same feeder? Transformer Principle and Applications, 2006: Transformer Connections, Chapter 4 summary
phase is not to nuetral. phase is phase to phase. Line is line to nuetral.
It means it is impossible to parallel a wye and delta transformer on the same feeder.
What makes it difficult to maintain good balance from phase-to-phase in a wye connection? Transformer Principle and Applications, 2006: Transformer Connections, Chapter 4 summary.
The ability to take single phase loads from line to neutral in a wye connection make it difficult to maintain good balance from phase-to-phase. Note: this is why a WYE panelboard will have all 3 phases balanced in a panel schedule.
There are 4 IEC1010 measurement categories, from low to high voltage, what are they and what system types do they apply to? PP26 test instruments NJATC 2008
phase 4 is closest to the utility
Cat I: electronic; any high-voltage, low energy source derived from a high-winding-resistance transformer, such as the high-voltage section of a copier
Cat IV: 3 phase at utility connections, or any outdoor conductors
Grounding in electrical construction is accomplished by connecting the circuit to what?
1. metal underground pipe
2. metal frame of a building
3. concrete encased 4. electrode (Ufor)
5. ground ring
PP30 test instruments NJATC 2008
What is magnetic field coupling also refered to as? PP18 test instruments NJATC 2008
Noise. this is because it is mutual iduction between 2 signal wires.
The true RMS test instrument is best suited for measuring with what equipment? PP44
Solid State components
variable frequency drives (VFD)
programmable logic controller (PLC)
The neon test light is the most common type and must not be used to test what? Why? PP44
A GGCI, becuase it does not draw enough current to trip the GFCI, since the resistance is so high.
A voltage indicator (inductive tester or tic tracer) will not indicate a voltage if the cable is what? PP48
shielded
List three types of configurations of the solar array and the most common type. PP 4
Utility supplemental and standalone. The most common configuration is a utility connected system
Find the inverse square law as relates to photovoltaics. Pp 31
A physical law that states that the amounts of radiation at points are proportional to the inverse of the square of their distances from the source.
Defined distributed generation. PP 26
A system in which many smaller powergenerating systems create electrical power near the point of consumption.
PV systems operating in parallel with the utility system, referred to as what systems? WB PP 1
Multimodal, distributed, interactive, or stand alone?
interactive
PV systems operated independently of other power systems are, referred to as what type of systems? WB PP 1
stand-alone
While PV cells produce only _______ power, PV systems can produce ______ power. WB PP 2
Cells produced DC power and PV systems can produce AC power
Balance of system (BOS) components typically include all but what? WB PP 2
PV modules and inverters.
List of three main components of the electric utility system. WB PP 3 photovoltaics
Generation, transmission, and distribution
The first practical Silicon solar cell was made in what year? WB PP 4
1954
Solar power and solar energy is commonly expressed in what units? WB PP 5
Solar power is commonly expressed in watts per square meter Solar energy is commonly expressed in watt hours per square meter.
Note:solar power is used to estimate the output of the PV modules and arrays over time.
What is the formula for solar radiance on the surface involving time? WB PP 6 (Photovotaic notecard set)
H = (E average) x T
Where H = solar radiation in watt hours per meter squared
E average = average solar radiation and watts per meter squared and
T = time in hours
The peak solar radiance incident on the earths surface is approximately what percentage of extraterrestrial irradiance? WB PP 7 (Photovotaic notecard set)
73%
List three atmospheric effects on solar radiation. WB PP 7 (Photovotaic notecard set)
Scattering, reflection, and absorption
Air mass is a representation of what? WB PP 8 (Photovotaic notecard set)
What value of Air mass is considered representative of average terrestrial conditions in United States and used as a reference condition rating modules and arrays?
Relative distance of atmosphere that radiation must travel through to reach the earth's surface
AM 1.5
What three components of the electromagnetic spectrum are contained in solar radiation? WB PP 9 (Photovotaic notecard set)
Ultraviolet, invisible, and infrared.
The orientation of PV arrays is defined by their what? WB PP 15 (Photovotaic notecard set)
Array tilt and array azimuth
To maximize wintertime output PV arrays are generally tilted at an angle close to what? WB PP 15 (Photovotaic notecard set)
Lattitude + 15 degrees
What is the formula for roof slope angle? WB PP 23 (Photovotaic notecard set)
Theta (angle) = Tan-(Rise/ Run)
What is a monopole array? PP 155 (Photovotaic notecard set)
An array that has one positive terminal and one negative terminal
What is a bipolar array? PP 155 (Photovotaic notecard set)
A bipolar array is an array tha has two terminals, one positive and one negative, and a third terminal connected at a center tap.
What is a Photovoltaic effect? PP 154 (Photovotaic notecard set)
A photovoltaic effect is the movement of electrons within a material when it abords photons with energy above a certain level.
The maximum power voltage (Vmp) and maximum power current (Imp) both share what definition? PP 155 (Photovotaic notecard set)
is the operating voltage/ current on an I-V curve where the power output is at maximum.
A p-type semiconductor is a semiconductor that has what? PP 154 (Photovotaic notecard set)
A p-type semiconductor is a semiconductor that has electrond voids.
An N-type semiconductor is a semiconductor that has what? PP 154 (Photovotaic notecard set)
An N-type semiconductor is a semiconductor that has free electrons.
Bypass diodes do what for a PV device and under what condition or why? PP 154 (Photovotaic notecard set)
Bypass diodes protect PV devices form damage and excessive loss of power by directing current around shaded or damaged devices. Remember: Voltage is additive in series and thus current is constant, and since sunlight is directly proportional to current production then a shaded panel would have lower current and would become a load. resulting in damage.
What affects the magnitude and postion of the I-V curve? PP 154 (Photovotaic notecard set)
solar irradiance and cell temperature.
Bypass diodes are typically installed around groups of _____ to ______ series-connected cells. PP 148 (Photovotaic notecard set)
Bypass diodes are typically installed around groups of 12 to 18 series-connected cells.
Note:bypass diodes must be able to handle the maximum operating voltage for the number of cells or modules bypassed, and must be rated in excess of the maximum circuit current.
Define a bypass diode. PP 148 (Photovotaic notecard set)
A bypass diode is a diode used to pass current around, rather than through, a group of PV cells.
A bypass diode allows a reverse bias of only ______ volts. PP 148 (Photovotaic notecard set)
.7 volts
Most modules are rated for a maximum system voltage of ______, though some are rated as high as _______. PP 148 (Photovotaic notecard set)
600v
1000v
What should be remembered about PV devices and thier current rating regarding connection in series? PP 144 (Photovotaic notecard set)
It should always be remembered that PV devices of different current rating should never be connected is series since "...the current output for a circuit of disssimilar devices in series is limited to the current of the lowest-current output devide in the entire string."
What should you remember about the juction box on a PV module if available? PP 144 (Photovotaic notecard set)
That the PV module may be configured for the ability to change the series or parallel configuration with certain jumper arrangements.
The top and bottom surface of a PV cell or module is of what type of silicon junction and polarity? PP 144 (Photovotaic notecard set)
The top is negative (N type) and the bottom is positive (p type). PP 126
Concerning the photo voltaic effect, what is associated with shorter wavelengths and higher freqeuncies? PP 125 (Photovotaic notecard set)
Higher energy.
Finish the sentence: The absence of a negative charge is considered a ___________. PP 124 (Photovotaic notecard set)
positive charge carrier.
A rectifier converts? PP 120 (Photovotaic notecard set)
A converter....
An inverter....
A rectifier converts AC to DC.
A converter converts a AC voltage to a different voltage level.
An inverter converts DC power to AC power.
Define a type of standalone system where the output of the PV module or array is directly connected to the DC load. PP 120 (photovoltaic notecard set)
A direct coupled PV system.
Define an electro-chemical device that uses electricity to split water into hydrogen and oxygen PP 120 (photovoltaic notecard set)
An electrolyzer
What is Islanding? PP 120 (Photovotaic notecard set)
Islanding is the undesirable conditions where a distributed generation power source, such as a PV system, continues to transfer power to the utility grid during a utility outage.
Define a multi-mode system. PP 120 (Photovotaic notecard set)
A multi-mode system is a PV system that can operate in either utility interactive or standalone mode and uses battery storage.
Concerning net metering, using this system, energy supplying the utility PV system is? PP 113 (Photovotaic notecard set)
effectively credited to the customer.
What type of PV system is the simplest and least expensive PV system that produces AC power because they require the least components and do not use batteries? PP 113
The utility interactive system that operates in parallel with and is connected to the electric utility grid.
Utility interactive inverter output is determined by what? Whereas the output from battery based inverters, is determined by what? PP 102 (Photovotaic notecard set)
Utility interactive inverter output is determined by the DC input from the array unlike the output from battery based inverters, which is determined by the load.
What type of inverter is used exlusively in PV systems?
think of what type of UPS is used with DC batteries
static inverters. PP 224 (Photovotaic notecard set) A static inverter is a device that converts a dc voltage to a stable ac voltage for use in an uninterruptible power system.
inverters for PV systems are broadly classified as what? PP 226 (Photovotaic notecard set)
Think one grid tied or not
either stand alone or interactive.
What size are String inverters, central inverters, and utility scale inverters? PP 227 (Photovotaic notecard set)
String inverters: small 1kw to 12 kw residential
central inverters: large utility interactive 30kw-500kw
utility scale inverters: very large 500kw-1MW and bigger
For a stand alone PV system what determines the inverter's power rating? PP 226 (Photovotaic notecard set)
The AC load rather than the DC power source.
What is provided on heat trace for monitoring?
Both an isolated solid-state triac relay and a dry contact relay are provided for alarm annunciation back to a Building Management System. (BMS)
Heat trace is an important component of freeze protection on piping. What must be used to comply with the requirements of Thermal Management, agency certifications, and NEC, along each heating cable branch circuit?
Ground Fault Equipment Protection.
what is not allowed on the job for hangers and supports for HVAC and piping equipment?
powder actuated fasteners are N/A job.
Another term for a pear hanger is what?
A ring hanger, versus a clevis hanger which wraps only half of the pipe. 6_23-529.00 sub
A riser clamp can have what type of finish?
not plain, but zinc coated per the submittal 230529.00
What is the spec for regarding sleeves through partitions, walls and floors?
For non-membrane walls galvanized cast iron, galvanized rigid steel with continuously welded center flange. Membrane waterproof walls and floors and roofs use O.Z. Gedney type WSKA or FSKA or equal.
Under basic materials and methods specifications section 26 00 50-22 G5 What is the conduit size and use in regards to bushings?
Terminate threaded conduits into threaded hubs or with locknuts on inside and outside of boxes or cabinets. Install bushings on conduits up to 1-1/4-inch trade size and insulated throat metal bushings on 1-1/2-inch trade size and larger conduits terminated with locknuts. Install insulated throat metal grounding bushings on service conduits or as indicated on the drawings.
Under specifications for basic materials and methods, what should be done with conduits that are un-used?
Per spec 26 00 50-22 G8 Cap all unused conduits and identify destination point.
Under specifications for basic materials and methods, what should be done with the ends of all conduits at a minimum?
G10 under 26 00 50-22 All conduit ends to have insulated bushings.
Per specifications 26 00 60-6 Grounding and Bonding 3.2 D states what about bonding and grounding conductors in metallic raceways?
Bond at each end all grounding conductors routed in metallic conduit by using grounding bushings.
The common point on a 4-wire, three-phase, 120/208V wye-connected system is defined by the Code as the “________.”
Neutral point. MikeHolt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 NEC PP 55 Question 33
Output watts uses what formula? PP. 101 Mike Holts 2014 “Exam Preparation”. There are two formulas.
watts= HP/746; whereas, output watts accounts for losses.. INPUT WATTS/EFFICIENCY is correct.
OUTPUT IS NOT THE INPUT WATTS.
If you wanted to know the Apparent Power and you know the wattage and the power factor, how would this be expressed in a formula?
Mike Holts Exam Preparation 2014 PP 83
KW/PF=APPARENT POWER
Efficiency would be figured out how?
OUTPUT WATTS/ INPUT WATTS=EFFICIENCY. dividing smaller by larger numbers always give the percentages.
What is the input watts using watts and efficiency?
input would be a larger number than the output watts.
OUTPUT WATTS/ EFFECIENCY Remember when you divide, you will get a larger number.
If you know true power and power factor, can you know apparent power? And what would be the formula if you could.
Formulas used to determine the power factor are Power factor = watts/VA.... also R/Z and various other formulas are correct.
PP 19 2017 Journeyman Electrician Exam Questions and Study Guide, Brown Technical Books: Ray Holder.
One way to find I when all you know is KVA and E in a 3 phase circuit is?
P/E(1.732)=I is another way of viewing this formula
I = VA/(volts x 1.732) PP 21 2017 Journeyman Electrician Exam Questions and Study Guide, Brown Technical Books: Ray Holder.
True power (watts) equals apparent power (VA) in an electrical circuit or load containing only?
True power (watts) equals apparent power (VA) in an electrical circuit or load containing only resistance.
PP 22 2017 Journeyman Electrician Exam Questions and Study Guide, Brown Technical Books: Ray Holder.
The true power (watts) of a single-phase circuit or load that contains inductance or capacitance can be calculated by the use of the following formula:
TP= (KVA x PF)
PP 23 2017 Journeyman Electrician Exam Questions and Study Guide, Brown Technical Books: Ray Holder.
Describe the PF triangle. PP 23 2017 Journeyman Electrician Exam Questions and Study Guide, Brown Technical Books: Ray Holder.
Rememember that P/E=I. So it makes sense that W/VA=PF
Much like the formula to find over current protection for a load, (load/ correction factor), the formula for Number of Circuits is what?when you know VA?
LOAD VA / CIRCUIT VA= # of CIRCUITS.
PP 37 2017 Journeyman Electrician Exam Questions and Study Guide, Brown Technical Books: Ray Holder.
To find amps when KVA is known you use what formula? for single phase.
similar to the resistive or single phase calculation where P/E=I.
(KVAx1000)/E =I.
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP11
How do you find amps when using 3 phase and you know the KVA?
similar to P/E=I for the standard formula without taking into account reactive loads and the 3 phases.
(KVAx1000)/Ex1.73
Questions and Study Guide- Ray Holder.PP11
In what NEC article do you find GFCI protection?
210.8 (if you answered 210 then that is fine)
What NEC article has demand factors for household cooking appliances?
article 220 has this for cooking appliances
The recommended voltage drop for a branch circuit is what percent? What about a feeder.
3%. Or 5% total for branch and feeders, which proposes an assumed 2% for feeders. Per the NEC.
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP16
What chapter 9 table in the NEC regards percent area of conduit and tubing?
Table 4 in chapter 9 covers this.
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP12
Which annex in the NEC is used for conductors all of the same size in conduit and tubing?
NEC table 9 annex C covers this.
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP12
Which annex of the NEC has examples of code calculations?
Annex D has this in the NEC as a reference.
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP12
what is the formula for KW in a 3 phase circuit when the voltage and current is known?
this is the same formula for both KW and KVA
[KW=I(E)x1.732]/1000
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP20
What is the formula for KVA or VA when the current and voltage is known for 3 phase electrical systems?
KVA=[IxEx1.732]/1000. Also I/Ex1.732 would suffice as this is simply VA and not KVA. Note: this is the same for KVA and KW.
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP20
What is the formula for P when E and I are known? In a reactive 3 phase system.
the use of 1.732 is consistent in all 3 phase formulas with the use of E. If this were resistive only then we use E....and in a reactive circuit you use VA instead of E.
P=VAx1.732. for 3 phase.
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP20.
The use of KW is in circuits that have reactive loads? T or F?
False: the resistive figure for all electric is KW and not KVA.
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP23
The true power (watts) of a single phase circuit or load that contains inductance or capacitance can be calculated by the use of the following formula.
remember that in a 3 phase system we use 1.732 next to E.
W=ExIxPF
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP23
the formula for the number of circuits is what? When you know the VA of the circuit and the load.
this is not the same as it is for commercial office buildings; such as, stores, banks, restaurants, etc.
LOAD VA/CIRCUIT VA= Number of circuits.
For commercial buildings we at 125% to the VA in this formula.
When calculating loads generally for systems what is the standard for various types of loads.
Think of continuous and non-continuous. Remeber there is an exception to this if it is a rated continous load.
the OCP can be determined using the 125% of the continuous (over 3 hours run time) and 100% of the non-continuous. (less than 3 hours run time.)
What is the exception for the 125% rating for a load that runs for more than 3 hours that allows a 100% rating of the OCP?
This exceptoinin 210.20(A) allow a load to have the OCP rated at 100% if the load is rated for continuous operation.
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP40
Are circuit breakers rated for continuous operation?
CB's are rated for continuous operation only at 400 amps or more.
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP40
Generally lighting loads will be supplied by what size OCP?
15 and 20 amperes CB's generally supply this type of load. Per NEC 210.23A
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP40
What table is used for lighting circuit load calculations?
Table 220.12 determines this using the outside square footage of a building, but does not include porches, garages, or unfinished spaces ADAPTABLE FOR FUTURE USE.
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP40
Lighting loads are considered continuous use or not as continuous use under what circumstances?
Think home versus a store and time of occupancy
Lighting loads for habitable spaces of dwelling units and hotels and motels is not considered continuous but for commercial and industrial they are.
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP42
When calculating branch circuits you do what similar to motor calculations?
Think of this: you cannot install part of a circuit breaker.
you must round up for this number of circuits calculation.
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP43
Multifamily dwelling units without cooking units are to be treated how?
This type of dwelling unit without cooking provisions is treated the same way as hotels and motels at 2VA per square foot. NEC220.12
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP43
The formula for determining the number of general lighting branch circuits in an office building is what?
[Load VA x 125%]/circuit VA=The number of circuits in this type of building.
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP43
when calculating the number of branch circuits for lighting needed in a commercial building like a mercantile, or showroom, what must be remembered?
think show room.
Not only does this type of occupancy require a 125% rated load, it must also take into account display, specialty, enhancement, or accent lighting in addition to the general lighting.
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP44
When determining the amount of VA for banks and office building when the number of general purpose outlets to be installed has not been determined, what must be done for the purpose of calculations?
remember that commercial buildings are large and usually require a very conservative outlet number: non-dwelling will be at 180VA per square foot but this is the exception.
In this type of building when the number of general purpose outlets are not yet determined, you must add 1VA per square foot to the building calculation per 220.14K and fine print not B in the table. Or as calculated under 220.14I.
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP44
What is the formula used for a commercial building when the number of receptacles are known?
number of circuits=[180VA x number of receps]/circuit VA.
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP46.
How many receptacle are required for 14 linear feet of show window?
remember the linear foot calculation method for show windows is [200VAx linear ft. x 125%]/circuit VA. This is similar to load VA/ circuit VA.
2. The NEC 210.62 requires one outlet per 12 linear feet. However this requires the linear foot method calculation.
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP46.
What type of cord connected equipment is used to determine the number of branch circuits for multi-outlet assemblies installed in commercial, industrial, and educational locations?
The cord-connected equipment that is expected to be used at the same time per NEC 220.14H is used to determine this number.
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP46
the formula for calculating the required branch-circuits for fixed multi-outlet assemblies where the cord-connected appliances are unlikely to be used simultaneously, you can use what formula?
number of circuits=[(linear ft./5)x180VA]/circuit VA. where outlets are unlikely to be used at the same time.
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP46
To calculate the branch circuits required for fixed multi-outlet assemblies where the cord connected appliances are likely to be used simultaneously, what formula may be used?
think banks and office buildings.
number of circuits= [linear ft. x 180VA]\circuit VA. this formula is used for simultaneous loads in a commercial buildings such as a bank or office building.
What is the minimum and maximum size of a circuit breaker for other than individual branch circuits?
15-50 amps. Versus individual branch circuits that allow 60 amps or more and start at 25amps.
Source: 2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP48
We round up for other than multi outlet circuits until what amperage of over current protection is exceeded, per NEC 240.4B1(2)&(3).
As long as the next higher OCPD does not exceed 800 amps.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP 48.
Under what conditions do we round down for a branch circuit if the standard OCPD (over current protective device) does not correspond to a size fuse or breaker?
if the OCPD is over 800 amps we round down per NEC240.4(c)
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP48
When sizing branch-circuits and OCPD for appliances such as water heaters and cooktops, they are to be sized per NEC article?
422 versus household cooking appliances sized per table 220.55.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP48
What size water heater is considered non-continuous loads?
over 120 gallons and not 120 gallons or less.
per NEC. 422.13
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP48
Is overcurrent the same as ampacity?
No. Overcurrent is the over current protection; such as, a fuse or breaker where ampacity is the size of the feeders or conductors.
fixed electric space heating is what type of load? What article do we find this at?
continuous. And article 424 is where it can be found.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP49
Knowing how to find the number of branch circuits for lighting, how do you propose the formula would look to find the number of branch circuits for resistive heating?
Load VA x 125%/ circuit VA ... similar to lighting formula that uses the same calculation in office buildings where the lights are on for more than 3 hours at a time.
define the term demand factor.
Think temporary loads. Versus demand load.
ratio of maximum demand of a system/ total connected load.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP59
Define a demand load.
versus demand factor where not all of the loads are used at the same time.
demand load is the given demand at any given instance of a system or appliance.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP59.
Table 220.55 is used to size appliances of what size?
over 1.3/4 KW
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP60
Household cooking appliances rated 8.75KW or more are required to be supplied by at least a what size OCPD?
40amps.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP61
When the rating of a cooking appliance falls under both column A an B, you must do what?
You must use both columns A and B in table 220.55 and add them together if both columns apply.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP62
What happens if you have all ranges of the same size and over 12KW through 27KW?
remember if they are not all the same size we use note 2 column C of T220.55
We apply note 1 of column C and increase the demand value in column C by 5% for each KW that exceeds 12KW.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP63
When calculating demand facgors for ranges of unequal ratings of 8&3/4 through 27KW, when the nameplate rating of any range less than 12KW you are to use what? as a minimum and add the ratings together and divide to obtain the average? then apply note 1, per note 2 of T220.55.
12KW as a minimum if any one range is smaller than 12KW but greater than 8.75KW
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP65
When sizing branch-circuit loads for a single branch circuit supplying a counter mounted cooking unit and not more than 2 wall mounted ovens, it is permissible to do what?
It is permissable for 2 wall and 1 counter mounted cooking units to add all the nameplates and treat them as one range.
What happens with the nuetral sizing for dryers and cooking units at the feeder or service?
An extra 70% is permited as a demand factor per NEC 220.61(B)1.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP66
Does the 75% residential rule for 4 or more fastened in place appliances include space heaters, dryers, ranges, or air conditioning equipment?
Per NEC 220.53 note the 75% rule for residences does not include these but does include garbage disposers, sump pumps, garage door openers, attic fans, and anything else FASTENED IN PLACE.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP66
The demand factors in table_______ shall be permitted when sizing feeders and service entrance conductors for electric clothes dryers in residences.
T220.54 is used for this sizing.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP67
Each dryer shall be calculated at a minimum of _______________
5000VA or the nameplate, whichever is larger. 220.54.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP67
For commercial cooking related equipment, branch-circuits and ocpd are sized according to what?
The nameplate rating of the appliance is used to size branch circuit OCPD's in commercial settings.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP68
When sizing feeders and service conductors for commercial cooking equipment, we apply the demand factors in what table?
Table 220.56 is used for this in commercial feeder and service calculations for cooking equipment.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP68
What is called normal operating temperature in the NEC 310.14(B)16?
Remember: If the equipment is not marked, what must be remembered regarding derating for temperature and ampacity? If the equipment is not marked, it is 60 Celsius rated for 100 amps and less. �Note: Over 100 amps is 75 Celsius rated
this is the temperatures of 30 deg. C and 86 deg. F.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP81
If the termination's ampacity is not stated then we assume it is what temperature rating?
required ampacity = load/correction factor
in this scenario.
conductors must be sized to what temperature rating of what?
these must be sized to the lowest temperature rating of the wire, circuit breaker, terminal or device.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP85
Why might a higher temperature rating conductor be used on lower temperature rated terminations?
this may be done to account for derate in a conductor and ampacity or adjustment factors per 110.14C.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP85
If the termination's ampacity is not stated then we assume it is what temperature rating?
Remember: if the equipment is not marked at is under 100amps it is 60C and over 100 amps is 75C.
most terminations are rated at 60C or 75 degrees C.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP85
Many conductors are rated how? Example: THWN/THHN. How does this effect ampacity and derate.
This type of conductor is dual rated. ampacity is rated on the lower rating THWN 75C and the derating factor is rated on the higher THHN 90deg. C.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP86
How long must a raceway be to require ampacity derate?
Remember: 4 or more requires temperature derate as well as number of conductors requires derate.
more than 3 current carrying conductors in a raceway OR CABLE longer than 24 inches requires this.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP87
More than 3 current carrying conductors in the raceway or cable.... in an elevated ambient temperature and a raceway OR CABLE longer than 24 inches uses what formula?
required ampacity = load/temp.correction x adj. factor
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP88
the ampacity of a 3 wire single phase service and feeder conductors 100-400 amps must be rated how?
This must be rated at NOT LESS than 83% of the service or feeder rating.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP89
conductors ______inches or longer that are looped and unbroken are counted as what?
12 inches or longer are counted as two conductors for a single conductor.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP100.
If a conductor does not leave the box they are counted as how many conductors?
A domed luminaire is treated the same way
not counted as a conductor for this because it doesn't leave the box.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP100
table 314.16A is used to determine the minimum size box or the maximum number of conductors in that box when what condition is met?
This table is used to size a box when all the conductors are the SAME SIZE.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP101
table 314.16A does not account for devices or fittings for fill in the box. these cable clamps, support fittings, and devices are counted how?
All are counted as one device based on the largest wire size in the box, except devices, which count as two.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP101
equipment grounding conductors for box fill are counted as one conductor in the box, and we count this different for what systems with an additional EGC count?
Isolated systems are counted with one for the EGC and one more for the isolated system based on the largest EGC.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP101
For straight pulls the size of the box hall not be less than what?
8 times the trade diameter of the LARGEST raceway entering the box.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP103
According to NEC314 an angle U pull, the proper size junction box shall be what?
the largest raceway by 6 and add any additional conduits for this type of pull box.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP104
When determining the maximum number of conductors allowed in a standard trade size conduit or tubing all the same size, we use what table?
Chapter 9 table 1 is used for this type of conductor and conduit fill calc.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP104
What table is used for conductors of different sizes in conduit, tubing, or raceways?
Remember: table 5A is for compact aluminum conductors
Chapter 9 table 4,5,5A is used for these types of conductors in conduit, tubing, or raceways.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP105
Under Chapter 9 note 4, what is said?
that if the maximum length of a conduit or raceway does not exceed 24 inches, we shall be permitted to fill to 60% of their total cross sectional fill. Per this part of the NEC.
Do the equipment or grounding conductors get counted when calculating permitted conduit or raceway fill? Insulated and bare refer to what tables?
yes these get counted for raceway or conduit fill calculations.
Insulated is table 5 and bare is table 8 chapter 9.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP107
When calculating the maximum number of conductors, all of the same size or, permitted in a conduit or tubing, when the calculation results in a decimal of _______ or larger, what must be done?
.8 or larger requires an additional wire of the same size to be installed per Chapter 9 note 7.
in a gutter or wireway where splices and taps are NOT made, wires of the same size or different sizes shall not exceed what?
we disregard the length of the wireway or gutter.
20% of the cross section of the wireway or gutter shall not be exceeded where splices or taps are not made.
355.22(A)&(B), 376.22(A)
The K value for copper and aluminum is what?
K being the specific resistance is 12.9 ohms for copper and 21.2 ohms for aluminum.
The CM for a conductor is found where in the NEC?
Chapter 9 table 8 is where this can be found. AKA conductor properties.
What must be done to determine the cross sectional area of a conductor in KCMILS?
We must add 3 zeros for this cross sectional number size.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP124
The square root of 3 represents what in a 3 phase circuit?
This represents the conductor length in a 3 phase circuit.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP124
What is the formula for VD in a 3 phase circuit? single phase?
Remember: the 1.732 or 2 represents the length of the circuit.
The only difference between a single and 3 phase VD calculation formula is the use of 2 versus 1.732 for a 3 phase circuit. for the use of 1.732KLI/CM.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP124
A useful formula that may be used to size conductors in a 3 phase circuit to prevent excessive voltage drop is?
CM=[1.732xKxIxD]/VD
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP126
The following formula can be used to determine the approximate distance circuit conductors may be installed to prevent excessive voltage drop in a SINGLE PHASE CIRCUIT
D=[CMxVD]/2xKxI
Where D is distance.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP127
The following formula can be used to determine the approximate distance circuit conductors may be installed to prevent excessive voltage drop in a THREE PHASE CIRCUIT
D=[CMXVD]/2xKxI
3 phase circuit
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP127
The formula to determine the MAXIMUM LOAD when limiting VD on a single phase circuit is?
I=[CMxVD]/2xKxD
maximum load on a single phase circuit.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP127
The formula to determine the MAXIMUM LOAD when limiting VD on a three phase circuit is?
I=[CMxVD]/1.732xKxD
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP128
The ohms law method for determing the voltage drop of the conductor works for what type of circuit?
this formula only works for single phase circuits ONLY.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP129
regarding disconnecting means and OCP for continuous duty motors, what will be used?
typically the table 430.247 and 430.250 will be used.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP139
for motors less than 1200 RPM (low speed), hogh torque, and multipseed, which all may have higher than normal current, what must be used for the disconnect and OCPD?
in motors with higher current draws they use the nameplate, typically.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP139
motors, unless otherwise stated, or considered what type of load?
These are considered a continuous load unless stated otherwise.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP140
the actual conductor size for motors is found using table 310.15(B)16 or what other table?
table 400.5A is used to size conductors for these as well as the normal 310.15 tables.
Each motor and its accessories is required to have what components regarding protection?
these shall have
branch circuit,
short circuit,
and ground fault protection by the use of OCPD's such as fuses or circuit breakers.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP141
what table is used to size motor OCPD?
table 430.52 does this. they shall be sized no large than these percentage values.
what is known as initial sizing?
the use of table 430.52 for motor OCPD's sizing and 240.6 the fuse and breaker sizing in the NEC.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP141
When sizing OCPD for motors, if adjustable, what should they be set at?
the lowest possible adjustable setting is used for these to afford maximum protection.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP143
What is known as maximum or absolute sizing?
regarding motors, this is defined as going up to the next size OCPD to afford starting current as allowed by 430.53(C)(1) ex. 2.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP143
in general, to properly size the ocpd for feeders supplying two or more motors, the rules in 430.62A are?
no larger than the largest OCPD for any given motor, plus the sum of the flc of all other motors in the group.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP143
regarding feeders and barnch circuits for motors, what happens with OCPD sizing?
branch circuits size up and feeders round down.
continuous-duty motors of more than 1hp and automatically starting motors of less than 1hp are required to be protected in what way?
These type of motors are protected by overloads. 430.32A.
Overload devices for motors use what table for minimum and maximum based on what?
these are based on motor nameplates and tables 430.32A1 minimum and 430.32C maximum.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP144
What two pieces of information can be found where to size motor overloads?
The ampere trip rating of overloads is based on the service factor and temperature rise on the motor nameplates.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP144
if a motor has an integral thermal protector, the ultimate trip setting, in amps, shall not exceed the percentage values as expressed in what?
NEC 430.32A2 is used with this type of motor overload protection multiplied by the motors FLC as given in all the 430 tables.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP144
All motors must have a disconnecting means, and the ampere rating is not less than what % of FLC as given in table 430.248-250?
115% is the minimum rating of this for motors.
In what HP is the disconnect allowed to be a snap switch (rated in HP), breaker, or manual motor controller?
2HP-100HP is the range that allows this type of disconnect.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP145
for stationary motors of _______hp or less and _______volts or less, the disconnecting means is permitted to be an ac general use snap switch where the motor full load current rating is not more than 80% of the ampere rating of the switch.
2HP and 300 volts or less in this situation allow the disconnecting means to be this.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP146
If a dwelling does not have provisions for cooking, cleaning, and laundry.... what does this mean?
Without these 3 criteria, it cannot be considered a dwelling.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP156
in 310.15(B)7 of the NEC, for sizing a 3 wire single phase residence rated 100-400amps, the service conductors must have an ampacity not less than what?
83% minimum size for these at this location.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP157
When you do the optional method calculation for a residential service, you simply add and apply what?
for this method of calculating a residential service you simply add the nameplate values of the equipment together and apply one demand factor.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP157
Why would the minimum size service for a residence be 100amps?
because the ampacity fo the ungrounded conductors shall not be less than the rating of the service disconnecting means 230.42B and this service disconnect shall have a rating of not less than 100 amps. 230.79C
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP157
When applying t220.12 to a residence for the square footage, what must not be included?
remember: you would not spend alot of time in a garage, a porch, or enclosed area for future use and there would be little load.
We do not include the square footage of garages, open porches, and enclosed areas for this?
For a residential calculation a minimum of how many small appliance branch circuits are required? At what VA? and how many laundry circuits?
2 small appliance and 1 laundry at a minimum for this service calculation at 1500VA ea.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP158
Step 3 in a residential calculation is to apply what?
Step 1 is square footage, step 2 is applying 2 small appliance and one laundry at 1500VA, while step 3 is to apply the demand factors in T220.42 for these and lighting and receptacle loads.
Step 4 for a residential calculation is what?
apply a demand factor of 75% of the nameplate rating of 4 or more fastened in place appliances. (not electric ranges, clothes dryers, space heating, or air conditioning per 220.53)
What is step 5 in a residential calc? What must be remembered for the nuetral?
clothes dryer at 5kVA or nameplate, whichever is bigger. for each dryer. The nuetral may be 70% of the value found 220.61(B)1
When sizing cooking appliances for a residence what is added?
a further demand of 70% of the demand load on the ungrounded conductors may be applied to the nuetral grounded conductor. 220.61(B)1
Step 7 of the residencial calc is to determine the demand load for the fixed electric space heating or AC, where you are permitted to do what?
you may omitt the smaller of these two that are considered non-coincidental loads. 220.60
The 8th step of a residential calc is to add what percent of the largest motor?
25% of the largest motor is added to this calculation. Usually the AC unit.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP161
the final step in a residential calc is to add what?
this final step omitts the added VA of square footage, and 2 small appliance and laundry becuase this is captured in step 3 where these are applied the demand factors in T220.42 and the 2 small appliances and luandry are added to it.
In this calc, the final step is to add the VA of steps 3-9 and multiply by 83% and then size per ampacity tables and then the GEC per 250.66.
When using the optional method to calculate a residential calculation, the calculated load shall not be less than what percent of the first 10KW and the remainder of the general loads?
100% of the first 10kw and 40% of the remainder of the general loads.
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP164
A multi family dwelling is a unit containing what?
this definition says,"a building containing 3 or more dwelling units".
2017 Master Electrician Exam Questions and Study Guide- Ray Holder. PP180
How is the grade of a bolt determined? WB9
An SAE bolt thread size is determined by measuring what? WB9
By adding the number 2 to the number of hash marks on the bolt head
threads per inch
An ISO bolt thread size is determined by measuring what? WB10
mm form crest to crest
the length of a bolt is determined by measuring what? WB10
The length of the shaft
The formula for torque is what? WB1
Torque = length x force
The fastening process is comprised of four distinct phases. WB7
Run Down
Alignment
Elastic
Plastic (yield)
The total force required in a torque application is comprised of two distinct regions. What are they? WB6
Defined how?
Static breakaway torque
Dynamic applied torque
Static breakaway torque: the friction the fastener must overcome
Dynamic applied torque: the torque required to move or rotate the fastener after it has been seated
What is the 90/10 rule regarding friction? PP7
90% of torque is friction and 10% is stretch
The direction of the torque can be determined by using the right hand grip rule: ……which is?
if the fingers of the right hand are curled from the direction of the lever arm to the direction of the force, then the thumb points in the direction of the torque.[6]
Some estimate that adding a lubricant could reduce the required torque reading by up to? What %
40 percent
even though you can’t see it, a tightened bolt has been stretched a microscopic amount, and this stretch is called Tension.
Just like a stretched spring, which tends to pull back into its original shape, a stretched bolt tries to pull itself back to its normal state. It’s this pulling back force, called the “_______” that actually maintains the tightness of the joint.
clamp force
Note: But lubrication on the bolt threads—and a whole host of other factors—can cause fluctuation in torque readings. So once you add a lubricant of any kind to the threads, all bets are off as to whether the same torque setting will truly secure the bolt. That’s because nobody really knows how the lubricant affects the torque measurement on a bolt without performing a scientific study using expensive lab instruments.
Describe the benefits of a smart bolt.
A smart bolt allows you to not worry about the tension being used for torque and especially when lubrication and stainless steel are involved.
Is a stainless torque value different than a non-stainless torque value?
yes. Usually 2-3 lbs difference.
Can you use a lubricant with a stainless fastener and should you for torque value?
No. Because this can change the torque reading by as much as 40%
Single phase motor types are named how? NJATC, Motors 2nd edition, Single Phase motors, PP 160
Single phase motor types are named for the method used to develop the rotating magnetic field.
what do all motors have? NJATC, Motors 2nd edition, Single Phase motors, PP 160
All motors have a stator and a rotor.
A single phase motor and a 3 phase motor are nearly identical, except in what aspect? NJATC, Motors 2nd edition, Single Phase motors, PP 160
Single phase motors are different from 3 phase motors in that the windings in the single phase stator are placed 180 degrees apart, versus 120 degrees in three phase.
Both start and run windings (in the stator) in a single phase motor are in series or parallel? NJATC, Motors 2nd edition, Single Phase motors, PP 160
Parallel. So that the high resistance start winding can be disconnected by use of a centrifugal switch for instance.
The start winding in the stator on a single phase (2 pole) motor is placed how many mechanical degrees apart from the run winding and why? NJATC, Motors 2nd edition, Single Phase motors, PP 160
90 mechanical degrees apart to allow the motor to start in either direction.
Is the rotor in a single phase motor different from a 3 phase motor? How? NJATC, Motors 2nd edition; Single Phase motors, PP 160
No. Only the stator is different.
Explain the difference between the start and run windings on a single phase motor and how this facilitates starting. NJATC, Motors 2nd edition; Single Phase motors, PP 161
Run winding has many turns and heavy wire = high reactance
Start winding is smaller and has higher resistance
This creates a phase difference between the two windings.
When the rotor is locked in place, the lack of rotation is the result of what? NJATC, Motors 2nd edition; Single Phase motors, PP 162
The rotor becomes locked in place as a result of the stator and rotor fields being parallel to each other.
In a typical dual voltage motor, what is done with the run winding? NJATC, Motors 2nd edition; Single Phase motors, PP 163
The run winding is split into two sections.
Run windings are wired in what way for high and low voltage? NJATC, Motors 2nd edition; Single Phase motors, PP 162
Series is high voltage and parallel is low voltage.
Going to a series circuit in a single phase motor increases your voltage by two, and what happens to the impedence? NJATC, Motors 2nd edition; Single Phase motors, PP 162
As the voltage is doubled, impedence increases, and the current decreases, this means what for the cost of the installation?
Impedence increases by a factor of 4
An increase in voltage means less current and thus ampacity of conductors decreases, resulting in less cost in the installation.
To reverse the direction of most single phase motors, what is done? NJATC, Motors 2nd edition; Single Phase motors, PP 163
The two start leads are reversed.
What power source is required for a universal motor? Where are these motors used? NJATC, Motors 2nd edition; Single Phase motors, PP 163
Either AC or DC is used for universal motors and typically used in residential applications for high torque and speed. (Remember: residential is usually 1hp or less and single phase, fractional frame size motors)
A three phase motor is reversed using T1 and T3 leads as an industry standard for safety reasons, Leaving T2 permanently connected to L2 in case of Hi-leg. So A single phase motor reverses by switching the two start leads which are what? What color? NJATC, Motors 2nd edition; Single Phase motors
Single phase motors are reversed by switching T5 and T8 which are black and red.
A shaded pole is what? NJATC, Motors 2nd edition; Single Phase motors, PP 164
A short circuited winding.
Shaded pole motors are typically what HP or less and have low or high start torque? NJATC, Motors 2nd edition; Single Phase motors, PP 164
Shaded pole motors are typically 1/20 HP or less and have low starting torque. (In us markets motors rated less the 1/20 HP are rated in watts. -Motor name plates)
How many stator salient poles are in a shaded pole motor's stator? NJATC, Motors 2nd edition; Single Phase motors, PP 164
2 or more divided into parts.
The shaded pole is at its strongest when what? NJATC, Motors 2nd edition; Single Phase motors, PP 166
The shaded pole is at its strongest when the flux is at its maximum, at 90 degrees behind the maximum current in the main pole.
Reversing a shaded pole motor is different from reversing a standard single phase motor how? There is a second method requiring what? NJATC, Motors 2nd edition; Single Phase motors, PP 166
The rotor must be removed from the housing and turned around.
A second method requires de-energizing a shaded pole and energizing the second one.
Slip in the shaded pole motor is a problem? T or F? NJATC, Motors 2nd edition; Single Phase motors, PP 166
Slip in a shaded pole is not a problem, as the current in the stator is not controlled by a counter voltage determined by the rotor speed, as in other types of single phase motors.
Define a split-phase motor. NJATC, Motors 2nd edition; Single Phase motors, PP 167
A split-phase motor is a single phase AC mtor that includes a run winding and a resistive start winding that creates a phase shift for starting.
Split phase motors are used where? what are thier HP ratings? NJATC, Motors 2nd edition; Single Phase motors, PP 167
Where starting is easy. from 1/30HP - 1/20 HP.
A split-phase motor has a stator constructed with what? What is used to disconnect the run windings from the start windings? NJATC, Motors 2nd edition; Single Phase motors, PP 167
The stator in a split-phase motor is constructed with both start and run windings, using a centrifugal switch to diconnect the run from the start windings.
A centrifugal switch is defined as what? NJATC, Motors 2nd edition; Single Phase motors, PP 167?
A switch that disconnects the start winding when the rotor reacheds a certain preset speed.
The centrifugal switch opens and closes at what percent of full speed? NJATC, Motors 2nd edition; Single Phase motors, PP 168
The centrifugal switch opens at 75 percent of full speed and closes at 40 percent of full speed.
On a split phase motor the run and start windings have a usual phase difference of about how many degrees? What degree difference creates maximum starting torque? NJATC, Motors 2nd edition; Single Phase motors, PP 168
30 degrees is usual. Maximum starting torque would be at 90 degrees.
Reversing a split phase motor is done how? NJATC, Motors 2nd edition; Single Phase motors, PP 168
By reversing the start or run winding, but reversing the start winding is the industry standard.
A capacitor motor introduces capacitance into a single phase motor AC circuit to create what? NJATC, Motors 2nd edition; Single Phase motors, PP 168
To create a phase shift between the start and run windings.
What type of capacitors are used to start motors, and contructed how? NJATC, Motors 2nd edition; Single Phase motors, PP 169
AC electrolytic capacitors, contructed with two capacitors in opposite polarities.
What gives a capacitor start motor higher starting torque? NJATC, Motors 2nd edition; Single Phase motors, PP 170
Larger wire used in the start windings.
The capacitor start motor is also known as what? NJATC, Motors 2nd edition; Single Phase motors, PP 171
capacitor start induction run motor.
A capacitor-run motor has the start winding and capacitor connected in what way? NJATC, Motors 2nd edition; Single Phase motors, PP 171
In series at all times.
What is the advantage of leaving the capacitor in the circuit on a capacitor run motor? NJATC, Motors 2nd edition; Single Phase motors, PP 171
The motor has more running torque than a capacitor start or split phase motor.
How does the speed control of a capacitor run motor work? NJATC, Motors 2nd edition; Single Phase motors, PP 172
By adding impedence to the run windings and increasing slip.
A capacitor run motor has the start and run windings connected one at a time? T or F? NJATC, Motors 2nd edition; Single Phase motors, PP 172
False. Capacitor run motors have the run and start windings connected at all times.
To reverse a capacitor run motor, what must be done? What is different between the windings? NJATC, Motors 2nd edition; Single Phase motors, PP 173
To reverse a capacitor run motor the capacitor is switched from one winding to the other. The start and run windings are identical, except the start winding is the one with a capacitor connected to it.
A dual capacitor motor is a.k.a. ? NJATC, Motors 2nd edition; Single Phase motors, PP 173
start and run motor.
A capacitor start and run motor has two capacitors connected in__________ and both in _________ with the start winding. NJATC, Motors 2nd edition; Single Phase motors, PP 173
remember the start winding has a centrifugal switch.
A capacitor start and run motor has two capacitors connected in parallel and both in series with the start winding.
A capacitor start and run motor has a cetrifugal switch that does what? NJATC, Motors 2nd edition; Single Phase motors, PP 173
A capacitor start and run motor has a cetrifugal switch thatdesconnects the large capacitor that is in series with the start winding. The start winding is left in the circuit, creating more running torque than a capacitor start motor.
What is a bleed resistor used with and why? NJATC, Motors 2nd edition; Single Phase motors, PP 175
A bleed resistor is used with a start capacitor in rapid cycling because it does not fully discharge during start up, causing arcing without a bleed resistor. In electronics, a bleeder resistor is a resistor connected in parallel with the output of a high-voltage power supply circuit for the purpose of discharging the electric charge stored in the power supply's filter capacitors when the equipment is turned off, for safety reasons.
A bleed resistor is used at what ohmic values and wattage rating? NJATC, Motors 2nd edition; Single Phase motors, PP 175
A bleed resistor is used at an ohmic value between 12K and 20k and are usually rated at 2W.
Motor wiring methods inside a terminal box include what? NJATC, Motors 2nd edition; Single Phase motors, PP 177
direct wire, terminal post, and terminal post with links.
The most common terminal box wiring method is what? NJATC, Motors 2nd edition; Single Phase motors, PP 175
The terminal post method is the most common terminal box wiring method. Below is the terminal post with links. Remove the links and now you have just terminal post.
The ends of a motor winding lead that require periodic changing have what type of lugs? NJATC, Motors 2nd edition; Single Phase motors, PP 177
spade.
Terminal post with links is a wiring method inside a terminal box for a motor and are used as what? NJATC, Motors 2nd edition; Single Phase motors, PP 175
Terminal post with links are used as jumpers to change motor direction.
in a dual voltage single phase motor the start and run windings are typically what color and number. NJATC, Motors 2nd edition; Single Phase motors, PP 174
Red and Black start windings (red) T5 and (black) T8 and the run windings are (blue) T1 and (yellow) T4.
In a single voltage single phase motor application, what are the run windings and start windings? NJATC, Motors 2nd edition, Single Phase motors, PP 174
In a single voltage single phase application the run windings are T1 and T4 and start windings are T5 and T8
The 4 sates of matter are what? Name the fourth.
1. Solid
2. Liquids
3. gases
D) plasmas
Matter can form other matter.
False
Matter can only combine with other matter to form compounds
The basic structural components of the universe are?
B) matter
Energy and matter are associated with each other.
True
the first law of thermodynamics is the law of ______________?
A) conservation of energy
Absolute zero is what temperature?
0 kelvin or -273 centigrade
The reason the efficiency of any process will always be less than 100% is?
As disorder increases in the universe (entropy) energy transforms into less usable forms.
The first of law of thermodynamics states what?
This is what allows us to determine the efficiency of a system
The total amount of energy in the universe is constant.
If all movement of matter stops at -273C or 0 kelvin then this means what cannot occur at this temperature?
C) The transfer of energy cannot occur.
mind blown
The two types of energy are what?
kinein to move GREEK kinētikos
Kinetic and Potential
Chemical energy is found where
This is stored in the bonds of atoms and molecules
This is a form of energy that travels in transverse waves
The oscillation of the electrical field of the wave moves perpendicular to the direction the wave is travelling, making it a transverse wave.
electromagnetic energy
This is formed when and electric field couples with a magnetic field.
Electromagnetic waves
This is also called the end light spectrum. This includes gamma rays, x-rays, ultraviolet, visible light, infrared, microwave, and radio wave.
Courtesy Bureau Veritas
electromagnetic spectrum.
This has longer cycles compared to ultraviolet and visible light. It has a lower frequency.
Recall that when they discovered the universe was expanding they realized this because they saw colors of red in the light. Thus the wavelengths are very long
Infrared light or radiation.
Light absorption, reflection, and emission spectra is a physical property of an object?
False
The human eye responds to wavelengths of light at what length?
380-750 nanometers
The frequency of light is a trillion times faster than the frequency at your electrical outlet.
True
430THz Tara hertz
The term used to measure the number of cycles per a unit of time is what?
named after Heinrich Rudolf Hertz (1857–1894), the first person to provide conclusive proof of the existence of electromagnetic waves.
frequency. Expressed in Hertz
When radiant energy is absorbed by an object, that object simultaneously emits the same amount of energy that was absorbed.
True
This is similar to the ground heating up in the sunlight.
absorbs and emits
D) In general, the higher the temperature, and the more opaque and reflective, the more infrared radiation it _________.
Consider carbon used in Graphene that absorbs all light and is 300 times stronger than steel. It is considered a superb conductor.
Disorder in the universe causes energy to change into more usable forms
False
less usable forms. Consider that order; for example a bridge, is actually chaos to the natural world. Thus steel bridging is a less usable form of energy.
The basis of all thermal testing is based on what 4 criteria represented by the acronym TEAR
4. Transmission
1. Emission
2. Absorption
3. Reflection
Is low wavelength thermal energy able to pass through glass or most other materials?
Germanium is used for the lenses on infrared thermal cameras.
TRUE
The effects of transmissivity for most materials is insignificant when compared to reflectivity, but still must be factored when determining a material's absorptive and emissive properties.
blackbody radiation is the energy emitted by materials that absorb energy similar to a black body.
True
blackbody radiation, energy radiated by any object or system that absorbs all incident radiation. The term usually refers to the spectrum of light emitted by any heated object; common examples include the heating element of a toaster and the filament of a light bulb.
Infrared passes through glass.
consider a green house and why it gets hotter
False
The glass heats up and then radiates heat to its surroundings that allows them to radiate.
To ensure that there is a full pixel on the target there must be ___ array of pixels for temperature reading.
D) 3x3
Which of the following are elements we must understand to create a good thermal image?
D) dynamic range and all of the rest
individual temperatures in an infrared image are displayed as colors and shades of a?
D) palette
Emissivity is considered a ratio. What is the ratio of a black body?
The lower the emissivity the harder it is to predict the exact temperature of an object.
A black body has an emissivity of 0%. The emissivity is the percent of total energy radiated at a given surface at a temperature given/to the total energy radiated by a blackbody at the same temperature.
A thermal surface with an emissivity of 0 would have no thermal emittance and appears black.
A perfect thermal mirror has an emissivity of 0.
False
radiated/ blackbody radiated means 0 is 0 energy radiated thus all energy is reflected and a black body at 1 would be a perfect emitter
What during thermal scanning in commissioning can provide a perfect reflection and lead to a false temperature reading?
Anything shiny. Specifically anthing with an emissivity of 0 since it is a Perfect Thermal Mirror.
Two concepts used to understand the relationship between an objects infrared radiation level and its surface temperature.
C) Planck's Blackbody Distribution Law & Wien's Law of Displacement
The radiation of a perfectly emitting blackbody intensifies as it's temperature does. Wiens law illustrates that infrared is a longer wavelength than what you can see with the naked eye but you may see it if it becomes intense enough.
Wien's Displacement Law is stated how? Select the BEST answer.
If the materials emissivity is known, Wien's Law allows us to use wavelengths, or frequencies, to determine the surface temperature.
A) That the temeprature of an object increases, the peak INTENSITY moves to shorter wavelengths.
The light in the visible spectrum is shorter and as infrared radiation intensifies it becomes shorter in wavelenth.
The purpose of Wien's Law?
As the temperature of an object increases, the peak intensity moves to shorter wavelengths
What law allows us to calculate the surface temperature in infrared?
Planck's Blackbody Distribution Law states that the intensity of radiation emitted from an object is a function of it's temperature, wavelength, and emissivity.
True
Shiny surfaces have high emissivity and high reflectivity
False
The emissivity of a shiny surface is low. Think of emit as the root word. It reflects highly. Thus it cannot absorb and emit infrared radiation well.
Infrared cameras display the temperature based on?
B) emissivity
infrared sensor temperature x emissivity = actual temperature
the relative power of a surface to emit heat by radiation
the more reflective the surface, the lower the absorptivity and emissivity of the material.
D) emissivity
a measure of the ability of a surface to radiate energy; the ratio of the radiant flux emitted per unit area to that emitted by a black body at the same temperature
tape emissivity x metal temperature ÷ tape temperature is used to find a metal's emissivity
True
You can accurately measure emissivity for objects at the same temperature as the background.
False
If the object and background temperature are equal, the camera will see the same result no matter the emissivity.
When a reflective object is emitting energy to the IR camera, it emits according to its emissivity and its temperature.
False
An opaque object is emitting energy to the IR camera, it emits according to its emissivity and its temperature. Reflective objects have a low emissivity because emissivity is a ratio. a measure of the ability of a surface to radiate energy; the ratio of the radiant flux emitted per unit area to that emitted by a black body at the same temperature
For opaque objects, reflectivity is complementary to emissivity and is equal to one, minus the objects emissivity.
True
when it reflects energy to the IR camera, it does so according to its reflectivity and
D) the temperature in the background.
the temperature in the background is necessarily in variation or nothing would be identified or seen.
The emissivity of black electrical tape is what?
B) .97
emissivity is a ratio of the radiation reflected / that reflected by a black body. at the same temperature.
Tape emissivityx metal temperature ÷ tape temperature= metal emissivity
True
Keep in mind that this method is less accurate if the metal is too close to room temperature. As metal tends to reflect the ambient temperature around it.
Using the determining material types equation (Tape emissivity x metal temperature ÷ tape temperature = metal emissivity) what must you keep in mind that would make the method less accurate?
If the metal is too close to room temperature, as metal tends to reflect the ambient temperature around it.
Perfect black bodies are materials that emit energy and have an emissivity of?
D) 1
emissivity is a ratio of the radiation emitted/ black body radiation at the same temperature. A black body is an idealized object that absorbs all electromagnetic radiation it comes in contact with. It then emits thermal radiation in a continuous spectrum according to its temperature.
A black body emits all electromagnetic energy?
False
A black body is an idealized object that absorbs all electromagnetic radiation it comes in contact with. It then emits thermal radiation in a continuous spectrum according to its temperature.
A black body absorbs thermal radiation in a continuous spectrum according to its temperature.
False
A black body is an idealized object that absorbs all electromagnetic radiation it comes in contact with. It then emits thermal radiation in a continuous spectrum according to its temperature.
When performing an IR scan, the target is assumed to be a grey body rather than a black body. Why?
Grey bodies have an emissivity less than one that is constant through wavelengths. Black bodies emit all thermal energy (but absorbs all electromagnetic energy)
If an IR camera measures an object with a temperature of Absolute Zero, the reading would come back Absolute Zero, regardless of what?
B) of what the emissivity of that object is
The temperature is absolute zero which means no exchange of energy can occur.
The degree to which infrared energy is absorbed by a material.
A) absorption
all materials are continuously and simultaneously conducting and absorbing infrared energy is a true statement. The best answer is however given.
If absorption is the degree of infrared energy absorbed by a material and absorptivity is the proportion of radiant energy that is absorbed into the material, then what would a real world material reflect if it is a black body that perfectly absorbs. Considering thermal radiation.
A real world black body cannot be a perfect black body as it will always reflect a small part of the incident radiation, resulting in absorptivity that is always less than one.
What is the difference between absorption and absorptivity?
absorptivity is the opposite phenomenon to emissivity which is the proportion of infrared energy radiating from a surface, and infrared energy is instead absorbed by the material
If absorption is the degree to which infrared energy is absorbed & absorptivity is the proportion of radiant energy that is absorbed.
Remember: the more reflective the surface, the lower the absorptivityand emissivity of the material.
reflectivity is what?
D) ratio of the intensity of the total energy reflected from the surface to the radiation on that surface.
The degree to which infrared energy reflects off a material is reflection and not reflectivity.
To accurately calculate the emissivity of an object what must be added?
the ratio of the amount of electromagnetic flux reflected by a surface to the total amount of electromagnetic flux incident on the surface is defined by this term.
D) ratio of reflectivity must be added to the total in order to accurately calculate this.
The ratio of reflectivity is the ratio of the amount of electromagnetic flux reflected by a surface to the total amount of electromagnetic flux incident on the surface.
The degree to which thermal energy passes through a material.
A) transmission
Kirchoff's law states that?
D) the ratio of radiation intensities for two surfaces is equal to the ratio of their absorptivity
Gustav Robert Kirchoff came up with many laws.
Good reflectors are good emitters.
False
Kirchoff's radiation law explains why good reflectors are always bad emitters, and vice versa.
convection versus conduction. What is the difference?
The movement of particles through a substance, transporting their heat energy from hotter areas to cooler areas is convection. Conduction however, doesn't necessarily involve particles moving. Instead energy is passed from one particle to another upon contact from a solid surface, transferring heat.
This is the fastest method of heat transfer., heat is transferred by electromagnetic waves traveling at the speed of light.
D) radiation
The total energy of an object is expressed using one of two formulas with only one difference between them. What is it? Regarding Kirchhoff's law regarding the ratio of radiation.
transmissivity is (physics) a measure of the capacity of a material to transmit radiation
absorptivity & emissivity are the only difference in total energy of an object with both regarding transmissivity
absorptivity + reflectivity + transmissivity = total energy
emissivity + reflectivity + transmissivity = total energy
range is the temperature difference than an infrared camera can measure?
True
What does the first and second law of thermodynamics state?
in the thermography test it will ask if the total amount of energy in the universe is constant. Answer true even though this is in violation of the law as this would not be a closed system
1. First Law of Thermodynamics states that total energy in a closed system is neither lost nor gained — it is only transformed.
2.The Second Law of Thermodynamics states that entropy constantly increases in a closed system.
What is the difference between transient heat flow and steady state flow?
In transient heat transfers, the heat energy transferred through the medium is not constant. The heat flow rate keeps changing, and the cause of the varying rates of heat transfer can be either fluctuating temperature differences over the medium or changes in properties of the medium.
Steady-state conduction occurs when the temperature at all locations in a substance is constant with time. Thermal conductivity is an important property of matter. It accounts for the heat conducting ability of a substance and depends both on the particular substance involved and on the state of that substance
The transfer of heat through a moving medium such as a liquid or gas.
A) convection
passive devices emit signals and radiation and ignore what the target emits?
False
Passive thermography does not require any active illumination (such as lights) or specialized equipment, making it extremely useful for inspections in dark or enclosed spaces. Active thermography is the use of emitters to illuminate objects with infrared light and then take images using an infrared camera.
What causes the temperature of a given point to change over time?
B) transient heat flow
During a change of the state of matter, the supplied energy is not used to increase the kinetic energy of the molecules, but to change the binding energies. Therefore, the temperature remains constant.
Heat transfer comprises convection & conduction but not radiation as this is energy and not heat.
True
radiation is a form of energy transfer as all exchanges of temperature difference are forms of energy.
The basis of quantitative analysis is always comparing dissimilar equipment under similar loads?
pay close attention to the words being used.
False
qualitative (not quantitative) similar equipment under similar loads.
A direct reading measures the surface temperature of the target without other insulating materials affecting the results.
motors, steam traps, and tank levels are all forms of indirect readings
True
This is always the easiest way to perform a quantitative analysis. indirect uses insulation and is very difficult.
This form of analysis is done using a baseline inspection performed with subsequent inspections to build a thermal map to determine if any changes have occurred over time.
C) qualitative evaluation
this is a comparison.
As the temperature increases the thermal resistance decreases?
False
As the temperature decreases, thermal resistance increases. Think conductivity.
The larger the surface, the greater the loss of thermal resistance as the temperature decreases.
True
The loss of thermal resistance is more because the area is larger and resistance always decreases as directly proportional to temperature and thus area as well.
It is sometimes necessary to heat a cold room in order to locate this with thermal imaging.
C) trapped moisture
It makes sense because cold air would transition slower than the air around it to the new temperature.
Thermal Anomalies can be grouped into which categories?
there are 5 forms of thermal anomalies: think not as seen.
The difference between endothermic and exothermic reactions is endothermic reactions draw heat in from their surroundings and exothermic reactions give heat off to their surroundings.
True
For field quantification it is required that proper device calibration requires that the thermographer factors the emissivity of the object into the calibration.
True
a lower emissivity setting is used for highly reflected objects and a high emissivity setting is used for low reflective objects. Where emissivity is the amount of radiation emitted by an object compared to the amount emitted by a perfect emitter at the same temperature.
During FIELD QUANTIFICATION where a baseline temperature is used for determining operating temperature limits, correctly adjusting the emissivity settings is unimportant when taking measurements because correct settings will appear hotter or colder than what they really are due to baseline measurements.
False
adjusting the emissivity settings is important when taking measurements because INCORRECT settings will appear hotter or colder than what they really are
We can determine emissivity through the following procedure.
1. apply a known emissivity coating to the unknown object.
2. heat the object and emissivity coating to 60F above the background temp.
3. set the camera emissivity to .95, target the black vinyl tape. record its temp.
4. target a part of the heated object next to the tape and lower the camera's emissivity setting until the temperature displayed matches the temperature previously recorded for the tape.
The key to a successful measurement is to have a measurement location where the background temperature is significantly less that the object temperature.
Shiny objects have high emissivity?
False
Emissivity is defined as the ratio of the energy radiated from a material's surface to that radiated from a perfect emitter, known as a blackbody, at the same temperature and wavelength and under the same viewing conditions. It is a dimensionless number between 0 (for a perfect reflector) and 1 (for a perfect emitter). Thus shiny would be the opposite of a black body at 1 and give incorrect readings for temperature as high.
IF A THERMAL imager set for a high emissivity is used to measure an object with lose emissivity, the following occurs. :
In an object that has low emissivity and is shiny, the measured object is warmer than ambient temperature, the reading will be much higher than the object's actual temperature.
high emissivity with a low emissivity object will skew the results.
False
IF THE MEASURED OBJECT IS WARMER THAN AMBIENT: the reading will be much LOWER than the object's actual temperature.
IF A THERMAL imager set for a high emissivity is used to measure an object with lose emissivity, the following occurs:
In an object that has low emissivity and is shiny, the measured object is COLDER than ambient temperature, the reading will be much HIGHER than the object's actual temperature.
high emissivity with a low emissivity object will skew the results.
True
IF A THERMAL imager set for a high emissivity is used to measure an object with lose emissivity, the following occurs. IF THE MEASURED OBJECT IS COLDER THAN AMBIENT: the reading will be much HIGHER than the object's actual temperature.
Polished metals like stainless steel have a very high emissivity. This occurs because the metal is primarily reflecting the thermal radiation from its surroundings.
in emissivity a perfect reflector is 0 and a blackbody is 1. Because ratio of the energy radiated from a material's surface to that radiated from a perfect emitter, known as a blackbody that always would be 1 if perfect.
False
polished or shiny means a low emissivity because it would be 0 for a perfect reflector.
If we heat stainless steel to 150F and look at it with the infrared camera set for the same emissivity of .95, the camera will report a surface temperature how?
A) much lower than the objects temperature. because the surrounding emissivity.
adjusting the emissivity value on the thermal imager until the reading matches 150 will provide an emissivity of .12 Remember a perfect reflector is 0.
Thermal anomalies are visible to the human eye?
False
We call them anomalies because what we see is our primary sense and thus nomalous or normal.
Most thermal imaging inspections for predictive maintenance use a quantitative approach.
False
Most thermal imaging inspections for predictive maintenance use a qualitative approach that is more concerned with differences between similar components under similar loads than with precise, quantitative temperature measurement.
What is the difference between quantitative and qaulitative?
Quantitative data is numbers-based, countable, or measurable. Qualitative data is interpretation-based, descriptive, and relating to language
Most thermal imaging inspections for predictive maintenance use a quantitative approach.
True
Most thermal imaging inspections for predictive maintenance use a qualitative approach that is more concerned with differences between similar components under similar loads than with precise, quantitative temperature measurement.
what in a set of prints contains detailed information about what size and type of materials are to be used on a job? (NC set: general)
schedules
What is a list of detailed job requirements under which all work must be performed? (NC set: general)
specifications: usually printed on 81/2 x 11 paper and bound
What is the difference between addendums, revisions, and change orders? (NC set: general)
An addaddendum occurs before bid (addendum is adding)
Revisions dated changes in prints or specs with a cloud around it
change orders occur after bids are opened and MUST BE SIGNED in order to ensure payment
What must be done daily and eventually turned in to the contractor before payment is made? (NC set: general)
Working drawings or as-builts
All horizontal and vertical measurements begin from this point? (NC set: general)
point of beginning: could be a stake or pin buried in the ground
What schedule provides mounting and routing info for electrical devices and is used primarily on commercial or industrial prints? (NC set: general)
room schedules
What schedule lists and identifies circuit branches? (NC set: general)
panel schedules
In a residential application the lighting schedule may be replaced by a ________ ______ that the owner will use to select their lighting at a local store? (NC set: general)
lighting allowance
Floor plans usually are represented by a cutting plane at ____ feet height with objects below the line represented by a solid line and above represented by a hidden line. (NC set: general)
5
cabinets are in sizes __ inches wide and ___ increments thereafter. (NC set: general)
9 and 3
____ plan will tell you about exterior lighting and relationships to exterior buildings. A.K.A. sight plan. It will also tell you where to locate the service. (NC set: general)
Plot plan
___ _______ diagram shows you where panels go and how they are connected. (NC set: general)
One line
What scale is based on 1/2 inch and 1/4 inch? (NC set: general)
Mechanical engineer’s scale
Where do you find information about circuit breakers? (NC set: general)
The panel schedule
If there is no information on what height to place a switch then you do what? (NC set: general)
Use standard practice- 48 inches.
Who had the authority to make changes? (NC set: general)
The architect
The maximum irradiance at any point on the Earth is what? Measured with what? (NC set: general)
1000 watts/ meter squared
pyrometer
What is the smallest of the standard architectural print sizes? (NC set: general)
A
North azimuth for a compass is what degree? (NC set: general)
00 or 3600
0 degrees for a solar calculation is what? (NC set: general)
South, and working counter clockwise. East is 90, west is 270
The panel is greater than 10 feet from the inverter, what must be used? (NC set: general)
A disconnect
The standard used to investigate snap switches would be? (NC set: general)
Ul20
The white book assists with NEC _______. (NC set: general)
Enforcement
Width of a working space must be _____ or the width of the panel, whichever is greater. (NC set: general)
30 inches
The door of an electrical panel has to be able to open how far? (NC set: general)
90 degrees
Headroom is what height? What is dedicated space? (NC set: general)
6.5 feet / 6 feet above equipment
The parts of a 3 way switch are? (NC set: general)
______traveler
Shunt ___
______traveler
When a switch opens it is rated on its _______. (NC set: general)
Voltage
When it closes, a switch is rated for ________. (NC set: general)
Current
An illegal 3-way switch (California 3-way) controls a load by doing what? (NC set: general)
Switching between the hot and neutral
Switches in multiple always start and end with what? Meaning how many 4 ways can be used in travelers of a circuit? DC theory PP 79 (NC set: general)
3-ways
As many 4 ways as we want
The number or circuit paths we can control are called ________ and the number of positions we can close are called _________. DC theory 79 (NC set: general)
Poles and throws.
A wire .001 inches in dia. is considered ________ or _______ in diameter. (NC set: general)
1cm or 1mil inch
What is the formula for calculating cross sectional area of a conductor in cm (circular mils)? (NC set: general)
(dia. in inches x 1000) square the result
Internationally the conductor size is expressed in what? Using what formula? (NC set: general)
Square millimeter (mm2) Using Area= p R squared (where p=3.14159 R=radius
Calculating cross sectional dia. in mm squared is different from circular mils how? (NC set: general)
Using radius in mm versus dia. in inches.
I.E.C. standards for K are metric values of? (NC set: general)
The resistance of a conductor 1m long and 1mm in diameter
What is the formula for resistance in a conductor? (NC set: general)
R=(KxL) divided by A (R-resistance, K-specific resistance, L- length, A-circular mil inch squared)
To calculate CM for a rectangle use what formula? (NC set: general)
[(LxW) x 1000] /.7854 = square mils
The basic formula for voltage drop is ___________. (NC set: general)
the VD formula for single phase & not DC or 3 phase
VD= 2KLI/Cm
Mnemonic: Venereal disease = 2 Kalashnikovs divided by communists
Watt loss is also known as what? What is the formula? (NC set: general)
Line loss or heat loss. Formula is P=I^2 x R
Different watt lamps have the same ________ rating. How? (NC set: general)
Voltage. Because resistance and current are inversely proportional (change in opposite directions) while voltage will not change in the circuit.
What is the formula for watts used in each component versus the entire circuit? (NC set: general)
P= I^2xR / P=It x R1
Identify the difference between a rheostat and potentiometer. (NC set: general)
Potentiometer- voltage three leads connected across the load
rheostat- current two leads, from the greek rheo meaning stream
The formula for law of proportionality is what? Used in _______ for voltage and _______ for current. (NC set: general)
It (rt/rn) mnemonic: rt = r top
In parallel for current and series for voltage.
Values that change in the same direction are ________ proportional and values that change in opposite directions are __________ proportional. (NC set: general)
Directly / inversely
A motor starting will draw typically ____ current as when it is running. (NC set: general)
6 x as much
A pump draws more/ less current when the inlet is plugged or closed. (NC set: general)
Less
The 0 (green) and I (red) symbol on an on/off switch is the European version of what? (NC set: general)
Off and on. Mnemonic: off= zero current and on= 1 or some current
There are 2 types of al to cu connections. What are they? (NC set: general)
UL listed AL/ CU adapter or gutter splice
There are 2 types of connectors used with aluminum conductors. (NC set: general)
Mechanical screw type and compression type.
AL AWG and CU AWG is what? (NC set: general)
The same
A solder less lug is what? (NC set: general)
A chair lug
Conductors larger than #8 AWG are what? (NC set: general)
Stranded (test instrument pp. 24)
Ampacity is based on what type of current? (NC set: general)
Continuous
More than three current carrying conductors must be ___________. (NC set: general)
Derated
A switch leg is the wire going __________ . (NC set: general)
Directly to the device
The law of magnetic poles states that ________ poles attract and ________ poles repel. (NC set: general)
Unlike
Like
The approximation method for resistance in a length of conductor is what? (NC set: general)
Drop the last digit from circular mils (cm) and this equals the number of feet for approximately 1 ohm resistance.
The rigid Thread cap color codes are?
Blue is whole inch size, black is 1/2 size, and Red is 1/4 sizes. Conduit bending PP 5 (NC set: general)
Chapters 2, 3 & 4 in the NEC are referred to as the _____________ chapters. (NC set: general)
Plan, build, use.
The square footage of a building is measured by the ___________ of a building. When converting from feet and inches to square feet the trick is to convert to _________ form. (NC set: general)
Outside
Decimal
NEC 220.12
When converting to yards of concrete from a dimension in feet and inches squared divide by ________. (NC set: general)
27
If a circuit is a continuous load, how much can you load the circuit? (NC set: general)
80%
NEC
Installations that comply with the NEC are considered adequate for service and future expansion. True? (NC set: general)
False.
NEC 90.1(C)
What chapters of the NEC apply generally? (NC set: general)
1-4
NEC 90.3
Receptacles rated ____ amps or less and designed for the direct connection of aluminum conductors shall be marked co/alu (NC set: general)
20 amps NEC 406.2(C)
Where installed in raceways, conductors _______ awg and larger shall be stranded. (NC set: general)
8 AWG and larger
NEC 310.3
The NEC requires at least one outlet in every room be ______ for lighting. (NC set: general)
Switched
NEC
The phase arrangement on 3- phase buses shall be ________ from front to back and top to bottom. The ___ phase shall be that phase having the higher voltage to ground on 3-phase, 4-wire delta-connected systems. Other bus bar arrangements shall be permitted for additions to existing installations and shall be marked. (NC set: general)
A,B,C,
B
NEC 408.3(E) Switchboards and panel boards
For other than a totally enclosed switchboard, a space not less than _____ shall be provided between the top of the switchboard and any combustible ceiling, unless a noncombustible shield is provided between the switchboard and the ceiling. (NC set: general)
3 feet
NEC 408.18 (a)
The conduit or raceways, including their end fittings, shall not rise more than ______ above the bottom of the enclosure. (NC set: general)
3 inches
NEC 408.5
All panel boards shall have a rating not less than the _______ _______ ______required for the load calculated in accordance with parts II, III, IV, or V of article 220 as applicable. (NC set: general)
Minimum feeder capacity
NEC 408.30
A cabinet can be installed up to ___ inches deep in non-combustible walls and _____ with combustible walls. (NC set: general)
1/4 inches
flush
NEC 312.3
Conductors ______AWG or larger shall be installed with a round insulation ring. (NC set: general)
4
NEC 300.4(G)
The NEC recommends that voltage drop on branch circuits not exceed 3% at the farthest outlet of power, heating, and lighting loads, and where the maximum total voltage drop on both feeders and branch circuits to the farthest outlet does not exceed _______. NEC 210.19 (A) 1 FPN 4 (NC set: general)
5%
If a circuit changes amplitude over time, but not polarity it is called what? (NC set: general)
A DC circuit. (A.C. theory WB PP 14)
Two sine waves of the same frequency are said to be in phase when they both cross the __________at the _________ going in _________ . A.C. theory WB PP 14 (NC set: general)
Reference line
Same time
Same direction
A D.C. generator has _____, and an A.C. generator has______? (NC set: general)
commutator
slip-rings
When ________lines of flux are cut in __________, _______ is produced. (NC set: general)
1 million
1 second
1 volt
The formula for the time required for one cycle is what? (NC set: general)
T=1/F
The ________ is the real wave form typically available at an outlet. (NC set: general)
Peak to Peak (A.C. theory pp. 33)
There are ___ measurements of voltage and current associated with a sine wave, they are: _____. Their formulas are? (NC set: general)
4 measurements of voltage and current with a sine wave:
Peak 1.414 (RMS / EFF)
Effective or RMS .707 (peak)
Average .637 (peak)
Peak to Peak 2x (1.414x RMS)
Note: Effective alternating-current voltage or effective ac current is the equivalent value of direct-current voltage or dc current that will produce the same amount of heat in a resistor.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, Based on the 2014 NEC PP 68
What value will always be larger than the RMS value? (NC set: general)
Peak.
The value not used in true AC but rather when AC is converted to DC using a full wave rectifier is? (NC set: general)
Average (A.C. theory pp.35)
The actual Average is the ________ voltages or current values across a full cycle; therefore a true A.C. sine wave has an average value of _______.
Instantaneous (A.C. theory pp. 35)
Zero
RMS is also known as _____ and has the same heating effect of D.C. at that value. (NC set: general)
Effective is also known as this.
Note: Effective alternating-current voltage or effective ac current is the equivalent value of direct-current voltage or dc current that will produce the same amount of heat in a resistor.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, Based on the 2014 NEC PP 68
One important thing to remember is that in an AC circuit when a voltage value is given it is always the ________ or ________value. A.C. WB PP 40 (NC set: general)
One exception to this is the Peak to Peak value available at an outlet or receptacle.
Effective or RMS
Note: Effective alternating-current voltage or effective ac current is the equivalent value of direct-current voltage or dc current that will produce the same amount of heat in a resistor.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, Based on the 2014 NEC PP 68
The formula for instantaneous voltage or current values in a sine wave is? A.C. PP 32 (NC set: general)
V instantaneous = peak (sin(theta))
The theoretical purely inductive circuit consumes _______ power. Why? A.C. Theory WB PP 64 (NC set: general)
No. Because energy is stored in the magnetic field created by the current flow through the coil
Power used by the resistance of the circuit is called the _________of the circuit and is measured in watts. A.C. theory WB PP 65 (NC set: general)
True Power
When current and voltage are multiplied it is called the __________. AC theory WB PP 65 (NC set: general)
Apparent power
The Ratio of the True Power to the Apparent Power is called the _________ of the circuit. AC theory WB PP 65 (NC set: general)
Power Factor
Power Factor can range from 0 to 100 and is usually reported as a percent. The ratio is equal to the _______. A.C. theory WB PP 65 (NC set: general)
Cosine of?
Cosine theta
Also true is R/Z, TP/AP. (Where R is resistance, and Z is impedance. TP is true power and AP is apparent power)
A power Factor can either be _________ or ________. In which cases? A.C. theory WB PP 65 (NC set: general)
Eli the Ice Man
Leading or lagging
Inductive: Current lags voltage ELI Voltage leads current
Capacitive: Current leads voltage ICE Current leads voltage
In a purely resistive A.C. circuit, current and voltage are ________. A.C. WB PP 40 (NC set: general)
In phase with one another
Inductive Reactance Xl, or CEMF (counter electromagnetic force) is 1800 out of phase with the applied voltage and causes the ________ to lag behind the applied line_____ by________. A.C. theory pp. 58 (NC set: general)
Current
Voltage
900
Each acute angle of a right triangle has _______ ratios associated with it. Each ratio is formed by using the lengths of _____ sides of the triangle. These six trigonometric ratios are? Math pp. 438 (NC set: general)
6
2
sine, cosine, tangent, cosecant, secant, and cotangent
A physical quantity described by a single number is called a ________ quantity. math pp.472 (NC set: general)
Scalar
A physical quantity that has both a magnitude and a direction is called a _________. math pp. 472 (NC set: general)
Vector
A vector written in component form is positive and negative when? math pp. 474 (NC set: general)
Positive when to the right or upwards
Negative when left or downwards
To get the component (coordinates) form of a vector do what? math pp. 475 (NC set: general)
Subtract the initial point from the terminal point: Ix-Tx and Iy-Ty
When a vector is in standard position, the x and y components are the coordinates of the vector's______. math pp. 475 (NC set: general)
Terminal point
If we know the component form of a vector we can find the _________ of a vector by Pythagorean Theorem, and the _________ of the vector by trigonometry. The angle theta can be found using what? math pp. 487 (NC set: general)
Magnitude
Direction
Tan(theta) = vy/Vx
The horizontal component of a vector can be found using _________ and the vertical component can be found using _________. math PP 495 (NC set: general)
Cosine of theta = x
Sine of theta = y
The equation that expresses frequency is? A.C. WB 14 (NC set: general)
F= 1/T
To calculate the times constant for a circuit have L and R values, you use the formula_______. AC WB PP 43 (NC set: general)
T= L/R where t= one time constant
One time constant is equal to _______ of maximum value. A.C. WB PP 44 (NC set: general)
63.2%
Maximum current (I max) is equal to_________. A.C. WB PP 31 (NC set: general)
I max is a value associated with batteries
Battery voltage rated
Battery internal resistance
Whenever a conductor cuts through magnetic lines of flux, a(n) _________ is induced into the conductor. A.C. WB PP 41 (NC set: general)
Voltage
What is meant by the term time constant in an inductive AC circuit? AC WB PP 43 (NC set: general)
Ratio between inductance and resistance
RNC is prohibited form use where it is subjected to ambient temperatures in excess of ________ F. conduit bending PP 8 (NC set: general)
If the length change in a run of PVC exceeds ______ due to thermal expansion, an expansion fitting must be provided. conduit bending PP 7 (NC set: general)
122 F
1/4" Usually in a length of approximately 100 feet of conduit in an approximate 6 degree F change. See NEC table 352.44
The NEC says that there shall not be more than how many 90's (quarter bends) between pull points such as conduit bodies or boxes? conduit bending PP 4 (NC set: general)
4. However 3 in fire alarm circuits
The Equipment Grounding Conductor provides a path to the service ground in case of what? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1)
Ground fault.
Low impedance ground means what? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1)
Low opposition to current.
The correct term for opposition to current in an ac system is? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 11
Impedance.
What is the name given to the opposition to current offered by the internal structure of the conductive material? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 12
Resistance.
Grounding of a system or metal objects is referred to as __________? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 12
Earthing.
Current takes all paths or the path of least resistance? IAEI, Soares Book on Grounding and Bonding(notecard set g&b1), PP 12
All paths.
What path must be available for current to exist? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP13
A complete path
The grounding safety circuit must meet 3 criteria. What are they? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 14
1.Continuous path
2.Adequate capacity for fault
3.Be of low impedance
What term defines: the more current through an ocpd the quicker it acts. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 14
Inverse Time
The grounding of the grounded conductor of a system is accomplished how? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 15
by a connection to ground through a grounding electrode conductor either at the service or at a separately derived system.
The grounded conductor is used only on what side of the service grounding connection? Why? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 15
Line. Because connection on the load side creates multiple paths for grounded current and can energize equipment and conduits
The difference between the term main bonding jumper and system bonding jumper is what? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 15
Because of the word and in the definition, what would be the main bonding jumper in a main panel? IAEI, Soares Book on Grounding and Bonding (notecard set g&b1)
The main bonding jumper connects the grounded service conductor to the equipment grounding conductor and the service enclosure, whereas the system bonding jumper does the same at separately derived services.
A hook shaped piece of metal bonding the can to the grounding bar, identified by a green screw.
Desensitizing the GFP device occurs when what happens? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 18
Multiple paths for current are available.
A conductive path from the point of a ground fault though the normally non-current carrying part of an electrical system to the electrical supply source is best described as a?
A. Ground-fault current path
B. Ground Fault
C. Grounded, Solidly
D. Effective Ground-Fault Current Path
ANSWER: A. Ground Fault current path. Note: an effective ground fault current path would be low-impedence.
What is the difference between the term effective ground-fault current path and ground fault current path? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 19
Effective means intentional and path means electrically conductive. A ground fault is unintentional.
Isolated versus guarded means what? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 20
Isolated means not readily accessible; whereas guarded is.
What is permitted to be used as a substitute for grounding? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 20
Double insulation
Anything grounded is? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1)
forced to take the same potential as Earth
Where the ungrounded system conductors are installed in grounded metal raceways or enclosures, the ungrounded system becomes? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 23
Capacitively coupled to ground
The severity of electric shock is related to four elements? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1)
1.amount of current
2.duration of exposure
3.path
4.frequency
Three types of electrical burns exist. They are ____________? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 24
Electrical
Arc
Thermal contact
Where the electrical system is not grounded, the electrical equipment is? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1)
Connected to earth at the service and bonded
Dairy cattle are so sensitive to electricity that a potential of as little as _______ volts between conductive portions of floors, walls, piping and stanchions caused behavior problems that resulted in lost production. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 25
2 volts
The phrase likely to become energized is included in Annex B of the NEC Style Manual as a standard term meaning _______________. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 1 & 27
Insulation failure can result in two kinds of faults. What are they? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 28
Failure of insulation on
Line to line or line to ground
The measurement of insulation resistance is usually what form of electricity and between how many volts on under 600 volt systems with what? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1)
DC, 500 to a 1000, and with a meger
A high voltage dielectric test is often called? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 29
Hi-pot test
A grounded system conductor, such as a neutral conductor, that is not generally considered to be grounded again past the service disconnecting means can be considered what? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 30
Ground fault
A conductor's long time rating can be thought of as ampacity where its short time rating can be thought of as its __________ rating. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 32
Withstanding
Where a delta-connected high voltage system is used to supply portable or mobile equipment, a system neutral shall be derived. This is usually accomplished by means of a(an)? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 40
Zigzag grounding transformer
AC systems over ________ volts are permitted but not required to be grounded. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 40
1000
Examples of separately derived systems include? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1)
Generator systems with no neutral connection to the utility
Transformers with no primary to secondary connection
Rectified power
Inverters and batteries for uninterruptible power systems
PV
A High impedance grounded system has all the advantages and non of the disadvantages of an ___________ and is used where facility operation cannot be halted. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1)
ungrounded system
Examples of systems that are not separately derived include. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 41
Autotransformers
Generators not connected to a transfer switch, which switches all conductors at once
Typical ungrounded systems always use what type of transformer? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1)
Delta
When an ungrounded system with one ground fault experiences a second ground fault on a different phase, the result is a _____________ on the system. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 43
Phase to phase fault
In 600 volt systems, the two greatest source of capacitance to ground are? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 45
Conductors in metal conduit and windings
Capacitance to ground is known as? Versus current from conductors to ground? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1)
Leakage capacitance versus leakage current or charging current.
Disadvantages of an ungrounded system are? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1)
Power system over voltages
Transient over voltages
System voltages above ground are not necessarily balanced or controlled
Destructive arcing
Not all grounded conductors of a system are? What is one example? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 54
Are all nuetrals grounded conductors?
Neutrals
For example, a ground phase conductor of a three-phase, three-wire, delta connected system is a grounded phase conductor, not a neutral of the system
Yes
Grounded conductor identification for MI cable is located where? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 55
At its terminations
The following grounded systems are usually grounded in what manner? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 57
Low voltage (under 600v)
Medium voltage (2.4-15KV)
High voltage systems (34.5KV and up)
IAEI,
Low voltage: almost always solidly or high impedance grounded.
Medium voltage: either solidly or resistance (low or high resistance PP 361) grounded.
High voltage: grounded through surge arresters or ungrounded
Where three transformers that have center taps are connected in a delta bank, How many transformer(s) may have thier midpoint grounded? Why? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 57
One
Since there is a difference in potential between the midpoints of each transformer and will create a short.
High leg voltage to ground (b phase) equals what? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1)
total of phase (A and C only) to N times 1.732 = B high leg pp.58
Where an ac system operating at less than 1000 volts is grounded at any point, the grounded conductor shall be run to what? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 67
Each service disconnecting means
Table 250.66 and T250.122 generally refer to what? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 71
Remember the grounded conductors is based on the largest kcmil phase conductor and this question is not asking that
T250.66 - grounding electrode conductor based on service conductors added kcmil
T250.122 - EGC equipment grounding conductor based on OCPD sizing
The minimum size of the grounded service conductor that must be run to the service disconnecting means is based on what? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 71
Based on the size of the ungrounded service entrance conductors, and not on the service circuit breakers or fuses.
The formula for the five second withstand rating of a bare copper conductor is? WB 54 / IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 209
The bare five second withstand rating must be used in what case only? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1)
cm divided by 29.1
Used only where the equipment grounding conductor does not come into contact with the insulated current carrying conductors!
The basic rule for all enclosures that contain a service conductor is what? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 85
That they must be bonded together.
The formula for the five second withstand rating of an insulated copper conductor is? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1)
These values are proportional to the values given where? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1)
cm divided 42.25
Table 250.122 in the NEC
What NEC table provides conductor applications and insulations? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1)
T310.16b
To get low impedance of the grounding system in an ac system what must be done? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 194
The circuit conductors and the equipment grounding conductor must generally be kept together at all times.
Not grounding the metallic enclosure can lead to what? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 195
Large induced voltages in surrounding metallic structures.
The difference between the grounded and ungrounded system is what? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 196
The ungrounded system only has an equipment and enclosure grounding system and no grounded conductor.
Circuit breakers have a different trip curve depending on whether they are_____? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 198
Single, double, or three-pole configurations.
The method employed for clearing a short circuit is different depending on whether the circuit is grounded or not. T or F? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1)
False. Remember a grounding (EGC) conductor is for clearing ground faults.
The term current limiting indicates that a fuse will start to melt and clear the circuit in how many electrical degrees? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 199
Melt in 90 and clear in 180 (half cycle)
Whether fault current is a short circuit or a ground fault, the over current devices behind the device will see all of the fault current? T or F? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 200
False. The ocpd ahead of the fault will see all of the current.
When clearing a ground fault, two things control the current? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 201
The impedance of the circuit, and the available short circuit current of the system.
Emergency systems over current protective devices are required to be what? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 201 NEC 700.27
Required
Selectively coordinated with all supply side over current devices.
The grounded service conductor will carry how much of the fault current in most cases. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 203
90% or more.
If conduit couplings are installed wrench tight, as required by code, the increase in impedance of the conduit with couplings is about ________ % more than a straight run without couplings. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 206
50%
Table 250.122 has a rule of thumb that the equipment grounding conductor should not be less than ________% of the capacity of the phase conductors or the amp rating of the over current device that supplies the circuit. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 208
25%
The I2T values of the conductors given in Table 250.122 are about how many times their nominal continuous rating based on how many amperes for every __________ cm cross section. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 212
13 and 28
one
42.25 (Bare 5 second withstand rating)
When 3-phase systems are installed, the primary is usually what type of connection? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 216
What does a delta connection mean about which conductors are installed? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1)
Delta connected: secondary may be delta or wye
A nuetral conductor is not installed
A separately derived system has ___________ electrical connection? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1)
No direct
What must be provided to the service or source of supply from the primary side of a transformer? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) WB 58
An equipment grounding conductor
Conductors derived from the secondary of a transformer, generator or other separately derived systems are considered what and are often referred to as? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 221
Unprotected or unfused (line side) conductors and are often referred to as tap conductors.
The sizing of the system bonding jumper for a separately derived system is to be based on? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) WB 59
Derived phase conductors supplied by the separately derived system.
A separately derived system that is grounded must have a grounding electrode conductor(s) to provide reference to earth for the enclosures and grounded conductor? T or F? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 222
T
Metal water piping must be used as a grounding electrode for a separately derived system within _________feet of entering the building. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 224
5
In a separately derived system, the grounding electrode shall be... IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1)
The grounding electrode shall be the nearest one of the following: NEC 250.30(a)7
as near as practicable to and preferably in the same area as the grounding electrode conductor connection to the system.
Metal water pipe
Structural metal grounding electrode
The grounding electrode conductor taps in a separately derived system must be connected to the common grounding electrode conductor where? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 225
At an accessible location.
Pertaining to Liquidtight flexible metal conduit used as an equipment grounding conductor, the maximum ampere ocpd protecting contained conductors for 1/2 and 3/8th and for 3/4 through 1-1/4 sizes is? The maximum ground return path cannot exceed what length? NEC 250.118 IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 158
Liquidtight cannot be used as an equipment grounding conductor under what circumstance? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1)
20 amps - 1/2 and 3/8th
60 amps - 3/4 through 1 1/4
6 ft
Where flexibility is necessary after installation.
The maximum amperes allowed on an ocpd to protect the conductors contained in flexible metal conduit when it is used as an equipment grounding conductor is? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1)
Under what condition can flexible metal conduit not be used as an equipment grounding conductor? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 158
20 amps
where flexibility after installation is required.
A person can become a path in an electrical circuit in one of two ways. What are they? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 250
Series and parallel contact
Series contact and Parallel contact are different in what ways? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 250
Series = the person is the only path to ground and no equipment grounding conductor involved
Parallel = equipment grounding conductor involved
The GFCI continuously monitors the current balance between what two conductors? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 251
Hot and neutral
Several kitchen appliances, as well as portable heaters, are manufactured with 2-wire supply cords and, therefore, do/do not have their housings or enclosures grounded. Personnel can be protected by use of a ________. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 251
Do not
GFCI
The most common two types of GFCI's are? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 252
Circuit breaker and receptacle types
GFCIs shall/ shall not be required for receptacles installed in those critical care areas where the toilet and basin are installed within the patient room. NEC 517.21
Shall not
The definition for bathroom uses what term that defines it not as a room? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 259
Area.... not room.
GFPE is required for what systems? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 267
Solidlygrounded wye electrical services of more than 150 volts to ground but not exceeding 600 volts phase to phase for each service disconnect rated 1000 amps or more.
The maximum setting for GFPE shall be how many amperes? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 268
1200
GFPE: A system intended to provide protection of equipment from damaging line to ground fault currents by operating to cause a disconnecting means to _________________. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 269
Open all ungrounded conductors
There are two types of GFPE systems. What are they? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 269
Zero-sequence (residual) and ground strap type
The neutral ground strap type has a unique design feature in that what passes through the current sensor? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 269
Main bonding jumper
GFPE provides protection from burn downs at less than or greater than the ocpd rating? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 274
Less than.
The major advantage and disadvantage of a neutral ground strap type GFPE is(are) what? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 269
The advantage of a neutral ground strap type is that it is the least expensive, and the disadvantage is it is limited to application at the main service or supply source.
The zero sequence (residual) and ground strap type of equipment ground fault protection system consists of a___________. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 269
current sensor, control relay, and usually a shunt trip circuit breaker or shunt trip fused disconnect switch
The most popular type of GFPE is? Also known as what and why? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 271
Zero sequencing type
the ground fault relay or system vectorally sums up the current through all four sensors and considers any excess current as residual.
The ground fault relays that receive the input from the zero sequencing EGFP are field adjustable with what pickup ranges? Typical ranges for service are? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 272
4 to 1200 amperes
100 to 1200 amperes
Note: shunt trip relays are usually connected through a shunt trip breaker or switch.
GFP time delay settings are available in what range? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 272
1.5 cycles to 60 cycles or one second
The two most common types of selective coordination schemes are? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 273
Cascading time delay scheme and the zone interlocking system.
The hazardous locations in 501.30, 502.30, and 503.30 are primarily comprised of what respectively? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) Wb81
Dust, gas, and ignitable fibers or filings.
Hazardous locations generally require a(an) ________________in the raceway. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 282
Equipment grounding conductor
Hazardous locations generally require that locknuts on each side of the enclosure, or a locknut on the outside and a bushing on the inside can/ cannot be used for bonding. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 282
Cannot
Typical voltage ratings of conductors are? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 192
300, 600, 2000, 5000, and 15000
The main bonding jumper is permitted to consist of a(an)? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 81
Wire, green screw, bus or other similar suitable conductor.
What must carry the full ground-fault current of the system back to the grounded service conductor? its size must relate to what? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 84
Main bonding jumper
the rating of the service conductors.
What defines a ground ring. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) Wb 25
A copper conductor not smaller than 2awg and at least 20 feet long that encircles the building or structure and is buried at least 30 inches deep
A concrete encased electrode (ufor ground) is not less than?
Not less than 2 inches in depth and 1/2 inch in diameter or 20 feet or more of bare copper conductors not smaller than 4awg. Wb 25
Under what condition can an underground water pipe be used as a grounding electrode? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) WB 24
A metal underground water pipe that is in direct contact with the earth for more than 10 feet shall be permitted to be used as a grounding electrode.
Underground metal gas piping and aluminum can be used as grounding electrodes? True or False?
False
Where used outside, aluminum or copper clad aluminum grounding conductors shall not be terminated within ____ " of the earth. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) Wb 25
18"
Where plate electrodes are used, they shall have at least ______ square feet of surface in contact with exterior soil. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 26
2
Rod and pipe electrodes require how many feet in contact with the soil? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1)
8
If a ground rod cannot be run vertically, or at a 45, then it can be run horizontally but must be how far under the soil? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1)
30"
Where must supplemental grounding electrodes be used? (NEC 250.56) IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1)
Where a single rod, pipe, or plate electrode that is being used as a grounding electrode does not achieve a resistance to ground of 25 ohms or less, at least one additional electrode must be used.
The grounding electrode conductor is permitted to be not larger than AWG CU/ AWG AL where it is the sole connection to a rod, pipe, or plate electrode. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) WB 30 (NEC 250.66a)
6 CU
4 AL
Isolated powers systems are grounded/ ungrounded systems? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 298
Ungrounded
Isolated power systems usually consist of what? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 299
usually consists of a transformer that has an ungrounded secondary.
The primary purpose of an isolated power system is to allow the equipment to do what? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 299
To function with the first line to ground fault without opening an OCPD.
What must never be used on isolated power systems. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 299
Wire pulling compound, since it has an adverse effect on the dielectric characteristics of the conductors and the system operation.
Section 680.25(B) requires that, pertaining to pools, the equipment grounding conductor from a separately derived system be sized in accordance with what? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 303
T250.66 based on the size of the derived phase conductors.
(note that this is the grounding electrode conductor sizing table, and not the equipment grounding conductor sizing table)
Why is bonding required in a pool? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 304
To reduce voltage gradients in the pool area.
The mean of equalizing the potential of all equipment and parts so there will be no current between parts is referred to as? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 304
Equipotential bonding.
When an interconnection between the grounded (neutral) conductor and bonding grid exists this interconnection is often condidered what in regards to pools? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 304
remote from the pool and is not intended to play a part in equipotential bonding.
UPS systems are covered in section 645.15 of the NEC for IT rooms and specifically states that they shall not be considered what type of electrical system? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 325
Separately derived
The NEC does (does not) define what objectionable current is? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 325
Does not
Currents that introduce noise or data errors in electronic equipment shall (shall not be) considered the objectionable currents. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 325
Shall not be
The earth shall never be used for what purpose? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 326
As an effective ground fault current path
The electrical supply source is what? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 326
utility transformer (or)
seperately derived system
The equipment grounding conuctor and the isolated equipment grounding conductor use what two phrases in IT jargon? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 326
Safety ground and clean ground
Should an equipment grounding connection ever be made to a local grounding electrode when dealing with IT? why? A local grounding electrode is what? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 326
Never, becuase the grounding path resistance is too high.
A local grounding electrode is building steel, water pipe, or driven electrodes.
Does the NEC address whether isolated grounding is required, and this is addressed by whom? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 327
No. The owner, design engineer, or manufacturer usually address this
Isolated grounding means what? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 327
The enclosure supplied by the conductors in the raceway will be isolated by use of one or more nonmetallic raceway fittings.
The term ground loops is (is not) defined in the NEC? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 329
Is not
What causes a ground loop? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 329
Connecting computers and terminals on different circuits that are grounded to building steel (will allow) the shielded communications cable between the computer and terminal to complete the ground loop.
what will cause noise current and can couple with data signals?
Many computers data signals operate at how many volts? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 329
Difference in ground potential
5 volts or less
A device to interface between an unbalanced transmission line (a single signal referenced to ground) and a balanced transmission line (two driven signals referenced to each other). Quite often both signals are referenced to ground but they need not be. Balanced signals used on computer communication systems are often two opposing signals each fluctuating between 0 and +5 volts or some other voltage. What is used to isolate noise.
Isolating baluns can and are used at the end of long balanced transmission lines (such as twisted pairs) to eliminate noise because noise picked up along the line affects both signals at the same amplitude and phase.
A Balun coil is what? Is it effective at all frequencies?
where does the term balun come from?
A coil of insulated wire on a non-metallic core.
no
Baluns. A Balun is used to "balance" unbalanced systems - i.e. those where power flows from an unbalanced line to a balanced line (hence, balun derives from balance to unbalanced). ... An unbalanced transmission line (coaxial cable) connected to a dipole antenna.
What are some interface devices? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP329
Surge arrestors and surge protective devices (SPDs)
Known solutions to the problem of ground loops include? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 329
Single point grounding
Balun coil
Modems
Fiber optics
Optical insulators
Interface devices: such as surge arresters and surge protective devices (SPDs)
Single point grounding is not suitable when? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 329
At high frequencies and when in long distances using shielded cables
The signal reference grid serves as a signal reference plane over a broad range of frequencies. They are correctly referred to as what? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 331
Broad band grounding systems
The signal reference grid is an effort to reduce, eliminate or control the tendency of conductors connected to computers to resonate at lower frequencies. True or False? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 331
False: they resonate at higher frequencies
The effectiveness of the broad band grounding system or signal reference grid is improved how? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 332
if it is solidly connected to the power supply for the it equipment by a very short strap
Resonance occurs when? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 333
the length of a conductor and the frequency of the alternating current are in tune.
Good engineering practice requires that a conductor any longer than 1/20 of a wavelength cannot be counted upon to equalize voltages between its ends. This amounts to only 4.4 ft at 10 MHz. The significance of this is that unless conductors can be limited to less than ______ft in length, conventional grounding techniques with single point grounds might not be effective for signal and noise frequencies up to 10 MHz. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 333
4-5 feet
The use of what two methods appears to be the simplest and most reliable method for dealing with signals over 10MHz in frequency? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 333
Multi-point grounding
Short conductors
Single-point grounding is typically applied to analog circuits with signal frequencies up to what? While digital circuits with signal frequencies in the what range should utilize multipoint grounding? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 334
300 KHz
MHz
Surge arrestors are permitted to be only installed at the service. True or False? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 334
False: they may be at the service or on the load side of the service
Two types of surge arresters become conductive when what is exceeded? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 334
Threshold voltage
Grounding systems create a path for what?
Ground faults
Surge protective devices come in 4 types. What are they? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 336
Type 1: secondary of service transformer to line side of service disconnect
Type 2: Load side of service disconnect (at branch panel)
Type 3: point of utilization
Type 4: Component SPD's
Define a non-linear load. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 336
A load where the wave shape of the steady-state current does not follow the wave shape of the applied voltage.
A nonlinear load can cause several problems in the electrical supply system. Name 2. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1)
Overloading neutral conductors
Creating excessive heat in transformers.
Harmonic currents appear as reflected waves are multiples of the fundamental root frequency sine wave (60hz). The 3rd, 5th, and 7th are what freq? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 336
3rd = 180hz
5th = 300hz
7th = 420hz
Engineers will often specify what type of transformer in IT installations. They are designed for what? Rating is what? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 336
K transformers designed to handle the excessive heat from harmonics in the windings. K4-K20
The term grounding conductor is referring to what? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 337
The conductor that is connected to an electrode that functions similar to a grounding electrode conductor.
Most medium voltage systems in the ______ to ________kv range are either low resistance grounded or high resistance grounded. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 361
2.4-15kv
It is common in industrial systems to ground the neutral of systems rated ________volts and above through a resistor. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 361
2400
Reactance grounding (use of a reactor or grounding transformer) in the 2400 volts range is preferred if the circuits are overhead. Why? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 361
Due to lightning
Systems rated 15000 volts or more are usually ________ grounded, which permits the use of grounded neutral type ___________ that cost less and provide better protection from over voltages. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 361-362
Solidly
Surge arrestors
Copper bus is rated on __________amperes per square inch. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 362
1200
A system neutral point is used for grounding high voltage ungrounded systems. The grounding type transformers include which kind? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 363
Zigzag, wye-delta, T-connected (also known as Scott T)
Solidly grounded neutral systems have two types of grounding. What are they? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 363
What must be done with systems under 1kv? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1)
Single point and multi-point
Multipoint and must be a grounding electrode every 1300 feet.
The neutral conductor of a solidly grounded systems is generally permitted to have an insulation level of not less than ________volts or to be bare. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 363
600 volts
Single point grounded neutral systems are permitted for systems ________volts and greater. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 363
The National Electrical Code (NEC™ Article 230.95(B)) requires ground fault protection (GFP) for equipment installed on solidly grounded 277/480 volt electric services rated 1000 amps or more.
1000
Impedance grounded neutral systems can be accomplished by what 3 methods? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 364
Reactance grounding
Low resistance grounding
High resistance grounding
Lightning protection systems consist of what 4 parts? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 372
Strike termination network
Down conductor network
Grounding electrode network
Equipotential bonding network
Strike termination devices include what? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 375
Air terminals
Metal masts
Building steel at least 3/16 inch thick
The lightning zone of protection is determined by two methods. What are they? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 375
Protective angle
Rolling sphere (most popular)
Air terminals are required to be located within _______of the ridge ends on pitched roofs or at edges and outside corners of flat or gently sloping roofs. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 376
2 feet
The zone of protection for an air terminal device is how many feet if not near flammable gases, etc.? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 375
150
Each strike termination device must be provided with a minimum of ________ path(s) to ground and additional down conductors are required on structures exceeding ________ ft in perimeter. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 379
2
250
Down conductors are usually near corners of buildings. Why? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 379
Corners provide a higher probability of streamer development and therefore lightning strike attachment.
Approved lightning protection ground rods shall extend vertically not less than ________feet into the earth. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 381
10
Where corrosion is an issue, the bond between the incoming piping system and the lightning protection grounding system may be made through a _________. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 383
Spark gap
Magnetic and capacitive coupling from a lightning strike occurring up to __________ feet can induce a transient capable of damaging electrical and electronic systems. IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 384
1500 feet
An underground gas line can be used as a grounding electrode? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 386
No
Under art 250 there are two types of current paths. What are they? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1)
Effective ground fault current path and ground fault current path
Where do you connect the neutral conductors on a PDU? What is this point called? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 325
On the line side nuetral point of the service only, before the disconnect.
Where are the connections to the signal reference grid in an IT room made? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 332
Various IT units are connected by a flat copper braid and to the power supply for the IT units by a very short strap.
Where does a system of less than 50 volts ac require grounding? NEC 250.20A IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1)
Where transformer supply exceeds 150 volts to ground
Where the transformer supply is ungrounded
Where installed outside as overhead conductors
Equipment grounding conductors provide what?
An effective ground fault current path to facilitate OCPD operation in ground fault conditions.
IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 155
The term primary and secondary systems refers to what voltage respectively? IAEI, Soares Book on Grounding and Bonding, (notecard set g&b1) PP 36
Primary systems = 600 volts or more
Secondary systems = 600 volts or less
The unmoving part of a 3 phase motor, consisting of a core and windings, or coil is called what?ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 74
stator.
An alternator provides what type of current? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 71
AC.
Which is cheaper? Three phase or single phase motors? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, WB PP 17
Why?
3 phase.
Low maintenance requirements and economy of operation.
Define synchronous speed. ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 79
& what it is based upon.
The speed of the field as it rotates around the stator and is based on the frequency and the number of poles.
The formula to calculate synchronous speed is what? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 79
Synchronous speed = (120 x F)/P
P= number of poles
F= frequency
There are how many stator windings for each pole in a 3 phase motor? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 76
3
In a 3 phase motor, there are 3 sine waves placed how far apart? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 79
Is electrical degrees and mechanical degrees relatively the same thing? pp 79
120 degrees.
Not at all.
Define rotor frequency. ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 80
The rate at which the stator magnetic field passes the poles in the rotor.
Do the rotor conductors have high resistance or reactance? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 80
Low resistance but high reactance due to the high frequency.
At synchronous speed the rotor continues to induce a current on the stator. T or F? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 80
False. There is no longer any relative motion at synchronous speed. The stator current is controlled by CEMF determined by the rotor speed, therefore no slip.
What is E coil for a Delta and a Wye configured motor? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 81
E coil (Delta) = E line
E coil (Wye) = .58 x E line
What represents the true power and working force of a motor? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors
The HP available at the end of the shaft or FLC.
What must be done to reverse a 3 phase motor? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, WB 18
What is the industry standard? Why?
interchange any two of the 3 phase power lines to the motor.
Interchange T1 and T3 only. Due to Hi legs, and allows T2 to be permanently connected to L2 to insulate T1 and T3 from each other.
A motor operating at 60 HZ operates at what speed compared to one operating at 50 HZ? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 90
20 percent faster.
What is the difference between torque and work force? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 91
consider force and an axis when answering
Torque is in lbs per ft and work is in ft lbs.
Torque = length x force. Explanation: The torque is the force of one pound being turned on an axis with a radius of one foot; therefore, one pound per foot. A similar mistake is made with generators, as they produce DC, not AC...by definition.
The three types of loads are what? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 93
constant horsepower, constant-torque, and variale-torque loads.
Multispeed 3 phase motors are designed to operate at what number of speeds? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 93
2, 3, or 4.
During startup, when is maximum torque achieved? What happens to current and voltage? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 92
When the rotor fequency decreases to the point at which the winding reactance is equal to its resistance. At this point, the current in the rotor lags exactly 45 electrical degrees behind the voltage.
What happens in regards to Horsepower in a constant torque load motor? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 93
HP changes proportionally to the speed.
____________ is also refered to as breakaway torque or starting torque. ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, WB 18
Pull-up torque.
When can true power only be produced? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 95
When current and voltage are both positive or both negative.
Power Factor is sometimes called what? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 96
Displacement Power Factor.
What is the Formula for Power Factor? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 96
The Horse Power version
A low power factor indicates what about a motor? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 96
That the motor is drawing more current than required by the load.
The power factor can be improved how? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 96
The power factor can be improved by adding capacitors in parallel with the inductance.
A power factor correction capacitor should meet what requirements? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 96
It should have the same amount of reactance as the inductor to canel out the reactive power of the unductor.
Motor efficiency is calculated how? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 96
By dividing the output power by the input power.
The five major components of motor energy losses are what? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 96
The five major components of motor energy losses are
1 resistance: stator and rotor
2 bearing: friction loss
3 core: hysterisis and eddy currents
4 windage: cooling blades
5 sound: it takes energy to make noise
Resistance losses are found in what components of a motor? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 97
Resistance losses in a motor are found in the stator and the rotor.
Two types of diagrams used with motor cuircuits are? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 99
Ladder and wiring.
What type of drawing does not show the location of components in a motor circuit? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 99
Ladder diagram versus wiring diagram.
What can be used to measure the voltage and current unbalance? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 100
A 3 phase power quality meter.
Can a motor be rewired in the field from delta to wye or wye to delta? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 101 (summary)
NO!
Define eddy current. ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 98
This type of current is an undesired current circulating in the stator and rotor core caused by magnetic induction.
Define hysterisis. ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 98
This is a loss due to the power consumed to realign the magnetic domains in the iron twice every electrical cycle.
Define flux linkage loss. ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 98
This is the loss of flux in the air gap because he air gap has increased reluctance compared to the cores.
Power factor correction capacitors can be placed where on an electric motor drive in the AC supply lines? Not where? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 96
These can be placed ahead of an electric motor drive in the AC supply lines but not between the drive and motor.
The four most common types of torque related to motors are what? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 91
Locked rotor torque, full-load torque, pull-up torque, and breakdown torque.
At start up when a motor is in locked rotor, what are the only limits to current flow? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 80
Windage resistance and reactants are the only limits to current flow at this point in a three-phase motor.
At start up when a motor is in lock rotor, what are the only limits to current flow? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 80
In a three-phase motor windage resistance and reactance are the only limits to current flow at this point.
In a three-phase motor as a load is placed on the rotor, what happens? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 80
The rotor slows and the frequency increases in a three-phase motor when this happens. Producing a stronger pole to provide the necessary torque to carry the load.
Describe the operating principle that causes three-phase motor rotation. ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 79
Electrical energy creates a field in the stater windings that rotates around the frame. These revolving field poles cut the conductors in the rotor, creating unlike poles that interact with each other to cause this.
Defined a salient pole or projecting pole. ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 78
This is a pole that extends away from the core toward the stator or extends away from the stator toward the rotor.
In a three-phase motor, there are three stator windings for each pole. The windings are placed in groups of three with each group connected in series or parallel for each phase? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 76
These are grouped and placed in series for each phase in a three-phase motor.
The stator in a three-phase motor consists of what? What does the rotor consist of? ATP & NJATC, Motors 2nd edition, Chapter 4: Three phase motors, PP 74
These both consist of a core and windings in each, respectively, in a three-phase motor.
A motor thermal device is either of the__________ or the ____________.
Bi-metal type or the melting alloy (solder pot) design. pp. 7 Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
The bi-metal type, as the name implies, has two (BI) dissimilar metals laminated together. As the two metals are of different types, the expansion rates are different when heat is applied. This difference in expansion rates causes the laminated piece to bend or warp. This warping action_____________.
Opens a set of normally closed contacts. PP7Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
The overload section of the starter, as the name implies, protects the motor from overloads and/or?
Phase failure. PP6 Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
The contactor opens and closes contacts using the electromagnet principle, is restricted to?
Fixed lighting loads, electric furnaces and other resistive loads that have set current values, or portions of a motor control circuit that do not require OVERLOAD protection. PP6 Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
Overload devices are of three basic types:
Thermal, magnetic, and solid state. PP6 Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
Heaters have letter and/or number designations which are used for proper sizing. Each manufacturer uses?
Different designations, so there is no industry standard. The manufacturer’s data must be referred to for the being used. PP8 Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
Bi-metal overload device is adjustable, much like a thermostat. The standard adjustment range is from 85% (closer) to 115% (farther away? The adjustment is often used to increase the overload setting to eliminate?
Nuisance tripping. PP8
The second type of thermal overload device is the melting alloy type, commonly called the solder pot type. This device basically consists of?
A ratchet wheel with a shaft that sets in a tube; : tube is filled with a metal
(a metal with a low melting point) After the metal has cooled, the device can be manually reset. pushing the reset button is like cocking a gun. PP9 Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
In regards to the solder pot overload. Installed in the Low position the heater coil is lower on the tube and…? A.The eutectic metal will melt with _____ current, and higher up in position it will melt with _____ current. PP9
less …. more.
To eliminate the need for gigantic sized heater elements and associated overload relays, current transformers are used (pis. 129) current transformers are standard on what size starters?
NEMA size 5 and larger starters. Motor Controls- Richard Cox, 2nd edition. PP11
60HP for 240 volt and 125HP for 480 volt motors start at NEMA size 5.
To compensate for starters that are located in high operating temperature locations, _________must be installed conversely, in low temperature areas, ________ elements are installed. PP10
Oversized heaters …undersized heaters.
Some bi-metal units are designed to compensate for changes in ambient temperature, This type is labeled as?
Compensated overload relay. PP10
On the Window or Donut-type CT’s, the conductor, bus bar, or bushing which passes
through the center of the transformer constitutes one primary turn. On Window-type units with low primary current ratings, where the primary conductor size is small, the ratio of the transformer can be changed by taking multiple wraps of the primary conductor through the window. If, for example,
a window CT has a ratio of 100:5, placing two primary conductor wraps (two primary turns)through the window will
change the ratio to ______. Some types of equipment employ this method to calibrate the equipment or to permit a single ratio CT to be utilized for several different ampacities of
equipment.
50:5 ratio, or halfing the primary ratio is accomplished with each additional wrap of conductor through these.
The output of standard CT’s are usually, but not always, _____ max.
5 amp maximum output for these. Electricians Guide to AC Motor Controls- Richard Cox 1981 edition. PP11
Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
The most common CT secondary full-load current is 5 amps which matches the standard 5 amp full-scale current rating of switchboard indicating devices, power metering equipment, and protective relays. CT’s with a 1 amp full-load value and matching instruments with a 1 amp full-range value are also available. Many new protective relays are programmable for either value.
Caution: The secondary of a Current Transformer must always have a burden (load) connected; an open-circuited secondary can result in the development of a dangerously high secondary voltage. Energized but
unused CT’s must be kept________.
The secondary of these must always be kept short circuited to avoid a buildup of high voltage.
All current transformers are ________ polarity. Polarity refers to the instantaneous direction of the primary cur-
rent with respect to the secondary current and is determined by the way the transformer leads are brought out of
the case. On subtractive polarity transformers the H1 primary lead and the X1 secondary lead will be on the same
side of the transformer (the left side when facing the low-side bushings).
All of these have subtractive polarity, meaning they are polarity sensitive.
The secondary of a CT has one terminal marked for polarity, as indicated by? And this is what polarity?
The black dot represents the negative terminal on the secondary of this device. PP11 Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
When CT’s are used in conjunction with thermal overload relays they should be grounded on the?
secondary represented by a black dot on a CT with thermal overload relays. PP11 Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
Regarding the bushing CT, care must be taken with the installation to insure that the mounting clamp bolts do not contact what and why?
Also because the case is metal and is installed
externally it can decrease the_______. The circuit breaker or transformer manufacturer should be consulted to verify acceptability of the installation.
Care for these types of CT’s must be taken for contact to the metal case with the mounting clamp bolts resulting in a one-turn primary short circuit.
The bushing strike distance can be reduced due to the metal outside case of these type of CT’s.
Magnetic types of overload relays are of two basic types?
time limiting (Inverse time) and instantaneous trip. PP12 Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
Inverse Time: done with a purposely delayed action that decreases as the operating force increases —used especially of electrical relays: Mariam Webster Dictionary (OR)Inverse time tripping is a characteristic of circuit breakers in which the breaker trips in more time with lower overcurrent, and less time with higher overcurrent. source:http://www.schneider-electric.us/en/faqs/FA115818/
Time limiting or delay type (Dash pot) of magnetic overload, as shown, has a heavy gauge wire-wound wired directly in series with the motor leads or by use of what for larger motors, usually NEMA size 5 or larger? PP12 Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
CT’s to monitor motor current are used for these two types of overloads.
In a time limiting or delay type magnetic overload, the trip current level can be made by screwing the core of the relay? These are also called what type of relay or overload? Describe its operation.PP12 Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
Up or down, and is also called a Dashpot Relay. As the current increases, the pressure in the oil around the core will pass through small orifices and open the contacts.
instantaneous trip magnetic relay is not designed for normal overload use, as the primary use of this device is to? PP13 Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
Trip instantaneously at a preset current level.
Solid state overload relays are sealed electronic devices with three current sensing loops through which the ________ pass? PP13Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
motor circuit conductors…
Solid state overload relays are adjustable from? You can do what to provide for lower ranges? PP13
80 to 120% of the units rated value. By using multiple turns through the sensing loop (one for ea. phase), for instance, two turns in a 10 amp relay can provide protection for a 20 amp motor.
Solid state overload relays are virtually unaffected by? PP 13 Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
in what adverse type of environments do motors operate
ambient temperatures
Due to the large size and weight involved in closing the contacts of size 6 and larger starters, DC coils are used by most manufacturers to provide faster, more positive closure. ________ is used to produce the DC voltage necessary for the coil. DC eliminates the _____ that is associated with most larger sized starters and contactors. PP13 Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
A bridge rectifier and eliminates hum.
Arc quenching is also called?
Arc rupturing. PP13 Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
Two methods of arc quenching are? PP13 & 14
The arc to rises in the arc box or chute where it contacts de-ionization grids or plates and a series of small arcs, cooled and is rapidly extinguished. Another method used to quickly extinguish the arc caused by opening contacts under load is the blowout coil. Blowout coils are coils of wire connected in series with the contacts and the motor leads. Current flow through the coil sets up a magnetic field across the pole pieces as shown.
No matter what method is used for arc-quenching, the arc chutes or boxes also prevent the arcs from crossing phase to phase or phase to ground. For this reason, the starter or contactor must never be……? PP17 Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
…operated if the arc chutes are not in place If the chutes moved for cleaning or replacement, tag or lockout the starter to prevent it from being energized.
Normally in AC magnetic equipment, black wires are used in _______ and red wires are used for _______. bold lines denote the power circuit, and thin lines used to show the control circuit. PP18
power circuits & control circuits.
To energize the coil, it is necessary that what two potentials be available at the coil? PP 19. Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
Both L1 & L2.
Three wire control, as the name implies, will require three wires to control the motor circuit.
The third wire will allow use of momentary pushbuttons, float switches, limit switches, pressure switches, etc. Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
(Sp) Single pole, indicates? ST (Single Throw) indicates?
(Single Pole) indicates one circuit conductor can be opened or closed. Single throw indicates possible positions of the switch other than OFF. PP 30
silver or silver alloy reduces contact maintenance because?
the film caused by the arc when the contacts are opened and closed is silver oxide, which is itself a good conductor. PP31 Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
There are basically two types of contact ratings?
POWER and CONTROL- The power rated contacts are to carry and to interrupt large amounts of electrical current, whereas control contacts are smaller in physical size and are designed to carry only small amounts of electrical current (normally 10 amp continuous rating). PP31
A 115 volt single phase motor can be controlled by opening and closing the hot (Ll) conductor. The exception would be?
A 115V single phase motor used for a gasoline pump National Electric Code requires that all conductors be disconnected from the source of supply. A double pole switch then would be needed, one pole for each conductor LI and L2. PP32
SPDT is sometimes called a _________, because it can direct or transfer power to either of two loads. It will not, however, operate both loads at the same time (Fig- 3.7). PP33. Electricians Guide to AC Motor Controls; 1981, Richard Cox. Motor controls
transfer switch
To reverse the direction of rotation of a single phase (split phase) motor requires that the leads of the start winding be reversed • reversing the direction of rotation of a standard 3 phase induction motor can be accomplished changing or reversing any two line or motor leads. This can also be accomplished by a DPDT switch, or a four way, by switching what two leads?
L1 and L2.
Primary ocp can be responsive to secondary short circuits but is not always responsive to secondary overcurrent caused by? PP294
an unbalanced condition
Transformer "charging current" for smaller transformers is what compared to the ampere rating of the transformer? PP298
Proportionally larger for the ampere rating of the transformer. the va is always larger than the IxE rating, therefore rising and collapsing AC field in VARs is and therefore VA rating is always larger. The field suffers power loss due to hysteresis. Where the magnetic domains rise and fall two times in a cycle.
The overcurrent device protecting the primary of a transformer may be located where? PP300
But must do what?
May be located at other than than the tranformer, but must....
protect the primary windings (T450.3B) and the conductors (240.4)
According to 240.21(C)1 of the 2017 NEC, the transformer secondary is not permitted to be protected by the primary ocpd unless it is one of the following transformer connections. PP310
When primary protecton includes sencondary protection, what ratio must be used? Controls what? PP311 NEC 240.21C1
Transformer ratio (must not exceed the transformer secondary conductor ampacity by the secondary to primary transformer voltage ratio). and controls the size of the conductors used on the secondary of the transformer.
The basic rule for feeder taps on transformers (240.21) states that the OCPD is required to be connected where? PP313
Where the conductor recieves its supply
Tap rules allow what? PP313
Exceptions that allow the tap to not have an OCPD at the point where the conductors recieve thier supply
The length of a tap is from what to what? PP314
Secondary conductors are sometimes refered to as tap conductors? T/F PP 315 the
from the feeder to the OCPD, and not the transformer
False
...however in ECM magazine "Understanding the Rules for Feeder Taps" Mike Holt | Jun 01, 2002. He claims that all transformer secondaries are tap conductors and "apply to every transformer installation". Which is true if the transformer secondary does not exceed 10 ft, or 25ft in supervised industrial installations. But primary OCPD would use a secondary to primary voltage ratio (pri/sec) to protect the secondary as well. Often from a Panelboard or switchboard. Referring to the definition of tap conductor we see that it cannot be a service conductor and has over current protection ahead of its supply that exceeds the value usually perminted elsewhere in art. 240.4.
Tap conductors allow what regarding over current protection and ground fault protection location in a circuit? (Upstream and downstream)
Overcurrent protection is downstream and short circuit and ground fault protection is upstream.
(Art 240.2 handbook notes regarding the definition of tap conductor) 2017
What rule is the only rule that permits secondary conductors to land directly onto main lug only-type switch boards or panelboards. pp316
The 10ft tap rule as it pertains to the 10ft secondary conductor rule NEC 240.21C2.
regarding fire pumps, what type of overcurrent protection is allowed on the secondary of the transformer? PP327
None. Primary ocpd only and it must be sized at 125% of the pump, and all accessories in the circuit and be able to provide locked rotor currents indifinetly. NEC 695.5B
Note 1 on table NEC 450.3(B) for OCPD for primary and secondary conductors for transformers under 600v allows rounding up to the nearest OCPD and what for conductor ampacity?
rounding down for conductor ampacity
What is the definition of an AC alternator? NJATC ATP, Motors 2nd edition, AC alternators, PP 56
A synchronous machine that produces AC current.
Portable Alternators are usually called generators, though a generator produces what type of current? NJATC ATP, Motors 2nd edition, AC alternators, PP 56
DC.
A rotor has ________ and an armature has ________. NJATC ATP, Motors 2nd edition, AC alternators, PP 56
slip rings.
a commutator.
Although an armature is in both a generator (DC) and an alternator. The armature is not always the revolving part but always has the voltage induced into it. (AC) The power-producing component of an electrical machine. In a generator, alternator, or dynamo the armature windings generate the electric current. The armature can be on either the rotor or the stator. -Wikipedia
The commutator is the ring divided into segments, The armature by definition does not necessarily turn (in AC) but is the place where generated voltage is collected.
The rotor in an AC alternator may also be referred to as? NJATC ATP, Motors 2nd edition, AC alternators, PP 56
an alternator.
What turns the rotor shaft and creates a potential in the stator? NJATC ATP, Motors 2nd edition, AC alternators, PP 56
Prime mover.
In a motor the rotor and stator are the core, but in an alternator the core is what? NJATC ATP, Motors 2nd edition, AC alternators, PP 56
many thin laminated sheets of iron pressed together.
The number of poles, combined with the ac line frequency (Hertz, Hz), are all that determine the no-load revolutions per minute (rpm) of the motor. So, all four-pole motors will run at the same speed under no-load conditions, all six-pole motors will run at the same speed, and so on.
The mathematical formula to remember in helping make this calculation is? Source: https://www.achrnews.com/articles/84983-how-to-determine-speed-for-an-ac-induction-motor
The mathematical formula to remember in helping make this calculation is the number of cycles (Hz) times 60 (for seconds in a minute) times two (for the positive and negative pulses in the cycle) divided by the number of poles.
Therefore, for a 60-Hz system, the formula would be:
60 x 60 x 2 = 7,200 no-load rpm /number of poles.
For a 50-Hz system, the formula would be:
50 x 60 x 2 = 6,000 no-load rpm / number of poles.
In a 3 phase and two phase alternator, the windings consist of coils of copper wire placed how far apart electrically? NJATC ATP, Motors 2nd edition, AC alternators, PP 56
120 degrees in 3 phase or poly phase and 90 in two phase.
Coils in an alternator are replaceable in the field? T or F. NJATC ATP, Motors 2nd edition, AC alternators, AC alternators, PP 56
Yes, they are usually individually bolted together so that you can replace any one.
The stator in an alternator consists of what? Does it move? NJATC ATP, Motors 2nd edition, AC alternators, PP 56
Core and windings. No it is not the moving component.
A rotor uses _________ to allow current to flow through the rotor circuit. NJATC ATP, Motors 2nd edition, AC alternators, PP 57
brushes and slip rings.
Slow moving alternators with multiple poles use what to take advantage of low centrifugal force? NJATC ATP, Motors 2nd edition, AC alternators, PP 57
At what speed are these no longer used?
salient poles: poles that project out from the rotor, by definition. Salient: prominent or conspicuous
1800 RPM.
An alternator where the magnetic field is created in the rotor defines what kind of alternator? NJATC ATP, Motors 2nd edition, AC alternators, PP 58
revolving-field alternator.
In a revolving field alternator, what kind of power is used to supply power to the rotor, resulting in the need for what standard components associated with this kind of power? NJATC ATP, Motors 2nd edition, AC alternators, PP 58
D.C. power to the rotor which results in the need to use a brushless exciter.
A brushless exciter is what? NJATC ATP, Motors 2nd edition, AC alternators, PP 58
a brushless exciter is a rectifier assembly mounted on the main rotor shaft along with the exciter generator, on a revolving field alternator.
An exciter generator is what? NJATC ATP, Motors 2nd edition, AC alternators, PP 58
an assembly consisting of a small three phase alternator used to supply current to an alternator rotor, on a revolving field alternator
In a revolving field alternator, the exciter rotor spins as a result of what? NJATC ATP, Motors 2nd edition, AC alternators, PP 59
In this motor the exciter rotor spins as a result of DC field supplied by a stationary set of coils that provide the flux. The exciter may or may not spin, and is referred to as the exciter. NJATC, AC Theory 2009, PP 40
A fixed magnetic field is created in the stator, with the rotor turning within the stator, defines what? NJATC ATP, Motors 2nd edition, AC alternators, PP 59
revolving-rotor alternator, using slip rings and brushes.
A revolving rotor alternator supplies power how? NJATC ATP, Motors 2nd edition, AC alternators, PP 59
A revolving rotor alternator supplies AC power through the rotor slip rings and brushes.
What is the downfall of a revolving rotor alternator and thus the reason they are rarely used today? NJATC ATP, Motors 2nd edition, AC alternators, PP 59
Revolving-rotor alternators work well for lower voltages and currents but cannot handle large voltages and currents because of the difficulty of insulating the slip rings.
A voltage that is too low can cause what? NJATC ATP, Motors 2nd edition, AC alternators, PP 59
inductive loads to draw excessive current.
The three factors controlling the output voltage of an alternator are what? NJATC ATP, Motors 2nd edition, AC alternators, PP 59
length of wire
speed of rotor
strength of the magnetic field
Voltage in an alternator is directly proportional to what? NJATC ATP, Motors 2nd edition, AC alternators, PP 59
The simplest answer is the number of turns. It is also dependent upon the voltage regulator, amount of magnetism, and speed of the rotor, and Tortola length of wire.
Define field windings. NJATC ATP, Motors 2nd edition, AC alternators, PP 59
In a AC alternator, the field windings allow what?
electromagnetic coils that provide the DC for the exciter.
They allow the voltage regulator to control the field at the field winding and thus the output voltage of the alternator.
Most of the alternators in service today are what? NJATC ATP, Motors 2nd edition, AC alternators, PP 60
self excited meaning they get the power for the exciter from their own stator.
The frequency output of an AC alternator must be kept _______. NJATC ATP, Motors 2nd edition, AC alternators, PP 61
constant.
The two factors controlling the output frequency of an alternator are what? NJATC ATP, Motors 2nd edition, AC alternators, PP 60
number of poles and speed of the rotor
AC generator (actually an alternator) speed is calculated using what formula? NJATC ATP, Motors 2nd edition, AC alternators, PP 60
S= (120 x F)/ poles is wrong... this formula should assume HZ x 60 seconds x 2/ number of poles. A very old description of alternating current systems sometimes give the frequency in terms of alternations per minute, counting each half-cycle as one alternation; so 12,000 alternations per minute corresponds to 100 Hz.
Each rotation in a single-phase AC alternator produces what? NJATC ATP, Motors 2nd edition, AC alternators, PP 61
one phase of electricity. Or a complete cycle.
Three phase AC power is generated by? NJATC ATP, Motors 2nd edition, AC alternators, PP 63
rotating three coils through the magnetic field.
The three phases in an AC alternator are electrically 120 degrees apart because? NJATC ATP, Motors 2nd edition, AC alternators, PP 64
Because the rotor windings are 120 degrees mechanically apart.
The prime mover in an alternator is what? NJATC ATP, Motors 2nd edition, AC alternators, PP 64
The power source used to create the relative motion between the coil and the magnetic field.
Alternators are rated in what and at what power factor? NJATC ATP, Motors 2nd edition, AC alternators, PP 64
For this reason the KVA rating of an alternator is equal to what?
KW at a power factor of 80 percent.
125 percent of the KW rating.
AC alternators may be cooled by what? NJATC ATP, Motors 2nd edition, AC alternators, PP 65
Air, water, or hydrogen.
Alternators are placed in parallel or series to carry added load? NJATC ATP, Motors 2nd edition, AC alternators, PP 65
Parallel.
Common methods for manual synchronization include? NJATC ATP, Motors 2nd edition, AC alternators, PP 65
the use of a synchrosocope or the use of synchronizing lights.
With automatic synchronization, a controller monitors what? NJATC ATP, Motors 2nd edition, AC alternators, PP 67
Frequency, phase angle, and voltage of the incoming source and the busbar. This must be done before a generator can be switched into the circuit.
Typically how much extra output power is recommended for a generator? NJATC ATP, Motors 2nd edition, AC alternators, PP 69
25 to 50 percent. Generators are provided with an 80% Power Factor (PF) for this reason. They are over-rated on purpose.
A single phase alternator and a three phase alternator use how many coils to generate a single or 3 phases?NJATC ATP, Motors 2nd edition, AC alternators, PP 70 Summary
Single phase is one coil and three phase is three coils.
It’s important to understand that in a series circuit, current is identical through (how many) circuit elements of the circuit.
ALL. While voltage and resistance are additive in a DC series circuit.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 NEC. PP 36
(how many wire)_____________ series circuits are often used to give a signal something has occurred. They can indicate that a door is open. process is operating, or that there’s fire or smoke, for example.
Two-wire closed-loop accomplish this. Note: If you hear “series” then that should automatically imply a closed loop system versus parallel which is an open loop system.
Resistance opposes the flow of electrons. In a series circuit, the total resistance is equal to the sum of?
In this type of circuit the the sum of all the series resistances. Resistance is additive.
The internal wiring of many types of equipment is connected in series. example, an 115/230V dual-rated motor connected to a 230V circuit must have the internal windings connected in _______so that each winding will receive at least 115v
Series is the connection for this type of 115/230V rated motor.
opposition (resistance) to current flow (amperes) results in a drop of the circuit voltage (voltage drop), and is calculated by the formula ________ for a purely resistive DC circuit.
E vd=IxR is the formula for this
If the voltage is doubled, the power will ________. If the voltage is decreases 50% the power will decrease to 25% of its original value.
The power will increase 4 times if this is doubled.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 NEC. PP 19
What law states that in a series circuit, the sum of the voltages across all of the resistors (or “voltage drops”) in series circuit is equal to the applied voltage?
Kirchoff’s Voltage Law states this.
voltage is additive in a series circuit. (remember current is constant and resistance is additive) Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 NEC. PP 36
Kirchoff’s Current Law states?
that the sum of currents flowing into a junction (parallel is a junction) equals the sum of currents flowing away from the junction is stated by this law. Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 NEC. PP 38
The Law of Conservation of Energy states?
The power supply (a battery, and so forth ) will only produce as much power as that consumed by the circuit… is stated by this law.
Calculate the total resistance (Rt) of the circuit: What is the formula for a series circuit?
What is the
Rt=R1+R2+R3+R4 Is the additive formula for a series DC circuit.
What is also called “open-loop systems,” and are used for fire alarm pull stations and smoke detectors?
parallel circuits are also know as this type of loop system.
There are three basic formula methods of calculating the total resistance of parallel circuit. What are they?
The Equal Resistance method, the Product-Over-Sum , and the Reciprocal method… are the 3 ways to solve for this in a parallel circuit, versus a series circuit where it is the only additive.
What method can be used to determine the resistance total for more than two resistors in a parallel circuit, but what must be done?
only two resistors can be dealt with at a time using the product over sum formula to determine the resistance total.
Rt=(R1xR2)/(R1+R2)
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 NEC. PP 40
In a parallel circuit, the total circuit resistance is always less than what?
Total circuit resistance is the smallest, while individual resistance, is always more than the total resistance in a parallel circuit.
The advantage of the Reciprocal method in determining the total resistance of a parallel circuit is that?
this formula can be used for as many resistors as the parallel circuit contains.
_______circuit has two or more paths through which current flows.
A parallel circuit has this current path.
When power supplies are connected in parallel, the voltage and current does what? In a DC circuit.
voltage remains the same but the current increases. In a DC circuit.
The neutral conductor of a 3-wire, 120/240V circuit will carry current only when?
When the circuits are unbalanced, or when the ungrounded conductors don’t have identical current flow, the neutral will carry current in this type of system.
The neutral of a 3-wire circuit from a 4-wire wye (system carries about the same current as?
What is the neutral current formula for a 3 or 4 wire 120/208 and 277/480v system? Use the Acronym AMAP to remember this.
The neutral of a 3-wire circuit from a 4-wire wye system carries about the same current as the phase conductors.
AMAP: Addition Minus the Added Product of each line.
In=√(L1+L2+L3)-
[(L1xL2)+(L2xL3)+(L1xL3)] is the formula for this type of system.
A balanced 3-wire, single-phase or 4-wire, three-phase multiwire branch circuit has unbalanced current flowing only in the ungrounded circuit conductors. Therefore, the circuit voltage drop for the line-to-neutral only includes the voltage drop of one conductor. The line-to-line voltage is found by what formula?
multiplying the line-to-neutral voltage drop by 1.732 will find the circuit voltage drop for the line to neutral in a both of these wire systems. PP49
Because of the dangers associated with an open neutral conductor, the NEC specifies that the continuity of the neutral conductor of a multi wire branch circuit can’t be dependent upon any wiring device NEC [300.13(B)] - In other words, the neutral conductors of a multiwire branch circuit must be?
spliced together, and a wire (pigtail) brought out to the device. s way, if the receptacle is removed, it doesn’t result in an open neutral conductor.
Also…Each muftiwire branch circuit must have a means to simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates NEC [210.4(B)].
each multiwire branch circuit must have a means to simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates [210.4(B)]. What mitigates this?
individual single-pole breakers with handle ties identified for this purpose, or a breaker with a common internal trip, can be used for this application [240.15(B)1]. PP51
To eliminate the need for gigantic sized heater elements and associated overload relays, what is used?
Current Transformers are used (pis. 129)
Current Transformers are standard on what size starters?
NEMA size 5 and larger starters. Motor Controls- Richard Cox, 2nd edition. PP11
60HP for 240 volt and 125HP for 480 volt motors start at NEMA size 5.
Caution: The secondary of a Current Transformer must always have a burden (load) connected; an open-circuited secondary can result in the development of a dangerously high secondary voltage. Energized but unused CTs must be kept________?
The secondary of these must always be kept short circuited to avoid a buildup of high voltage.
All Current Transformers are ________polarity.
Polarity refers to the instantaneous direction of the primary current with respect to the secondary Current and is determined by the way the Transformer leads are brought out of
the case.
All current transformers are subtractive polarity. Meaning the transformer taps are adjacent to each other. Most (larger) transformers are wound subtractively because the winding can be made slightly smaller and you can get a slightly more effective transfer of the magnetic flux between windings. It also helps keep the induced voltage in the core to a minimum.
On subtractive polarity Transformers the H1 primary lead and the X1 secondary lead will be on which side of the transformer?
the same side of the Transformer (the left side when facing the low-side bushings). All of these have subtractive polarity, meaning they are polarity sensitive.
Current Transformers are unique for what reason regarding windings? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special Transformers, PP 193
Because these usually have only one winding they are unique. The primary is connected in series with the line load.
The primary winding may consist of a straight conductor passing through the center of the magnetic circuit. This straight conductor represents a?
one turn winding.
Therefore, a Current Transformer should always have what done to the secondary when not connected to an external load?
This must never be allowed to be open when the primary circuit is energized.
When the circuit is operational, the load on the secondary keeps the magnetizing Currents low, keeping turn to turn potential low. The secondary should be shorted when?
not connected to an external load.
Three types of Current Transformers in general use are what? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special Transformers, PP 195
Window, bar, and wound (toroidal).
A Transformer that consists of a secondary winding wrapped around a core and a primary sent through the opening in the core. ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special Transformers, PP 195
Window Current Transformer.
A special type of window Current Transformer with a solid bar placed permanently through the window is what? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special Transformers, PP 195
A Bar Current Transformer.
A Bar Current Transformer is found in installations where the potential is what KV or less? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special Transformers, PP 195
These Transformers are found in installations 25KV or less.
This type of Current Transformer is found in the high-voltage side of substations and has a primary conductor the carries the Current and a low turn secondary for the output Current. ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special Transformers, PP 195
Wound Current Transformer.
A Transformer with separate primary and secondary windings wrapped around a laminated core. ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special Transformers, PP 195
What is the Current Transformer. Keep in mind that the wire passing through the CT or the busbar acts as a one turn Primary Winding.
CT’s are also used with what to provide an analog signal? What is an analog signal?
CT’s are also used with current transducers to provide an analog signal. Source: http://www.metersusa.com/Transformers/Data/CTTheory.pdf
Are CT’s safe to use with motor inrush current?
Yes, they are specifically designed to do this. Source: http://www.metersusa.com/Transformers/Data/CTTheory.pdf
The secondary of a Current Transformer is always rated at what amperage? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special Transformers, PP 197
At 1 or 5 amps on the secondary regardless of the Current rating of the primary.
The relationship of the ratio of primary and secondary turns is expressed in the following
formula:
Actual= (ratio +/- X1 turns/H1 turns)
Where H1 is primary and X1 is secondary: see below imageOr in engineering lingo….
Ka = (Kn ± Nsa) / Np
Ka = Actual transformation ratio
Kn = Nameplate transformation ratio
Transformation ratio = primary current / secondary current
Nsa = Number of secondary turns added or subtracted
Np = Number of primary turns
Ka = (Kn ± Nsa) / Np
= (10 + 2) / 3
=4
Actual CT Ratio = 20:5
How do you add or subtract to the ratio for a CT using the H1 and X1 subtractive relationship?
To Add: loop X1 lead through H1. To Subtract -loop X1 opposite H1
The external load (e.g., meters, transducers, etc.) applied to the secondary of a CT is called the burden. The burden can be expressed in volt-amperes using the following formula.
Common applications of Current Transformers include what? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special Transformers, PP 197
Power metering, motor Current monitoring, and variable speed drive monitoring are common applications for this type of Transformer.
On new construction, size the CT to handle about ?% of the circuit breaker capacity. Source: http://www.metersusa.com/Transformers/Data/CTTheory.pdf
On new construction the CT should be sized for 80% of the feeder amperage circuit breaker capacity. for example: the building is served by a 2000 amp breaker, use 1600 amp (2000 x 0.8) CT’s. This makes sense in that breakers are sized for 125% of a continuous load and that means the CT at 80% of the breaker is equal to 100 percent of the actual current.
CT’s that are used to monitor motor loads can be sized from?
Motor starters have these type of Transformers on the lines.
What has Current Transformers on the lines to the starter to monitor the motor Currents? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special Transformers, PP 197
In power metering a Current Transformer provides what in comparison to a potential Transformer? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special Transformers, PP 197
The Current Transformer provides a way to measure the Current, and a potential Transformer provides way to measure the voltage in this type of metering.
What is part of instantaneous electronic trip IET circuit that takes the drive off-line if a sudden rise in Current occurs that exceeds the rating of the drive? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special Transformers, PP 197
Variable speed drive Current Transformers that monitor the incoming Current is part of this.
A Current Transformer is used to do what? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special Transformers, PP 201
This Transformer is used to step down a high Current to make it easier to measure.
A Current Transformer is used to step down the line Current to make it easier to measure, thus creating what type of voltage Transformer? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special Transformers, PP 193
A modified step-up voltage Transformer. Since the power on the primary and secondary of a Transformer is the same.
Nearly all relays are operated from what? Keith H. Suker, Power Electronics design: a practitioner's guide, PP 18 (NC set: Switchgear)
Current Transformers and most are now solid state.
Due to this type of arrangement, the current transformer is often referred too as a?
“series transformer”
There are a variety of metering applications and uses for current transformers such as with?
Wattmeter’s, power factor meters, watt-hour meters, protective relays, or as trip coils in magnetic circuit breakers, or MCB’s.
In most current transformers an approximate inverse turns ratio exists between the two currents in the primary and secondary windings. This is why calibration of the CT is generally for?
a specific type of ammeter.
As well as the handheld clamp type CT, split core current transformers are available which has one end removable so that the load conductor or bus bar does not have to be? And what are their amperage range?
disconnected to install it. These are available for measuring currents from 100 up to 5000 amps, with square window sizes from 1″ to over 12″ (25-to-300mm
Current transformers are intended to be used as proportional current devices. Therefore a current transformers secondary winding should never be operated into an?
open circuit, just as a voltage transformer should never be operated into a short circuit.
The CT voltage class determines?
the maximum voltage the CT may come in direct CONTACT with. For example, a 600V window CT cannot be installed on or around a bare 2400V conductor, however a 600V window CT can be installed around a 2400V cable, if the CT is installed around the insulated portion of the cable and the insulation is rated correctly.
The polarity of a current transformer is determined by?
the direction in which the coils are wound around the core of the CT (clockwise or counter clockwise), and by which way the secondary leads are brought out of the transformer case.
All current transformers are subtractive polarity and will have the following designations to guide proper installation:
◦ H1 - Primary current, line facing direction
◦ H2 - Primary current, load facing direction
◦ X1 - Secondary current (multi ratio CTs have additional secondary terminals)
On subtractive polarity transformers, which are CT's, the H1 primary lead and the X1 secondary lead are?
on the same side of the transformer.
CT polarity is also sometimes indicated with an arrow. These CTs should be installed with the arrow pointing?
in the direction of current flow.
The polarity marking on electrical drawings may be made for current transformers in several different ways. The three most common schematic conventions are dots, squares, and slashes. Polarity markings on electrical drawings represent H1, which should be facing?
the source.
The extent to which the secondary current magnitude differs from the calculated value expected by virtue of the CT ratio is defined by?
the accuracy class of the CT.
Regarding the Secondary current magnitude differing from the calculated value expected by virtue of the CT ratio: The greater the number used to define the class, the greater the?
permissible deviation in the secondary current from the calculated value (error).
the ratio of the primary to the secondary currents. For example, a 100/5 CT would not fulfill the function of a 20/1 or a 10/0.5 CT.
The CT accuracy class is comprised of a number-letter-number combination as set forth in ANSI C57.13 and is broken into three parts:
rated ratio accuracy rating, class rating, and maximum burden.
Except for the least accurate classes, the CT accuracy class also defines the permissible?
phase angle displacement between primary and secondary currents.
The second part of the CT Accuracy Class is a letter that designates?
the application for which the CT is rated. A current transformer may have dual ratings and be used in metering or protection applications, if both ratings are listed on the nameplate.
The third part of the CT Accuracy Class is the?
maximum burden allowed for the CT. Like all transformers, a current transformer can only transform a finite amount of energy.
The energy limitation of a CT is referred to as the?
maximum burden. If this limit is exceeded, CT accuracy is not guaranteed.
Relay class CT burdens are expressed as?
volt-amperes and are displayed as the maximum secondary voltage allowable if 20 times the CT rating (100A for a 5A secondary CT) were to flow through the secondary circuit.
Relay class CT burdens are expressed as volt-amperes and are displayed as the maximum secondary voltage allowable if ______x the CT rating (100A for a 5A secondary CT) were to flow through the secondary circuit.
20 times the CT rating
What can be done to alleviate too much inrush into a metering CT used for large breaker trip, where the breaker CT signal causes a trip repeatedly?
A larger CT ratio or more iron in the CT will help this tremendously. Larger wires over long runs may help with CT burden by lowering the resistance and increasing current and voltage, since voltage and current are directly proportional.
which is easier to transform? AC or DC? NJATC, AC Theory 2nd edition, 2009, WB 9
AC
Each time an alternator completes one complete 360 degree rotation it is called what? NJATC, AC Theory 2nd edition, 2009, WB 10
A cycle
In an AC generator what changes to cause polarity changes? NJATC, AC Theory 2nd edition, 2009, WB 10
The flux field (left hand rule)
When a conductor cuts the magnetic flux lines at ___ degrees, the maximum voltage will be induced into the conductor. NJATC, AC Theory 2nd edition, 2009, WB 11
90 degrees
The time required for one cycle or two alternations is what? NJATC, AC Theory 2nd edition, 2009, WB 12
A period
What is the average AC voltage for a full cycle of a perfect sine wave? NJATC, AC Theory 2nd edition, 2009, WB 12
zero, because the average is the actual average of all peak values across a full cycle.
Current flow from a battery is generally considered from what polarity to what? NJATC, AC Theory 2nd edition, 2009, WB 34
- to +
The left hand generator rule uses the thumb, forefinger, and the next finger, representing what? NJATC, AC Theory 2nd edition, 2009, WB 34
thumb: motion
Forefinger: field
Next finger: current
A general rule of thumb for ignoring inductance or capacitance in field resistive calculations is what? NJATC, AC Theory 2nd edition, 2009, WB 37
Generally at 50-60 HZ electricians in the field will ignore inductive or capacitive elements in resistive calculations, but at higher frequencies you cannot. Also, if you answered the resistance is 1/10th or less the inductance then you are also correct.
An AC circuit is solved at 50 to 60 HZ like a DC circuit but uses what type of AC value? NJATC, AC Theory 2nd edition, 2009, WB 37
However: Effective alternating-current voltage or effective ac current is the equivalent value of direct-current voltage or dc current that will produce the same amount of heat in a resistor. Mike Holt’s Illustrated Guide to Electrical Exam Preparation, Based on the 2014 NEC PP 68
RMS or effective
Peak = 1.414(RMS/eff) a.k.a. max instantaneous value
Effective (RMS) = .707(peak)
Average = .637(peak)
Peak to peak = 2(peak)
Current and voltage in an AC purely resistive circuit are in or out of phase? NJATC, AC Theory 2nd edition, 2009, WB 37
in
The opposition to current change is called what?
This opposition to current change is called reactance, rather than resistance; which would be the opposition to current.
What two factors not present in a DC circuit affect the opposition to current flow in an AC circuit? NJATC, AC Theory 2nd edition, 2009, WB 38
Eddy currents and skin effect: remember that skin effect increases as the frequency increases. I.E. harmonics.
Concerning induced voltage and applied voltage, these two elements are how far out of phase with one another? NJATC, AC Theory 2nd edition, 2009, PP 49
Applied voltage and induced voltage (CEMF) are 180 degrees out of phase with each other
Capacitors oppose a change in?
Voltage.
Inductors oppose a change in what? NJATC, AC Theory 2nd edition, 2009, PP 50
basic rule: Inductors always oppose a change in an AC current.
How many time constants does it take for circuit current to reach its maximum value in an inductive circuit? What is this Maximum value? NJATC, AC Theory 2nd edition, 2009, WB 42
5 time constants
Maximum value is considered 99.5%
Does a coil change its henry value with a change of frequency or a change in the current value? NJATC, AC Theory 2nd edition, 2009, PP 55
NO
The Henry is the unit of measure for inductance. A coil has an inductance of 1 henry when...? NJATC, AC Theory 2nd edition, 2009, PP 52
...a current change of one ampere per second causes an induced voltage of 1 volt.
The formula for determining how much CEMF is produced is what? Remember: The voltage created by an inductive load is not proportional to the amount of current flow, but rather to the rate at which current is changing. AC Theory, NJATC 2009 PP 54
CEMF = -L xΔ I Δ T
where L is inductance, I is current, and T is time
The greater the inductance, or the faster the rate of change of current, the greater the CEMF
In a purely inductive circuit the current lags behind the applied voltage by? NJATC, AC Theory 2nd edition, 2009, PP 57
90 degrees
What is the phase relationship between CEMF to applied voltage and current to applied voltage? AC Theory, NJATC 2009 PP 58
CEMF is 180 degrees out of phase with applied voltage and the current lags the applied line voltage by 90 degrees. However:CEMF either opposes or aids conductor current flow. As alternating current increases, the polarity of the induced volt(CEMF) within the conductor opposes the conductor’s current and tries to prevent the current from increasing. But, as alternating current decreases, the polarity of the induced voltage (CEMF) within the conductor aids the conductor’s current and tries to prevent the current from decreasing. This is also known as VAR or volt amps reactive.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP74
The angle that the current lags the voltage through the coil is what? AC Theory, NJATC 2009 PP 61
The same angle the impedance vector makes in relation to the resistance vector.
When doing quick approximations for the impedance of a coil the ratio of the inductive reactance to the resistance is considered. If the resistance is less than ______ of the Xl, then we disregard the R and claim the total opposition of the coil is made up of reactance. AC Theory, NJATC 2009 PP 67
1/10th
Concerning coefficient of coupling, when voltage across the primary of a transformer does not reach the secondary in its entirety, what is this defined as? Source: http://www.tpub.com/neets/book2/5f.htm 2015
LEAKAGE INDUCTANCE is assumed to drop part of the applied voltage, leaving less voltage across the secondary.
Concerning a transformer and coefficient of coupling; since the counter emf in the primary is equal (or almost) to the applied voltage, a proportion may be set up to express the value of the voltage induced in terms of the voltage applied to the primary and the number of turns in each winding. This proportion also shows the relationship between the number of turns in each winding and the voltage across each winding. This proportion is expressed by the equation: Source: http://www.tpub.com/neets/book2/5f.htm 2015
The total amount of mutual induction M is calculated by the formula? AC Theory, NJATC 2009 PP 68
M=K x √(L1xL2)
Where M=mutual induction in henrys
K=decimal equivalent of coefficient of coupling
The COEFFICIENT OF COUPLING of a transformer is dependent on the portion of the total flux lines that cuts both primary and secondary windings.
Two coils need to be oriented to one another in what way to provide coefficient of coupling and in what way to avoid this. AC Theory, NJATC 2009 PP 68 Tech Tip
Two coils placed parallel to one another to create a mutual induction or perpendicular to avoid it.
What is referred to as the Q of a coil? AC Theory, NJATC 2009 PP 70
Represented by what formula?
The quality factor
Q=XL/R
In an impedence triangle the angle theta represents what? AC Theory, NJATC 2009 PP 71
It represents the actual angle of lag that the current lags behind the voltage in the circuit. Also known as power factor.
Normally the lagging angle of current is not measured in the residential application, but that same angle is measured and may be charged for if it is too large in what type of accounts? AC Theory, NJATC 2009 PP 72 Tech Tip
commercial accounts
In a voltage triangle, what are the following parts? AC Theory, NJATC 2009 PP 77
Hypotenuse ?
Adjacent ?
Opposite ?
When a circuit containing both resistance and inductance is connected to alternating current, the total current will lag the applied voltage at an angle between 0 and 90. The exact amount of the phase angle difference is determined by what ratio? AC Theory, NJATC 2009 PP 78
ratio of XL/R
What is defined as energy stored in a magnetic field or an electrostatic field and is returned to the circuit as the fields diminish. AC Theory, NJATC 2009 PP 80
Reactive power
power factor is the cosine of theta in which triangles? AC Theory, NJATC 2009 PP 80
impedance, voltage, and power
The movement of the magnetic field is energy and that energy is stored in the magnetic field is a statement that best describes what term? AC Theory, NJATC 2009 PP 80
Reactive power measured in volt amps
The power factor is an angular measure. True or False. AC Theory, NJATC 2009 PP 82
False, the power factor is a ratio.
T/A
R/Z
W/VA
The amount of time required for the current flow to reach the maximum value is expressed in time constants. In a circuit with inductance and reactance, the time constant is defined from the following formula. AC Theory, NJATC 2009 PP
T=L/R
Where T= time constant in seconds
L= Circuit inductance in henrys
R= Circuit resistance in ohms
Note: The first time constant is 63.2 percent of max current and takes 5 time constants for 99.2 percent of current to rise or decay.
The time constants are used for what purpose? AC Theory, NJATC 2009 PP 85
The time constants are used to protect a circuit from the voltage spike caused by a collapsing inductor magnetic field, which may ruin other circuit components.
The general formula for Voltage Drop in a single phase system is? And in a 3 phase system? And lastly in a DC system?
single phase VD=2KLI/CM
Three phase VD=1.73KLI/CM
DC system VD=I(R)
Electrical pressure is measured in what?
volts
A thermocoupler will transform what into electricity and is used where?
Heat. Is used in a water heater as a switch.
A rectifier is used to change what?
What must be used to solve what problem created by a bridge rectifier used to turn AC into DC?
AC to DC. I.e. full wave rectifiers and not a half wave rectifier.
A capacitor in parallel with a resistor can be used to level out the pulsating dc current into a filtered DC current.
Connecting four rectifiers into the full-wave rectifier circuit shown provides a bridge circuit which allows different rectifiers to alternately provide current to the load during each half of the sine wave alternation, while always keeping the same direct-current polarity on the load. This provides a partial solution, however the current produced is not a pure dc current, but what’s called “pulsating dc current”
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 NEC PP 69
Capacitance is measured in what?
Farads
Capacitance Reactance is measured in what?
ohms
Storage batteries are rated in what? And based on a discharge rate for how many hours?
amp-hours and usually at 20 hours discharge rate versus a starting battery that uses a 10 hours discharge rating.
explained: because of the Peukert effect (aka, The faster a battery is drained, the less overall amperage is available), if you discharge a battery over the course of 100 hours, the AH rating looks higher that if you discharge that same battery over the course of 1 hour. So, there has to be a standard. For deep cycle batteries the standard rating is 20 hours. So, if a battery has a rating of 100AH @ 20 Hr rate, then that battery was discharged over 20 hours with a 5 amp load. Starting batteries on the other hand, are typically rated at 10Hr rate, because they are used faster, so the 20Hr rate is not as important.
It is customary to speak of the electromotive force as the ________of the circuit.
voltage
Electricity produced by means of a pressure to a material is called?
piezoelectricity. An example is FLE switching used in title 24 California advanced lighting which uses milliamps from finger pressure to wirelessly signal a light to switch via a load controller. This removes the travelers and wire otherwise necessary.
The insulation material in the commmutator of a DC generator between the positive and negative bars is made of?
Mica
An A.C. generator is also called what?
An alternator.
A DC generator can be built with much larger voltage ratings than AC? T or F
False. Remember a DC generator uses a commutator and this limits the amount of current output. Peak voltage is 1.414 times RMS or effective multiplied by 2 again equals AC peak to peak. This would be the same as 2.828 times RMS or effective which is essentially DC. In other words an AC revolving field generator can produce 2.28 times the voltage of a DC generator but produce the same heating effect.
A voltmeter measures what?
The effective voltage difference, which can be line to ground, line to neutral, or line to line. And is always placed in parallel with the circuit.
What is the most widely used generator today?
Revolving field AC generator. The term generator is misleading. Here is why.
Generator is a generic class of devices, while the alternator is a type of generator producing AC current.
• Alternators use voltage regulators and rectifiers to create a DC output, while in other generators DC current is obtained by adding a commutator or AC current is produced.
• Alternator output can have varying frequencies due to changes in the rotor frequency (but it has no effect because the current is rectified to DC), while the other generators are operated to a constant frequency of the rotor shaft.
• Alternators are used in automobiles, to generate electrical power.
A voltmeter is connected in what way with the circuit? Versus an ammeter?
parallel is the way in which this is connected to a circuit. An ammeter is connected in series in only a DC circuit where a clamp-on CT or clamp style ammeter is used in AC. However induction can be picked up with a CT, but only when the load is pulling current. CURRENT SHOULD NEVER BE CHECKED TO SEE IF A CIRCUIT IS ENERGIZED OR NOT.
What is measured in henrys?
inductance
Inductive reactance is measured in what?
ohms
A generator exciter uses what type of current?
Direct
A nuetral carries what? So a broken neutral will always have higher or lower voltage across the lower watt load?
The unbalanced load back to the source. A broken nuetral will always have a higher voltage across the lower watt source.
Ohm's law applies only to what type of circuit?
Purely resistive.
What operates under the principal of electro-chemistry?
batteries operate under this principal.
The NEC under article 480 and definitions has a fine print note that denotes “The most common nominal cell voltage 2 volts per cell for the lead-acid systems, 1.2 volts cell for alkali systems, and 3.6 to 3.8 volts per cell for Li-ion systems. Nominal voltages might vary with different chemistries.”
Resistance is proportional to length and diameter of a conductor how?
Resistance is directly proportional to length and inversely proportional to diameter of this.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP74
These currents are stray currents that consume power and oppose current flow. They are produced by the expanding and collapsing magnetic field of alternating current circuits.
Eddy currents are produced by these.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP74
When the conductor is _______, the flux lines cut through the conductor at more than point. This increases the CEMF by self-induction.
When the conductor is coiled this happens with regards to magnetic flux.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP76
Down stream conductors shall be used where in regards to architectural changes?
at architectural elevation changes, generators, water towers, and cooling towers. Main down leads may be used on building steel.
An air terminal is to be what size in diameter and of what type of metal?
1/2" in diameter and atleast 12" above the protected area, but 24" long.
Air terminals are to be spaced how far apart?
25 feet maximum spacing with 24" high terminals along the roof edge and no greater than 50ft across roofs or laterally.
Bonding to structural steel for lightning protection for use as a down conductor is allowed every how many feet?
every 100ft max. at roof level and 60ft or less at grade.
How often are downleads supported?
every 3ft.
What is the minimum bending radius for one 90 degree bend for a down conductor?
8" radius minimum
Air terminals will be located a maximum of how far from the roof edge?
2ft.
Any equipment within what distance of the lightning protection system should be bonded?
Anything of a metallic nature including gas mains at within 6ft of the lightning protection system.
copper should not be mounted on what galvanic surfaces?
aluminum surface, bare zinc, or galvanized sheet metal. source: pg 24 of submittal and NEC.
The grounding conductor as defined by NFPA780 should be a minimum of how far into the soil?
30"
The ground rod for the lightning protection should be 5/8 by 8ft long per the NFPA780 2011 publication, but the submittals may exceed this with what size?
3/4 dia. and 10ft long. (since they must be 10ft deep).
A signal then is sent to a ______________, which executes a control action.
The final control element receives this from the primary element.
is the method by which we regulate a particular process?
process control.
The field instruments that gather process data (I e., input devices) and transmit the data to the controller in the form of electrical signals, as well as the output devices?
The I/O devices are.
Typical signals used in process control are of 3 types?
analog, discrete, and digital are the 3 types of this.
analog signal usually represents a range of values read by a sensor. represented by _____volts, ____ mA, a variable pressure (______psi), or by other means.
1-10 volts
4-20mA
3 to 15psi
A marshaling panel connects field wiring to __________. Inputs and outputs are typically assigned a rack, slot, box, or point assignment to terminate field wiring.
controller termination points are usaully located here from field wiring. PP5
Another form of signal used is the discrete signal. What is a discrete signal when it comes to its function?
A discreet signal is simply on/ off, but is always a control signal. Versus binary, which is on and off. An example of discrete control is the application of a sump pump with high and low switches that turn a pump on or off, depending on the level in the sump
The transmission of electronic signals to and from a controller is most often accomplished through the use of what to avoid induction and interference?
Twisted-pair wiring and often shielded. Wires are twisted around each other to negate capacitive and inductive effects on the current flowing in the conductors. PP6
What is often redundant in controls?
communication lines.
The process of adjusting an instrument or component on a deviation chart so that its reading can be correlated to the actual value being measured? PP7
Calibration.
In a shared Controller, the resulting execution of the instructions entered into the controller are referred to as a?
A scan is an execution of the instructions entered into this. PP9
Process tubing is also called what?
Impulse tubing is called this. PP9
Instruments that are used in process control systems are identified by this? PP10
An identification code or tag number identifies this. This unique code lows a device’s function to be determined by locating the tag number on a drawing or specification sheet. The tag number can provide information on how the device operates, its control purpose, and the loop designation it receives.
That part of a loop or instrument that first senses the value of a process?
The primary element is this. PP10
These describe the operational intent of the control loop rather than individual instruments. PP10
function blocks describe this.
Shows all related (loop number) devices for controlling means and the wiring path, termination points, and device locations? PP13
What is a Loop Sheet.
A record of devices listed by tag number showing ranges set points material construction process exposure and related environmental variables is?
A spec sheet. PP13
This usually only indicates termination points of controlling means?
Elementary drawing does this. PP13
Array of values over which a transmitter is intended to measure and is indicated by Engineering Units of measurement? Versus a span, which is just an upper and lower limit range.
what is a range. PP20
correctly analyzing determines whether the necessary steps to adjust the transmitter are needed. This process, known as __________, simulates the process the instrument will measure and determines whether corrective action is needed. PP20
Bench calibration is simulates this process.
To properly perform an instrument calibration, it is necessary to understand the concepts of ________and _______of an instrument’s input and output signals. PP20
range and span must be understood to properly perform this.
Accuracy equals? PP21
deviation/span=accuracy percent (x100).The difference between true and measured values, divided by the instrument’s span and multiplied by 100. equals accuracy in a percent.
Precision is the repeatability of an instrument to record the same output signal to its corresponding input. Precision has nothing to do with? PP23
Accuracy has nothing to do with this.
To calculate the accuracy of a transmitter the level of accuracy depends on gain. Gain is the measure of? Represented by what formula? PP22
Consistent output deviation. How much an output could change given the same input change. It is the most important factor used to determine the level of accuracy. Gain = the output/input span.
How do we know when an instrument is correctly calibrated to a certain accuracy and precision? We use standards that establish guidelines for acceptable instrument calibration. For each input and output to a transmitter, what must be used? PP23
An input test standard must be used.. For the output, an output test standard must be applied.
What defines the smallest detectable increases of measurement, usually defined by the smallest reading of bits used? And what testing instrument is an example?PP24
To define a reading of the smallest bits used, defines resolution. A pneumatic calibrator does this.
What may refer to the maximum output deviation from the mean output? And how is this expressed? PP23
Repeatability is expressed as the maximum difference between two readings. Taking the 5 measurements, finding the averaged and then the difference between each two and then find their mean average for each set. These two numbers then give you the maximum output deviation from the mean output.
______ is how closely an instrument reflects its input, and_______ is a term given to an instrument that reflects the same output signal from a constant input signal, time after time. PP23
Accuracy and repeatability.
Calibration can adjust for several types of instrument errors. What are the most common? PP25
Zero shift: deviation is consistent throughout the signal span (difference between the upper and lower limit of a range expressed in the same units)
span error
nonlinearity (proximity of a calibration line to an established straight line)
dead band: The change through which the input to an instrument can be varied without initiating an instrument response.
hysteresis:
Difference between upscale and downscale results in instrument response when subjected to the same input approached from opposite directions.
…are the most common of these.
What is the term for an instrument whose output is consistently higher or lower than the expected value?
Zero shift is consistent throughout output signal span, or to state it correctly, the deviation is consistent throughout the signal span.
____________is performed to verify that an instrument is properly calibrated over its full output signal span. A simulated input is applied at 0%, 25%, 50%, 75% and 100% of the input range.
A five-point check.
For either instrument error, turning the zero adjustment screw can correct the problem. What are the two errors.
These two errors are suppressed or elevated zero shift. PP25
Calibrating an instrument with span errors requires what? PP29
five-point check, then zeroing with the adjustment screw and then correcting span with the span adjustment.
What are the most common errors found in an instrument pp29
Zero and span errors are the most common errors found in an instrument
To correct _______ , the instrument must first be zeroed, and the span is then adjusted. pp29
span is corrected this way.
Define Nonlinearity. PP.29
Proximity of a calibration curve to a specified, straight line, during any one calibration cycle. Nonlinearity produces an output that, when measured and plotted, does not have any consistent error shift between the upper and lower its of its range. A large linearity problem is not correctable, and the instrument must be repaired. In some cases, nonlinearity errors are small enough that their effect is scarcely noticeable, but these errors often increase with time.
Recording output measurements throughout the input range causes different outputs moving up or down is defined as? What device type does this most commonly occur in. PP30
Hysteresis. Which is not commonly found in electronic instruments; it usually occurs in mechanical measuring devices.
Define dead band. PP31
Deadband occurs when the input value can be varied but no visible output change can be recorded. Dead band can be a very small value that is within the tolerances specified.
Is Deadband adjustable? What can be done? PP31
No. When the dead band error becomes significant enough to stray beyond the toll specified, the instrument may be in need of repair. Deadband usually isn’t adjustable, but the error magnitude may be reduced by adjusting the gain of the instrument.
Name this instrument. And what does it do? PP32
decade box. which can be used to simulate the resistance of a load.
Name this instrument. PP32
Wallace and Tiernan portable pneumatic calibrator also called a Wally box.
What is the following instrument? And what does it do? PP32
Yokogawa CA12 Handy Cal, which calibrates resistance temperature detectors (RTD’s) and thermocouples.
The Fluke 744 measure and source pressure using any of 29 fluke _________?
Measure/source pressure using any of 29 Fluke 700Pxx Pressure Modules
What is this a picture of and what is it used with?
700pxx pressure module used with a Fluke model 744 Documenting Process Calibrator (DPC), of which 29 current variations are available.
What is the following a picture of? PP32
A Fluke Model 744 Documenting Process Calibrator.
What is Bandwidth?
What is a symmetrical region around the set point in which proportional control occurs.
What is Baud?
This is a unit of data transmission speed equal to the number of bits per second ( 1,200 ____ = 1,200 bits/sec).
What is a pressure sensor that converts pressure to linear displacement.
What is a bellows.
The need for a pressure-sensing element that is extremely sensitive to low pressures and provides power for activating recording and indicating mechanisms prompted development of this? Most accurate in measuring? PP 37
Metallic bellows pressure-sensing element. The metallic bellows is most accurate in measuring pressures from to 75 psi. Providing power to activate these.
What is the ratio of the diameter of a pipeline constriction to the unconstricted pipe diameter.
What is a Beta ratio.
A term applied to a signal or device that has only discrete positions or states (on/off).
What is binary.
A set of things such as words, characters, digits, or parameters handled as a unit is this.
What is a block.
What is a delay in output change following a change in input.
Lag is this.
This is a straight-line flow of a fluid.
What is Laminar.
Expression of pressure in terms of the height of fluid best defines this term.
Head pressure. PP37
Diameter of the bellows ranges from? PP. 37
0.5 to 12 inches describes the range of this.
In practice, the bellows must always be opposed by _____, and the deflection characteristics reflect the resulting force of the spring and bellows.
a spring must always oppose this. PP 38
A pressure sensor that converts pressure to displacement; a coiled, flattened tube that is straightened when pressure is applied.
What degree span is this tube usually bent to?
What is a bourbon tube? PP38
And is usually bent to 270 to 300 degrees in an arc.
pressure detectors are used to provide up to three basic functions:
indication, alarm, and control are the three basic functions of these? PP 38
UPS systems are designed to integrate easily into the standard electrical infrastructure, so that means smaller power requirements are typically single-phase designs, with larger power requirements being handled by three-phase systems. In America, the typical single-phase UPS design is smaller than_____KVA , while three-phase systems start around 8KVA and go into the MVAs. In some counties in Europe, all systems greater than 8 kVA must have a three-phase input to make sure the utility mains electrical system stays balanced. PP495 Data Center Handbook: 2015, Hwaiyu Geng. Wiley & Sons Inc
In America, the typical single-phase UPS design is smaller than 25KVA
IT systems are at risk even in the largest data centers. Of the 450 Fortune 1000 companies surveyed, each site suffered an average of _____ failures each year. About 28% of these incidents were caused by power problems. PP495 Data Center Handbook: 2015, Hwaiyu Geng. Wiley & Sons Inc
Of the 450 Fortune 1000 companies surveyed, each site suffered an average of 9 of these each year.
____% of companies that experience a computer disaster and don’t have a survival plan go out of business within 18 months. PP 496 Data Center Handbook: 2015, Hwaiyu Geng. Wiley & Sons Inc
90% of companies that experience a computer disaster and don’t have this go out of business in 18 months or less.
UPS designs get a base classification by the actual energy storage/delivery method used. There are two general classifications: What are they? PP 496 Data Center Handbook: 2015, Hwaiyu Geng. Wiley & Sons Inc
static and rotary are the two types of design for these electrical components.
Rotary UPS uses a rotating device (generator) that is typically powered by the utility : through some type of motor system. The rotary generator, sometimes labeled _______, typically a heavyweight flywheel assembly to store energy allows the generator section time to start, and then :>vide power when AC utility power is lost. PP 496 Data Center Handbook: 2015, Hwaiyu Geng. Wiley & Sons Inc
Diesel Rotary UPS (DRUPS) is this.
Mexico and other parts of Central America use what voltage for their standard single-phase distributed voltage. PP 496 Data Center Handbook: 2015, Hwaiyu Geng. Wiley & Sons Inc
In this geographic area, they use 127V for their standard single-phase distributed voltage.
UPS for three-phase applications are typically manufactured 120, 220 Y/127, 480 Y277, and 600 Y/______volt for for North America and 380Y/220, 400Y230, and 415Y/240V for the rest of the world. However, some North American data centers are now deploying 415 or 400V products to operate the IT loads close to their maximum value, driving up the efficiency power supplies. I addition, the entire data center benefits as this eliminates the needs for 480 or 600V to transformers, typically gaining another 1-3% of efficiency. PP 496 Data Center Handbook: 2015, Hwaiyu Geng. Wiley & Sons Inc
347V is the 600y/voltage.
UPS for three-phase applications are always manufactured with wye or delta configurations in North America? PP 496 Data Center Handbook: 2015, Hwaiyu Geng. Wiley & Sons Inc
These electrical power management systems are always manufactured in a wye configuration in North America, versus a popular Delta supplied configuration in Europe, for the purpose of utility balanced phasing.
Static UPS systems include what? For the DC or backup energy source and creates an AC sign wave for the connected load equipment.
These systems include an inverter.
In a UPS static inverter, the low-cost system: use power transistors or _____, higher-cost systems typically use devices called _____.PP496 Data Center Handbook: 2015, Hwaiyu Geng. Wiley & Sons Inc
the low-cost system: use power transistors or MOSFETs, higher-cost systems typically use devices called insulated gate bipolar transistors (IGBT’s)
What is a double conversion three phase UPS and how does it function?
This is the most common type of UPS above 10kVA (Volt-Ampere). Double Conversion On-Line UPS is the same as the Standby UPS except that the primary power path is the inverter instead of the AC mains. failure of the input AC does not cause activation of the transfer switch, because the input AC is not the primary source, but is rather the backup source. Therefore, during an input AC power failure, on line operation results in no transfer time. Source: https://www.sweetwater.com/insync/double-conversion-line-ups/
Does the inverter on a Double Conversion three phase UPS prevent a transfer from dropout by design?
No. The inverter power can also drop out briefly, causing a transfer, if the inverter is subjected to sudden changes in the load, or if the inverter experiences an internal control “glitch”. Contrary to popular belief, Double Conversion On-Line UPS systems do exhibit a transfer time, and in actual installations may transfer as frequently as standby type UPS systems; however on line UPS transfers are not related to AC input power failures as they are in a standby UPS. Source: https://www.sweetwater.com/insync/double-conversion-line-ups/
The input power drawn by the large battery charger in a UPS is what?
The input power drawn by the large battery charger in a UPS is often non-linear and can interfere with building power wiring. Because any electrical system with rectified power creates a triple harmonic.
What is an IGBT?
The IGBT (Insulated Gate Bipolar Transistor) is a semiconductor device with four alternating layers (P-N-P-N) positive, negative, etc. that are controlled by a metal-oxide-semiconductor (MOS) gate structure without regenerative action. they can handle very high voltages and switch very very quickly.
advances in high-power IGBTs (Insulated gate bi-polar transistors) allow switching frequencies for inverters typically less than 50 kVA in size to be above the human audible range, therefore reducing operational noise. What is the human audible range? PP 496 Data Center Handbook: 2015, Hwaiyu Geng. Wiley & Sons Inc
18kHz is this range.
Latest-generation double-conversion systems may use a three level inverter design, which doubles the number of what per phase to allow for lower-voltage rated devices to be used in a series relationship. This helps to raise the efficiency of the inverter by typically 1-3% over two-level inverter designs, therefore reducing the overall cost of operating the UPS. PP 496 Data Center Handbook: 2015, Hwaiyu Geng. Wiley & Sons Inc
This doubles the number of IGBTs per phase to allow for lower-voltage rated devices to be used in a series relationship.
UPS use IGBT transistors in place of what, Allowing the UPS rectifier to be controlled such that its input current is sinusoidal and its input Power Factor near 0.99? Both of these traits allow for easy interface with on-site generators, and they eliminate the large costly “harmonic LC” input filter required for SCR-based designs. PP 496 Data Center Handbook: 2015, Hwaiyu Geng. Wiley & Sons Inc
These use IGBT transistors in place of SCR’s. They are less costly, have a high .99 PF, and it’s input current is sinusoidal.
most basic and typical for a single ups installation is a stand-alone bypass cabinet, typically called a wraparound” PP 497 Data Center Handbook: 2015, Hwaiyu Geng. Wiley & Sons Inc
The most basic and typical for a single UPS installation Maintenance bypass is a stand-alone bypass cabinet which can be completely removed from the load, typically called a__________. Some UPS systems do come with “an internal” maintenance bypass but you need to discuss the capability of this switch the manufacturer to see how much of the ups is serviceable with only this switch installed. PP 496 Data Center Handbook: 2015, Hwaiyu Geng. Wiley & Sons Inc
A “wraparound” maintenance bypass switch is the term given for these systems.
The UPS needs to be put in to what prior to the system being put in the maintenance bypass?
Static Bypass prior to the system being put in the maintenance bypass. Maintenance bypass is usually a wrap around switcheither of rotary or MCB design which allows the UPS to be powered down with the load powered directly from the mains whist maintenance is carried out on the UPS. source: http://www.harlandsimonups.com/reference/faqs/
A UPS in static bypass or manual bypass, the load is being fed by?
Please note that in static bypass or manual bypass the load is being fed by raw mains power and any loss of power during this mode your load will not be protected.
Batteries used to be sized in Ah, they are now sized in?
Watts per cell (WPC). source: http://www.harlandsimonups.com/reference/faqs/
What is the only type of UPS that can supply a different frequency than the default frequency?
An online UPS is the only type of UPS that can do this.
What is the purpose of the DC-to-DC converter? PP 497
the purpose of the DC-to-DC converter is to provide proper battery charging voltage for systems with either a higher or lower DC link “DC Link”
What is a “DC Link”?
A DC link is a connection which connects a rectifier and an inverter. These links are found in converter circuits and in VFD circuits. ��The AC supply of a specific frequency is converted into DC. This DC, in turn, is converted into AC voltage.
The DC link is the connection between these two circuits. The DC link usually has a capacitor known as the DC link Capacitor. This capacitor is connected in parallel between the positive and the negative conductors.
The DC capacitor helps prevent the transients from the load side from going back to the distributor side. It also serves to smoothen the pulses in the rectified DC.
Static bypass switches are typically found in what type of UPS systems?
double-conversion UPS systems, some higher powered single-conversion systems, and rotary systems. PP497 Data Center Handbook: 2015, Hwaiyu Geng. Wiley & Sons Inc.
What is the function of the Static Bypass Switch in a UPS?
The job of this switch in a UPS system is to supply a direct path for the utility mains to connected load equipment. PP497 Data Center Handbook: 2015, Hwaiyu Geng. Wiley & Sons Inc
The job of this switch in a UPS system is to supply a direct path for the utility mains to connected load equipment; however, the mains must be within a certain tolerance range, typically +/- what %.
+/-10% is the tolerance range for mains connected to this. PP497 Data Center Handbook: 2015, Hwaiyu Geng. Wiley & Sons Inc
Static Bypass Switches; there are usually several reasons why the switch is used. What are they?
Maintenance of the UPS
To quickly transfer power to the utility source
to be the main power path for high-efficiency modes in multimode UPS systems. PP 497 Data Center Handbook: 2015, Hwaiyu Geng. Wiley & Sons Inc
When a static bypass switch is used for maintenance of the system, activating the switch to ensure that the utility and UPS output voltages are synchronized so what can be done?
A maintenance bypass breaker can be closed. PP 497 Data Center Handbook: 2015, Hwaiyu Geng. Wiley & Sons Inc
Static switches are built using SCRs, as they are (1-10ms) to close than mechanical-type contractors (50-100ms). They need to be able to close within milliseconds (ms) to make sure the load equipment does not see a large disruption in what? PP497 Data Center Handbook: 2015, Hwaiyu Geng. Wiley & Sons Inc
mains power.
Some UPS designs use both SCRs and a mechanical contractor in parallel, as the SCRs make the quick transition and the contractor closes to provide unlimited bypassing. This type of static bypass is known as what? PP 497 Data Center Handbook: 2015, Hwaiyu Geng. Wiley & Sons Inc.
A “momentary static switch,” and most times, is NOT rated to operate continuously and if it had to operate under full load, it would fail.
Functions and techniques divide industrial timers into how many categories? What are they? NJATC, Motor Controls: timers, 2010 PP 127
Dashpot controlled, synchronous clock, and solid-state.
Which is more accurate a mechanical timing relay or an electronic timing relay? NJATC, Motor Controls: timers, 2010, PP 128
An electronic timing relay is more accurate
The timer functions available from most suppliers include What? NJATC, Motor Controls: timers, 2010, PP 128
On delay, off delay, one-shot, fleeting off delay, repeat cycle (or flasher) are all of these.
The two most common functions used by a timer are what? NJATC, Motor Controls: timers, 2010, PP 128
On delay and off delay are the most common functions used by this.
On delay timers have no, or some, change during the timing with the output contacts.
On delay have no change and start out timing when the contacts are energized. The memory method is ON DELAY=NOTC NCTO, whereas off delay is NOTO and NCTC.
On delay timers are also called what? NJATC, Motor Controls: timers, 2010, PP 129
Delay on energize or DOE. They start timing when energy is applied and change state at the end of timing.
What type of timer is a device with a preset time. That starts after the input signal is removed from electronic timing relay or power is removed from a mechanical timing relay? NJATC, Motor Controls: timers, 2010, PP 129
This describes an OFF DELAY timer.
The timed contacts of the timer immediately change state when the timer is energized or initialized and returned to their original state after the set time delay has elapsed describes what type of timer? NJATC, Motor Controls: timers, 2010, PP130
Off delay timer also known as DODE. Think NO(TO) and NC(TC) where ( ) is the end of timing sequence, meaning the contacts changed when the power was removed from the timer.
Components drawn on motor control drawings are in their what state? NJATC, Motor Controls: timers, 2010, PP 130
These components are in the deenergized or on the shelf state, also called the normal state.
Associate on delay with the delay starting when timers are turned on, or energized. Associate off delay with? NJATC, Motor Controls: timers, 2010, PP 132
when the mechanical timers are turned off or deenergized. Removal of the trigger or power starts the delay time.
The arrow points up or down when depicting on or off delay and how do you remember this? NJATC, Motor Controls: timers, 2010, PP 132
The arrow points up with on delay and down with off delay. This is best remembered by using the analogy of what would stay on or off a shelf. So ^ is staying on the shelf and v is falling off of the shelf.
On delay timers have what type of contacts and what type are associated with off Delay? How can this be remembered? NJATC, Motor Controls: timers, 2010, PP 132
Both start with and NO or NC no letters are repeated in the on delay timer. Answer: ON DELAY- NOTC and NCTO
OFF DELAY- NOTO & NCTC. The letters are repeated in the OFF DELAY timer.
There are two mechanical timers that are used in industrial applications, what are they? NJATC, Motor Controls: timers, 2010, PP 133
The synchronous timer and the dashpot timer are used in these applications. The solid state electronic timer would be sensitive to heat.
A synchronous timer, also referred to as an interval or on/off timer, will alternate energizing and de-energizeing a load at a specific rate. Synchronous timers will energize for the same amount of time that the load will remain de-energized. For mechanical relay applications, the relay contacts will alternate between closed and open. The amount of time the contacts are closed will equal?
the amount of time the contacts are open.
In a Synchronous timer when the triggers are gold or silver pegs inserted on the periphery of the rotating dial this indicates what by color? NJATC, Motor Controls: timers, 2010, PP 133
Gold is the ON time setting and Silver is the OFF time setting.
The Electronic or solid-state time delay timer has a time delay with ranges from what? NJATC, Motor Controls: timers, 2010, PP 135
Fractions of a second to hundreds of minutes, and is considered extremely accurate, describe this type of timer.
Timers with or without external triggers usually have what? NJATC, Motor Controls: timers, 2010, PP 135
Without external triggers these usually have 8 pin bases and with external trigger requirements use an 11 pin configuration.
The term "dry contact" on the external control switch of a non-programmable electronic timer indicates what? NJATC, Motor Controls: timers, 2010, PP 135
The term indicates that the external switch contacts must have low current switching characteristics.
What type of timer rarely has instantaneous contacts? NJATC, Motor Controls: timers, 2010, PP 135
Single function timers rarely have these.
The contacts of solid-state timers have limited current carrying capacity, usually less than how many amps? NJATC, Motor Controls: timers, 2010, PP 135
These contacts on this type of timer usually have less than 10 A current carrying capacity.
While air cooling is the most economical way to cool servers in racks, _______ cooling is the most efficient way to remove heat generated from processors.
Water is the most efficient form of this in data centers.
A data server’s utilization efficiency is estimated to be a disappointing _____?
20%
Based on “Power Usage Effectiveness.” March 2012 prepared by LBNL, _____% of total energy is used in power and cooling a data center and 66.6% by IT load. In a typical server, 30% of power is consumed by a processor and 70% by peripheral equipment that includes power supply, fans, drive, and so on. PP4 Data Center Handbook: 2015, Hwaiyu Geng. Wiley & Sons Inc
33.4% or approximately one third of the power use in a data center is this.
________ is a method of running multiple independent virtual operating systems on a single physical computer. It is a way of allowing the same amount of processing to occur on fewer servers easing server utilization. instead of operating many servers at low CPU utilization, _________ combines the processing power onto fewer servers that operate at higher utilization. Both blanks are the same answer. PP5 Data Center Handbook: 2015, Hwaiyu Geng. Wiley & Sons Inc
Virtualization does this in a data center.
Cloud computing provides various service models including ______,________,&_______. It benefits Data center managers by offering resource pooling and optimizing resource uses with lower costs.
Software as a Service (SaaS), Infrastructure as a Service (IaaS), and Platform as a Service (PaaS) is part of this. PP5
What is an architectural approach that has all ICT (information Control Technology) infrastructure (server, storage, networking, and security virtualized through hardware-independent management system.
Software-Defined Data Center (SDDC) pioneered by VMware, is this.
As the server speeds up, _____ air is delivered, when the server slows down, _____ air is delivered. PP 31
As the server speeds up, more air is delivered, when the server slows down, less air is delivered.
Self-Contained In-Row Cooling come in many varieties such as chilled water-cooled air-cooled DX, low-pressure pumped refrigerant and even CO2 cooled. These are best applied when? 31 Data Center Handbook: 2015, Hwaiyu Geng. Wiley & Sons Inc
These are best applied when there is a grouping of high-density, high heat generating servers that creating difficulties for the balance of the data center.
Once the staple of data centers of yore, sectors like academic research high-performance computing continue to use water-cooled computers and is typically not thought of as an airflow management strategy, but it is. The water cooling keeps the airflow through the computer to a minimum. Components not water-cooled still need airflow for heat dissipation. Typically a water-cooled cabinet will reject _____% of the total cabinet power capacity to the air, a nontrivial number when the IT cabinet houses 50-80 kw computers. PP31 Data Center Handbook: 2015, Hwaiyu Geng. Wiley & Sons Inc
Typically a water-cooled cabinet will reject 10-30% of the total cabinet power capacity to the air
Proper airflow management creates cascading efficiency through many elements in the data center. If done correctly, it can significantly reduce problems related to re-entrainment of hot air into the cold aisle, which is often the culprit of? PP30 Data Center Handbook: 2015, Hwaiyu Geng. Wiley & Sons Inc
re-entrainment of hot air into the cold aisle, is often the culprit of hot and thermal overload.
Immersion cooling is a technique that submerges the servers in a large container of mineral oil. The servers require some modification; but by using this type of strategy _____are eliminated from the computers. The oil is circulated through the container around the servers and is typically pumped to heat exchanger that is tied to outdoor heat rejection equipment. PP32 Data Center Handbook: 2015, Hwaiyu Geng. Wiley & Sons Inc
by using this type of cooling strategy fans are eliminated from the computers.
Delay on Energize (DOE) and Delay On De-energize (DODE) both have what in common?
Both of these timers start out as energized.
What accelerates switch damage? NJATC, Motor Controls: contactors and starters, 2010, PP 86
When switches are opened slowly this occurs.
The standard markings for coils on IEC and NEMA starters is what? NJATC, Motor Controls: contactors and starters, 2010, PP 87
IEC is marked A1 & A2, whereas NEMA is marked without standardization.
IEC starters have what type of reset? NEMA? NJATC, Motor Controls: contactors and starters, 2010, PP 87
IEC starters have Auto reset but no remote reset. NEMA have neither auto or remote resets.
Which starter contacts are easier to change? IEC or NEMA? NJATC, Motor Controls: contactors and starters, 2010, PP 87
NEMA. IEC is too expensive due to labor, thus are recommended to be replaced.
What is the difference between a CONTACTOR and a STARTER? NJATC, Motor Controls: contactors and starters, 2010, PP 89
A CONTACTOR is without overloads, whereas a STARTER has overloads.
When overload protection is included in the load, is it duplicated elsewhere in the branch circuit? NJATC, Motor Controls: contactors and starters, 2010, PP 89
In a branch circuit load, this is not duplicated. The branch circuit is by definition located after the final over current protection device (OCPD).
Contacts are divided into what categories? NJATC, Motor Controls: contactors and starters, 2010, PP 90
Normally open power poles, & normally open or normally closed auxillary contacts are the categories of contacts.
Contactors most often have how many power poles and auxillary contacts? NJATC, Motor Controls: contactors and starters, 2010, PP 90
These normally have 2-3 power poles and 1-8 auxiliary contacts.
Note:Think of single phase which is two incoming conductors and three phase with 3 incoming conductors.
With this you can control a greater number of circuits with a single pilot device. NJATC, Motor Controls: contactors and starters, 2010, PP 90
You need a contactor to do this.
What is the difference between FLA and FLC? NJATC, Motor Controls: contactors and starters, 2010, PP 93
There is no difference between these two terms. FLA is full load amperes and FLC is Full load current.
What carries the motor current, The auxillary contacts or the contactor? NJATC, Motor Controls: contactors and starters, 2010, PP 93
Contactor power poles carry all of the motor current.
What contact is used for electrical hold or start pushbutton sealing requirements in the control circuit? NJATC, Motor Controls: contactors and starters, 2010, PP 93
Normally open auxiliary contacts are used for this purpose. On a nema starter they are contacts 2 & 3.
How do auxiliary contacts function? NJATC, Motor Controls: contactors and starters, 2010, PP 95
This type of contact functions just like a normal relay. When the contractor is actuated normally open contacts close and normally closed contacts open.
What type of auxiliary contact provides a higher degree of reliability than the standard auxiliary contact? NJATC, Motor Controls: contactors and starters, 2010, PP 95
Bifurcated auxiliary contacts provide a higher degree of reliability than the standard auxiliary contacts.
Contactors designed for power control applications other than motors are called what by the Manufacturer? NJATC, Motor Controls: contactors and starters, 2010, PP 95
Definite purpose or special use contactors are used for this type of application.
What is the most common definite use contactor application? NJATC, Motor Controls: contactors and starters, 2010, PP 95
lighting contactors fit this description.
The coil of the contactor is controlled by what? NJATC, Motor Controls: contactors and starters, 2010, PP 97
This is controlled by automatic or manual pilot devices.
The most common pilot devices for lighting are what? NJATC, Motor Controls: contactors and starters, 2010, PP 97
Timeclocks, photocells or manual switches are considered these.
Lighting contactor control transformers have what range? NJATC, Motor Controls: contactors and starters, 2010, PP 97
45 to 250 VA
Toggle switches are usually found on what type of manual motor starter? Where as built in pushbuttons are used on what? NJATC, Motor Controls: contactors and starters, 2010, PP 101
Integral Motors are for how many horsepower?
Toggle switches are usually found on fractional horsepower manual motor starters, and built in pushbuttons are usually found on integral horsepower manual motors starters.
More than one HP. Per the definition of integer: mathematics : any number that is not a fraction or decimal : any whole number or its negative.
In a ladder diagram, from left to right are components shown in order of importance. T or F?
True. Second Edition Electricians Guide to Motor Controls; Richard Cox. PP 75
Do contacts associated with relays, timers, motor starter, and the like always have the same number or letter designation as the device that controls them?
Yes. Second Edition Electricians Guide to Motor Controls; Richard Cox. PP 75
In a ladder diagram, devices that perform a stop function are normally wired in what way?
In series. Second Edition Electricians Guide to Motor Controls; Richard Cox. PP 76
When devices are wired in series in a ladder diagram, the are said to have what relationship?
An AND relationship. For example, both switch a and b must be closed for the motor to start. Second Edition Electricians Guide to Motor Controls; Richard Cox. PP 76
Devices in a ladder diagram that perform a start function are normally wired in what way?
parallel. Second Edition Electricians Guide to Motor Controls; Richard Cox. PP 76
When switches and devices are wired in parallel they are said to have what relationship?
An OR relationship. Second Edition Electricians Guide to Motor Controls; Richard Cox. PP 77
What method of checking fuses of motors and motor control circuits is preferred because more often than not, more than one fuse will be blown in a 3 phase circuit.
The criss cross method. Second Edition Electricians Guide to Motor Controls; Richard Cox. PP 79
What type of wire control is called low voltage or no voltage release?
two wire control. Second Edition Electricians Guide to Motor Controls; Richard Cox. PP 85
What type of wire control is called low voltage or no voltage protection?
3 wire control. Second Edition Electricians Guide to Motor Controls; Richard Cox. PP 85
On the NEMA starter, termination points 2 and 3 are referred to as what?
Holding contacts. Second Edition Electricians Guide to Motor Controls; Richard Cox. PP 86
The difference between low voltage release (lvr) and low voltage protection (lvp) is what regarding operation of the starter?
Whether the starter will restart automatically. Second Edition Electricians Guide to Motor Controls; Richard Cox. PP 91
Controllers for industrial motors can be grouped into what broad categories?
Controllers can be grouped into 3 broad categories. Second Edition Electricians Guide to Motor Controls; Richard Cox. PP 53
Manual starters
Contactors
Magnetic Starters
Manual starters are usually limited to what HP or less for motors?
10hp or less. Second Edition Electricians Guide to Motor Controls; Richard Cox. PP 53
If a general use switch is used on a 2hp or less and 300 volts or less motor, what is its ampere rating?
Not less than twice the FLC rating of the motor. Second Edition Electricians Guide to Motor Controls; Richard Cox. PP 53
Define a harmonic. NJATC, Transformers 2006, PP 99
A harmonic is a voltage or current at a frequency that is an integer whole number multiple (second, third, fourth,) etc. of the fundamental frequency.
What causes harmonics? NJATC, Transformers 2006, PP 99
Harmonics are caused by nonlinear loads that draw current in pulses, for only a portion of the cycle, resulting in a distorted waveform.
What can be used to measure the amount of voltage and current harmonics on a line? NJATC, Transformers 2006, PP 100
The power quality meter.
Odd-numbered harmonics add to each other or cancel each other out? NJATC, Transformers 2006, PP 101
Odd-numbered harmonics add together and increase their effect.
Odd-numbered harmonics do what regarding resistance and eddy currents? PP 101
Odd numbered harmonics have increased resistance losses and eddy current losses in transformers.
Even-numbered harmonics are generally what size and why? NJATC, Transformers 2006, PP 101
Even-numbered harmonics are generally fairly small because the tend to cancel each other out.
Even-numbered harmonics usually indicate what may be present in the transformer secondary winding and caused by what? NJATC, Transformers 2006, PP 101
Even-numbered harmonics usually indicate that a DC current may be present in the transformer secondary winding. The DC offset is typically caused by half wave rectification due to a failed rectifier.
A DC offset can cause a transformer to become what? NJATC, Transformers 2006, PP 101
A DC offset can cause a transformer to become saturated on alternate half-cycles and draw extremely high currents that can burn out the primary. Remember: a DC offset is caused by failed rectification due to a failed rectifier.
What is this symptom of a DC offset? NJATC, Transformers 2006, PP 101
These problems may be noticeable as a strong vibration and a very loud noise coming from the transformer core.
A DC offset equaling more than how much of a percent of the rated current can cause problems? NJATC, Transformers 2006, PP 101
1 percent.
What are Triplen harmonics? What type of loads draw these type of harmonics? NJATC, Transformers 2006, PP 101
Triplen harmonics are on multiples of the third harmonic 3rd, 9th, 15th etc. Only single phase loads generate triplen harmonics.
Which harmonic can cause problems such as overloading neutral conductors, telephone interference, and transformer overheating? NJATC, Transformers 2006, PP 101
Triplen harmonics.
Which harmonic is the only harmonic that contributes to the problem of high neutral currents? NJATC, Transformers 2006, PP 101
Only the triplen harmonics contribute to the problem of high neutral currents. Because of their lower current levels and higher frequencies, The ninth, 15th, and higher triplen harmonics generally distort the neutral current only slightly, and often do not have a significant effect on actual RMS neutral current.
Phaseor rotation is the order in which waveforms from each phase (A, B, and C) cross zero.
What is harmonic sequence? NJATC, Transformers 2006, PP 101
Harmonic sequence is the phasor rotation with respect to the fundamental 60 Hz frequency.
Why is phase sequence of a Harmonic important? NJATC, Transformers 2006, PP 101
The sequence of a harmonic is important because it determines the affects a harmonic has on the operation of loads and components such as conductors within a power distribution system.
Positive sequence harmonics are what? name the numbers. NJATC, Transformers 2006, PP 101
First, fourth, seventh, etc.
Positive sequence harmonics have what phase sequence NJATC, Transformers 2006, PP 101
Positive sequence harmonics have the same phase sequence as the fundamental harmonic.
Positive sequence harmonic rotates in what direction in regards to the fundamental in an induction motor? NJATC, Transformers 2006, PP 101
Positive sequence harmonics rotate in the same direction as the fundamental in an induction motor.
What is the numeric sequence of negative harmonics? NJATC, Transformers 2006, PP 102
Second, fifth, eighth, etc.
A negative sequence harmonic rotate in what direction from the fundamental in an induction motor? NJATC, Transformers 2006, PP 103
A negative sequence harmonic rotates in the opposite direction from the fundamental and induction motor.
Does a negative sequence harmonic reduce the forward torque of a motor? NJATC, Transformers 2006, PP 103
Yes.
What is the numerical order of zero sequence harmonics? NJATC, Transformers 2006, PP 103
Third, sixth, ninth, etc.
Zero sequence harmonics cannot cancel but can add together where? NJATC, Transformers 2006, PP 103
What are significant contributors to current on neutral wires? NJATC, Transformers 2006, PP 103
Zero sequence harmonics do not cancel each other, but can add together in the nuetral conductor of three phase, 4-wire systems.
Single phase devices with rectifier power supplies, such as fluorescent lighting with electronic ballasts, computers, copiers, and other similar electronic devices, are significant contributors to current on neutral wires.
Define total harmonic distortion. NJATC, Transformers 2006, PP 103
Total harmonic distortion is the amount of harmonics on A line compared to the fundamental frequency of 60 Hz.
Total Harmonic distortion (THD) is what? ATP & NJATC, Transformer Principles & Applications, 2006: Chapter 5-Harmonics, PP 10 (NC set 2)
What is the amount of harmonics on aline compared to the fundamental frequency of 60 Hz.
Voltage THD (total harmonic distortion) is caused by what? ATP & NJATC, Transformer Principles & Applications, 2006: Chapter 5-Harmonics PP 103 (NC set 2)
Harmonic currents on the line create this.
High-voltage distortion is a problem because of what? ATP & NJATC, Transformer Principles & Applications, 2006: Chapter 5-Harmonics PP 103 (NC set 2)
Because voltage distortion becomes a carrier for harmonics to Linear loads such as motors.
For best results, the voltage and current THD (total harmonic distortion) should not exceed what percent of the fundamental frequency? ATP & NJATC, Transformer Principles & Applications, 2006: Chapter 5-Harmonics PP 103 (NC set 2)
Voltage THD 5%
Current THD 20%
Where should THD (total harmonic distortion) be measured at? ATP & NJATC, Transformer Principles & Applications, 2006: Chapter 5-Harmonics PP 103 (NC set 2)
THD should be measured at the transformer.
TDD, total demand distortion is what ratio? ATP & NJATC, Transformer Principles & Applications, 2006: Chapter 5-Harmonics PP 103 (NC set 2)
TDD is the ratio of the current harmonics to the maximum load current.
How is TDD (total demand distortion) and THD (total harmonic distortion) different? ATP & NJATC, Transformer Principles & Application, 2006: Chapter 5-Harmonics PP 103 (NC set 2)
TDD is referenced to the maximum current measurement taken over time.
Any AC circuit consists of what four elements of power? ATP & NJATC, Transformer Principles & Application, 2006: Chapter 5-Harmonics PP 105 (NC set 2)
Real, reactive, harmonic, and apparent.
What shows up as a phase displacement between the current and voltage waveforms? ATP & NJATC, Transformer Principles & Application, 2006: Chapter 5-Harmonics PP 105 (NC set 2)
Reactive power.
Apparent power is the power, and VA or kVA and is the sum of what? ATP & NJATC, Transformer Principles & Application, 2006: Chapter 5-Harmonics PP 105 (NC set 2)
Apparent power is the sum of true power, reactive power, and harmonic power.
Displacement power factor is what? ATP & NJATC, Transformer Principles & Application, 2006: Chapter 5-Harmonics PP 105 (NC set 2)
The ratio of true power to apparent power due to the phase displacement between the current and voltage.
What can usually be added to a circuit to correct displacement power factor? ATP & NJATC, Transformer Principles & Application, 2006: Chapter 5-Harmonics PP 105 (NC set 2)
Capacitors can usually be added to the circuit or distribution system to correct this.
What is the formula for displacement power factor? ATP & NJATC, Transformer Principles & Application, 2006: Chapter 5-Harmonics PP 105 (NC set 2)
It is the same as the standard power factor formula, and is due to the phase displacement between the current and voltage.
What is displacement power factor? ATP & NJATC, Transformer Principles & Application, 2006: Chapter 5-Harmonics PP 105 (NC set 2)
The ratio of true power to apparent power due to THD.
What cannot be added to a circuit or distortion system to compensate for distortion power factor? ATP & NJATC, Transformer Principles & Application, 2006: Chapter 5-Harmonics PP 105 (NC set 2)
Capacitors cannot be added to correct this.
Distortion power factor is calculated by what formula? ATP & NJATC, Transformer Principles & Application, 2006: Chapter 5-Harmonics PP 105
Total power factor is the product of what? ATP & NJATC, Transformer Principles & Application, 2006: Chapter 5-Harmonics PP 105 (NC set 2)
What may cause reset and loss of data in computer systems? ATP & NJATC, Transformer Principles & Application, 2006: Chapter 5-Harmonics PP105 (NC set 2)
Sags and swells may cause this because of insufficient peak voltage to keep the capacitor charged in an SMPS.
It is important to know power factor because it relates to apparent power which is used to size what? ATP & NJATC, Transformer Principles & Application, 2006: Chapter 5-Harmonics PP 106 (NC set 2)
The elements of a power distribution system is sized by this.
What is current crest factor? ATP & NJATC, Transformer Principles & Application, 2006: Chapter 5-Harmonics PP 106 (NC set 2)
The peak value of waveform divided by the RMS value of the waveform.
The UPS can supply what crest factor at full load? how does this relate to lower loads? ATP & NJATC, Transformer Principles & Application, 2006: Chapter 5-Harmonics PP 107 (NC set 2)
UPS has a crest factor of three at full load, but can supply a higher crest factors at lower loads.
A smoothing capacitor has an extended charge time that has what effect on the crest factor? ATP & NJATC, Transformer Principles & Application, 2006: Chapter 5-Harmonics PP 107 (NC set 2)
This reduces the crest factor.
Harmonic distortion is created by computers, printers, electronic ballasts, and name two more. ATP & NJATC, Transformer Principles & Application, 2006: Chapter 5-Harmonics PP 107 (NC set 2)
Variable speed motor drives and medical test equipment.
A switch mode power supply is a power supply for electronic devices that does what? ATP & NJATC, Transformer Principles & Application, 2006: Chapter 5-Harmonics PP 107 (NC set 2)
Quickly switches the load current on and off in order to deliver a stable output voltage.
A typical single phase SMPS is designed to use what immediately after the AC power supply? ATP & NJATC, Transformer Principles & Application, 2006: Chapter 5-Harmonics PP 108 (NC set 2)
A full wave bridge rectifier.
With a smoothing capacitor, current flows during what part of the cycle? ATP & NJATC, Transformer Principles & Application, 2006: Chapter 5-Harmonics PP 108 (NC set 2)
Where the voltage exceeds the minimum value, this occurs with a smoothing capacitor.
Flat-topping occurs when? ATP & NJATC, Transformer Principles & Application, 2006: Chapter 5-Harmonics PP 108 (NC set 2)
When many loads draw current in pulses at the maximum voltage level and overload the power source, this occurs.
Why are loads characterized as nonlinear? ATP & NJATC, Transformer Principles & Application, 2006: Chapter 5-Harmonics PP 108 (NC set 2)
When the input current is significantly distorted as compared to the ideal current waveforms.
When the conductor is straight, the flux lines cut through only one of the conductors, but when the conductor is ______ the flux lines cut through inductor at more than one point. This increases the CEMF by self induction.
Coiled. When the conductor is coiled it allows more points at which the lines of flux can cross the conductor and increase this.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP76
Because an iron core provides an easy path for magnetic flux, windings ______ cores produce greater self-inductance windings with an air core.
with soft iron windings produce this.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation
, based on the 2014 PP76
Longer cores result in? And what happens when core length is doubled?
fewer flux lines are the result of this.
This results in reduced inductance. If the core length is doubled, the CEMF decreases by 50%.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP76
When the applied voltage is at its maximum in one direction, the induced voltage is at its maximum in what way?
This is at its maximum in the opposite direction.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP77
An electrical source with many motors and inductive loads tends to have a high amount of inductive reactance and a low power factor.
Adding capacitors will help counteract high inductance and increase the power factor. This will help with the problem of this type of load.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP77
Circuits and equipment must be sized to the circuit ____(I2R, E2/R, or IxE)____ loads?
VA is what this must be sized to. Or apparent power and expressed by IxE. In a DC circuit, however it is IxExPF in an AC single phase circuit and IxEx1.73 (√3) in a 3 phase AC circuit.
If you measure voltage and current in an inductive or capacitive circuit and multiply them together, the product is the apparent power supplied to the circuit by the source.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation
, based on the 2014 PP79
To determine the true power, or watts, consumed by a DC versus AC circuit, what formula must be used? This is not apparent power.
DC power= IxE
AC power(watts)= IxExPF (PF=R/Z or True power/ apparent power (I2R/IE).
These two formulas determine this type of power consumed by the circuit. It is important to note the watt loss or I2R is not used.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP79
Alternating-current inductive or capacitive reactive loads cause the voltage and current sine waves to be out-of-phase with each other. power factor measures what in regards to the wave form?
This measures how far the current waveform is out-of-phase the voltage waveform.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP80
What condition is called “unity power factor” in a purely resistive circuit?
Unity power factor is when the power factor is at 100% in a this type of circuit.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP79
Why are circuits and equipment sized per the VA available to the load?
Apparent power (VA) is used for sizing circuits and equipment. Because the VA of the load isgreater than the watts of the load, fewer loads can be supplied by each branch circuit. More circuits and panels, and larger transformers may be required. This is why these are sized per this.
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP82
Transformers are always sized based on what rating?
What is the formula for this?
KVA (apparent power) is always the rating for these, not KW because they are an inductive load which results in apparent power. Apparent power is measured in kVA, while KW is used only for true power such as resistive loads.
Apparent power = KW/PF so…
kVA= IxE/1000 for KVA would not account for power factor and would be wrong as mentioned on page 19 of Master Electrician: 2014 Exam Questions & Study Guide. Ray Holder
Mike Holt’s Illustrated Guide to Electrical Exam Preparation, based on the 2014 PP82
The formula for I or current in a 3 phase circuit is what?
The formula for I in a 1 phase circuit when watts and volts are known, and therefore current, true power and apparent power by default.
I=P/E x 1.732 (3 phase)
I=P/E x PF (single phase)
Master Electrician: 2014 Exam Questions & Study Guide. Ray Holder
The formula for I using P and E known values is? This is used in a single phase circuit. Or what in DC.
This =P/ExPF. In DC or a purely resistive circuit it would be P/E=I
The short circuit calculation for a 3 phase and single phase circuit is what?
short circuit current is calculated by the formula
3 phase: KVA x 10000
E LtoL x 1.732
1 phase is just E
Eventually DC power distribution will be found only in what places? NJATC, AC Theory, PP 256 (NC set: Generators)
This type of power will be eventually found where extremely high torque per HP is required or where the nature of the work required DC, such as in electrolysis applications.
The left hand rule and right hand rule are used for what type of electron theory respectively? NJATC, AC Theory, (NC set: Generators) PP 13
Right-hand rule: conventional flow +to-
Left-hand rule: Electron Current Flow -to+ (Flemming's left hand rule for generators; motion, electro-magnetic lines of force, current flow.
As the armarture rotates it begins to cut the maximum lines of flux when? NJATC, AC Theory, (NC set: Generators) PP 259
This cuts the maximum lines of flux when 90 degrees or perpendicular to the magnetic field.
What is key to determining wether the output voltage of the generator is alternating or direct? NJATC, AC Theory, PP 260 (NC set: Generators)
The method of removing the voltage from the armature determines this. In AC the armature may or may not be rotating.
The output voltage from the brushes in a generator (DC) will always be what? NJATC, AC Theory, PP 260 (NC set: Generators)
This output voltage will always be a pulsating DC going form zero voltage to peak voltage but never reversing.
What will allow the voltage to remain positive even though the armature is producing an alternating voltage? NJATC, AC Theory, PP 261 (NC set: Generators)
The change in commutator segments allows this.
The rotating member of the DC generator is what? NJATC, AC Theory, PP 262 (NC set: Generators)
Armature, in a DC generator. The method of removing the voltage in the armature is key to determining wether the output voltage of the generator is DC or AC. Consisting of the iron core, commutator, and the windings.
In a DC generator, the armature assembly has how many parts and what are they? NJATC, AC Theory, PP 262 (NC set: Generators)
laminated iron core, commutator and windings,
coils or windings (3 types), and shaft comprise this.
The armature windings come in three basic types which are? Define which ones have additive current, Additive voltage, and additive current and voltage. NJATC, AC Theory, PP 262 (NC set: Generators)
Lap -parallel-Additive I
Wave -Series-Additive E
Frog-leg -Series parallel-Additive I & E
Are three basic types of this?
Which is the most common armature winding configuration? NJATC, AC Theory, PP 263 (NC set: Generators)
frog-leg = series parallel is this.
The field winding is connected to what type source of power? NJATC, AC Theory, PP 264 (NC set: Generators)
DC is the type of power source that this is connected to in a generator. Field winding definition: The part of the DC generator that creates the magnetic field that is cut by the armature windings.
There are two types of field windings in a DC generator... what are they? NJATC, AC Theory, PP 264 (NC set: Generators)
Field windings are marked as what?
Shunt and series
Series marked S1 & S2
Parallel marked as F1 & F2
Explain the output voltage to the load current relationship of shunt and series field windings? NJATC, AC Theory, PP 264 (NC set: Generators)
Shunt= E output lowers/ I Load raises- inversely proportional
Series= E output raises / I Load raises Directly proportional
The series generator stator field winding type must be what? NJATC, AC Theory, PP 265 (NC set: Generators)
This generator stator field winding wiring type must be self excited, meaning the pole pieces must have some sort of residual magnetism to start producing a voltage in the armature.
Because of the varying voltage, the series generator field winding wiring type is best suited for what type of load? NJATC, AC Theory, PP 266 (NC set: Generators)
constant loads are best suited for this type of generator field winding type and for this reason.
What does the shunt generator provide before the load is applied? NJATC, AC Theory, PP 266 (NC set: Generators)
The full voltage is applied before this in a shunt generator.
Define a field winding. NJATC, AC Theory, PP 264 (NC set: Generators)
The part of the DC generator that creates the magnetic field that is cut by the armature windings.
Define an armature. NJATC, AC Theory, PP 341 (NC set: Generators)
The component in the process of generation that has voltage induced into it. It is not always the moving component but is the place where generated voltage is collected.
The amount of voltage generated by a series generator is dependent on what? NJATC, AC Theory 2009, PP 265 (NC set: Generators)
The strength of the magnetic field produced by the pole pieces, turns of wire on the armature, and the speed of rotation of the armature all determine this in a DC generator.
As the load increases on a shunt generator, what happens to the output voltage? NJATC, AC Theory 2009, PP 266 (NC set: Generators)
The output voltage will decrease in this type generator as the load increases.
Another term for a series variable resistor is what? NJATC, AC Theory 2009, PP 266 (NC set: Generators)
Rheostat.
The motor overload relays are for what type of protection of the motor? NJATC, Code Calculations, NJATC, Code Calculations: 2008, PP 120
running protection is the type of protection provided by this in a motor.
What type of motors use the nameplate rating FLC (full load current)? NJATC, Code Calculations, PP 121
What RPM limit defines a low speed motor?
Torque & multi-speed motors used this rating.
less than 1200 RPM defines this motor.
According to section 430.6(B) of the NEC, as applied to torque motors, the FLC (full load current) is what? Taken from where? NJATC, Code Calculations, PP 121
locked rotor current is the FLC of this type of motor. Taken from the nameplate.
Because a multi-speed motor has 2 windings, any one winding is used at any one time, so the multi-speed motor branch circuit is rated at what percentage and why? NJATC, Code Calculations, PP 121
125 percent, is the branch circuit rating in this type of motor, because it is a continuous load.
A multi-speed motor has how many windings? NJATC, Code Calculations, PP 123
Because of this, any one winding is used at any one time, so the multi-speed motor branch circuit is rated at what percentage and why?
2 windings are found in this type of motor.
at 125% because it becomes a continuous load
Periodic duty motors use what to calculate FLC? NJATC, Code Calculations, PP 125
T430.22E (Duty cycle) is used with this type of motor.
Locked rotor current is used in conjunction with what type of motor? NJATC, Code Calculations: 2008, PP126
torque
As it applies to a torque motor, what happens to prevent damage once the motor has, for example, closed a valve? NJATC, Code Calculations: 2008, PP 126
The circuit is opened by means of a torque or limit switch before the locked-rotor current can damage the motor. NJATC, Code Calculations: 2008, PP 126
Wye start, delta-run motors are used for what? NJATC, Code Calculations: 2008, PP 127
This permits how many conductors between the controller and the motor of the wye-start winding and at what calculation % of FLC? NJATC, Code Calculations: 2008, PP 127
At what % rating for line conductors to the controller?
reduced-voltage starting, resulting in a lower starting current.
6 72% for the 2011 NEC
125%
How many sets of conductors are there to calculate for the branch circuit conductors of a wound-rotor motor? NJATC, Code Calculations: 2008, PP 130
There are two sets of conductors to calculate for the branch-circuit conductors of this type of motor: The primary branch circuit conductors to the stator and the secondary conductors connected to the rotor through a bank of resistors.
there are (are not) line electrical connections to the secondary or rotor of a squirrel cage induction motor? pp 130
this motor is also known as what?
are not
Wound-rotor induction motor
When calculating branch circuit ratings of more than one motor per 430.24 of the NEC, on one branch circuit, what is the % of the FLC used? pp 133
Is the largest FLC always the largest HP rating?
125% of the largest FLC and 100% of all others.
No
The purpose of motor branch-circuit short circuit and ground-fault protection is to protect what? NJATC, Code Calculations, pp140 (NC: motor branch circuits)
the circuit conductors, motors, and motor-controller equipment against overcurrent due to short circuits and ground faults.
A more common term for inverse time circuit breaker is what? NJATC, Code Calculations: 2008, PP 141
Thermal magnetic circuit breaker is another term for this.
Is the use of nonstandard rated fuses or circuit breakers permitted for overcurrent and short circuit protection? NJATC, Code Calculations: 2008, PP 141
This is allowed to be used for overcurrent and short circuit protection with a motor.
Motor branch circuit short circuit and GFP uses what 3 types of fuses? NJATC, Code Calculations: 2008, PP 140
non-time delay
time delay
Class CC
Motor GFP and short circuit protection use what 3 types of circuit breakers? NJATC, Code Calculations: 2008, PP 140
the calculations differ only when what type is used?
fixed or inverse time
adjutable trip circuit breakers
instantaneous trip circuit breakers
instantaneous trip CB's
For motor branch circuit ratings on short-circuit and ground fault protection the nameplate is (is not) used for FLC (full load current) rating? NJATC, Code Calculations: 2008, PP 141
This is not used for short-circuit and ground fault protetion for motor FLC?
Starting current is a.k.a.? NJATC, Code Calculations: 2008, PP 141
locked rotor current (LRC) is also known as this.
Where the maximum branch circuit and ground fault protection ratings are shown in the manufactures overload relay table for use with a motor controller or otherwise marked on the equipment, What must be done? NJATC, Code Calculations: 2008, PP 143
The calculated standard size must not exceed the listed manufacturers rating when this occurs with a motor.
A general rule of thumb puts the locked-rotor current for other than a Design B energy-efficient motor at ________ times the motor full-load current. NJATC, Code Calculations: 2008, PP 141
And for Design B?
6 times locked rotor current.
8 or more for the second type.
When sizing a breaker or fuse to motor short-circuit or GFP protection versus overload protection, what is considered the best installation? NJATC, Code Calculations: 2008, PP 146
sizing the breaker or fuse to just protecting the equipment is considered the best installation. I.E. not rounding up.
For torque motors the conductor size is based on what? NJATC, Code Calculations: 2008, PP 158
That name plate full load current of the motor is used for branch circuit calculations with this type of motor, which is the lock rotor current of the motor.
Instantaneous trip circuit breakers are covered separately in 430.52(c)(3) of the NEC and can be set to trip at what range? NJATC, Code Calculations: 2008, PP 153
What does this mean for rounding?
any range within its rating may be used for this type of circuit breaker
no rounding is necessary, for this type of circuit breaker as well.
A service factor on a motor nameplate is 1.15, meaning what? NJATC, Code Calculations: 2008, PP 160
This means that the motor is designed to operate at 115% of FLC without damage.
Motor overload protection requires the use of what to determine FLC? NJATC, Code Calculations: 2008, PP 160
If this is not available then what must be done in what two seperate cases?
nameplate FLC is used for this calculation.
Overload protection should be reduced to 115% when there is no nameplate FLC, and also when a temperature rise greater than 40 celcius / 104 F is present.
Are the overload calculations the same for design B, C, and D motors? NJATC, Code Calculations: 2008, PP 160
The overload calculations are the same for these design motors.
Selecting the higher class overload relay may preclude the need for selecting a higher trip current for what reason? And what are the classes of overload relays? NJATC, Code Calculations: 2008, PP 162
There are three classes of overload relays: Class 10, class 20, and class 30. A class 20 overload will carry the same starting current As a class 10 for a longer period of time. A class 30 will carry the same starting current for a longer period of time than a class 20.
How many amperes does a 40 Hp three phase 480 volt Induction-Type motor draw (assuming an 80% power factor)? What would you need to know about table 430.250 to get this question right?
You would need to know that at the bottom of table 430.250 there is a fine print note: *For 90 and 80 percent power factor, the figures shall be multiplied by 1.1 and 1.25 respectively.
A 300 Hp, 480-volt 451 ampere, 3 phase motor is fed with 1 raceway, if the six paralleled type USE insulated conductors with 75°C terminations de-rated at 80% are used, at least________AWG sized wires are needed for the ungrounded (hot) conductors. (The 90° column can be used if the derating adjustment factors were used). There are two key elements to solving this and they are?
First this allows the 90 degree column to be used if derating adjustment factors were used, or Load/Load correction factor… or, 451/.80=563amps. Secondly 563/2=281amps for parallel raceways.
Control transformers are often referred to as what? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 183
Power supplies
Control transformers are used to provide what sort of voltage power to control systems and devices? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 183
Low-voltage power.
What transformers are used to measure high voltage present on power lines? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 183
Potential transformers.
The most common control transformers have how many primary coils and secondary? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers PP 183
There are two primary coils and one secondary coil on this type transformer.
When the control transformer has the two primary coils wired in parallel what happens? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 183
The voltage is stepped down from 240 V to 24 V. Primary: parallel is 240V and series is 480V.
Control transformer sizes typically range in what VA range? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 184
50 VA 23 KVA is the size range for these transformers.
The size of the control transformer can be determined by what method? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 185
By adding the power requirements of the components in the control circuit you can sizing the transformers.
When does the voltage output of the control transformer decrease? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 185
With an undersized control transformer the total load connected to a control transformer exceeds the rating of the transformer, this happens.
An undersized control transformer can make it difficult to troubleshoot the circuit. Give examples of how. ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 185
What are the two power ratings for a relay, contractor, or starter? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 185
For example, a relay, contactor, or starter has two power ratings: one for holding in the armature and one for pulling in the armature, therefore a starter, relay, or contacted cannot complete the circuit, but can be done so manually.
A lower rating which is the hold-in VA rating, and a higher rating which is the pull-in VA rating.
What NEC section list requirements for transformers used motor control circuits? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 187
430.72C
NEC section 430.72C says that control transformers which occur in the primary winding of less than _____ shall be protected by overcurrent devices 500% or less of the rated primary current. ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 187
Two Amps
What is common industry practice in regards to protection of the control transformer? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 187
It is common industry practice protect this type of transformer on both the primary and secondary side.
A grounded system in regards to a control transformer is what? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 188
A control system with a grounded secondary in the control transformer, making it easy to test voltage to ground on the output side.
A floating system is what? And what cannot be done when troubleshooting this type of control transformer? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 188
A control system without a grounded secondary in the control transformer, which means a voltmeter cannot be used to troubleshoot the circuit by measuring voltage to ground, but relative to the transformer instead.
A circuit that has more than one point connected to earth ground, with a voltage potential difference between the two ground points is what? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 189
What type of transformer can prevent ground loops?
A ground loop.
An isolation transformer.
What safety precautions are taken for heater controls? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 190
Heater controls are usually designed to be normally open and only operate when needed.
What type of transformer is a transformer used to supply low-voltage to power circuits, such as for doorbells, annunciators, and similar systems. ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 190
Bell transformers.
Bell transformers operate like a standard step down control transformer. They usually have an insulated panel with four screws for connections. Describe the configuration of the screws for voltage connections. ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 190
One of the screws is the common and the other three are taps that allow different voltages to be taken off the coil. These taps are usually 6V, 12V, 16V, and sometimes 24V.
What is a precision two winding transformer used to step down high-voltage to allow safe voltage measurement? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 190
A potential transformer.
Although potential transformers are usually fairly small, they're used to measure very high voltages but are typically rated at what VA? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 191
These transformers are typically rated at 500 VA or less.
A transformer correction factor is what? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 192
A number provided by the manufacturer that is used as a multiplier to correct for inaccuracies. The correction factor correct for effects of magnetizing current or internal phase shift created by the internal inductance of the transformer.
Current transformers are unique for what reason? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 193
Because these usually have only one winding they are unique. The primary is connected in series with the line load.
When the primary on a current transformer has a large current rating what may be done with the primary winding? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 193
The primary winding may consist of a straight conductor passing through the center of the magnetic circuit. This straight conductor represents a one turn winding.
The secondary over current transformer must never be allowed to do what? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 194
Why?
Therefore, a current transformer should always have what done to the secondary when not connected to an external load?
This must never be allowed to be open when the primary circuit is energized.
When the circuit is operational, the load on the secondary keeps the magnetizing currents low, keeping turn to turn potential low.
The secondary should be shorted when not connected to an external load.
Three types of current transformers in general use are what? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 195
Window, bar, and wound.
A transformer that consists of a secondary winding wrapped around a core and a primary sent through the opening in the core. ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 195
Window current transformer.
In a window transformer what is passed through the window and acts as the primary? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 195
A power line Is passed through the window and acts as a primary.
A special type of window current transformer with a solid bar placed permanently through the window is what? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 195
A Bar current transformer.
A Bar current transformer is found in installations where the potential is what KV or less? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 195
These transformers are found in installations 25KV or less.
A transformer with separate primary and secondary windings wrapped around a laminated core. ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 195
What is the current transformer.
This type of current transformer is found in the high-voltage side of substations and has a primary conductor the carries the current and a low turn secondary for the output current. ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 195
Wound current transformer.
The secondary of a current transformer is always rated at what amperage? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 197
At 5 amps on the secondary regardless of the current rating of the primary.
Common applications of current transformers include what? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 197
Power metering, motor current monitoring, and variable speed drive monitoring are common applications for this type of transformer.
In power metering a current transformer provides what in comparison to a potential transformer? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 197
The current transformer provides a way to measure the current, and a potential transformer provides way to measure the voltage in this type of metering.
What has current transformers on the lines to the starter to monitor the motor currents? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 197
Motor starters have these type of transformers on the lines.
What is used to transfer the load in the event of a power failure? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 193
Voltage relays.
What is part of instantaneous electronic trip IET circuit that takes the drive off-line if a sudden rise in current occurs that exceeds the rating of the drive? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 197
Variable speed drive current transformers that monitor the incoming current is part of this.
A variable transformer is a transformer used to make fine adjustments to the output voltage. A typical variable transformer can be adjusted from what percentage of the input voltage? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 198
This transformer can be adjusted from 0% to about 170% of the input voltage.
What type of transformer is usually wired is an autotransformer with no electrical isolation between the source and the output? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 198
Variable transformers are usually wired this way.
A typical variable transformer consists of what? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 19
This consists of a copper winding on a toroidal core.
What type of power loss & inefficiencies does a variable transformer usually have? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 198
These transformers can have extremely low power losses with efficiencies as high as about 98%.
An application of variable transformers is what? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 200
Other applications of variable transformers include?
Voltage regulation is an application of this type of transformer.
Temperature control, control lighting, and laboratory equipment testing for over-voltage and under-voltage conditions, are other applications of this type of transformer.
What is used to adjust location of the output tap from the variable transformer? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 200
A stepper motor is used for this.
What can be used with buck boost transformers to create a voltage regulation system? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 200
Variable transformers can be used with this.
An application of variable transformers is what ? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 200
As a voltage regulator is an application of this type of transformer.
The two most common control transformer secondary voltages are what? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 201
24V and 120V are the two most common secondary voltages with this type of transformer.
The secondary output of potential transformers is? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 201
120 V is the secondary output of this transformer.
A current transformer is used to do what? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 201
This transformer is used to step down a high current to make it easier to measure.
What transformers are used together to measure the power delivered to the customer from the utility? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 201
Current and Potential transformers.
A variable transformer uses what that rotates across the winding to provide any desired output voltage within the design range? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 201
A wiper or brush is used to provide any desired output voltage within the design range.
A current transformer is used to step down the line current to make it easier to measure, thus creating what type of voltage transformer? ATP & NJATC, Transformers principles & applications, 2006; Chapter 10: special transformers, PP 193
A modified step-up voltage transformer. Since the power on the primary and secondary of a transformer is the same.
An auto transformer has how much loss compared to a two coil transformer?
Can an auto transformer be used for lighting ballasts?
less loss is in an autotransformer than in a standard two coil transformer. Tom Henry 2011 Journeyman Exam Questions and Answers. PP23
Yes, this can be used for lighting ballasts.
What can be used for starting compensators for AC motors?
An autotransformer. Tom Henry 2011 Journeyman Exam Questions and Answers. PP23
where conductors carry alternate current and are installed in metal enclosures or metal raceways, they shall be so arranged as to avoid heating the surrounding metal by induction, to accomplish this _______ shall be grouped together. Source: Journeyman electrician exam questions and answers, Tom Henry, 2011; PP 26
A. all phase conductors
B. where used, the neutral
C. all equipment grounding conductors
D. all of these
A. all phase conductors
B. where used, the neutral
C. all equipment grounding conductors
D. all of these
a fitting is? part of a wiring system that is intended primarily to perform an electrical function, or a mechanical function? Source: Journeyman electrician exam questions and answers, Tom Henry, 2011; PP 27
mechanical function
appliance that is not easily moved from one place to another in normal use is a _______ appliance. Source: Journeyman electrician exam questions and answers, Tom Henry, 2011; PP 27
A. Fastened in place
B. Dwelling unit see.
C. Fixed
D. Stationary
A. Fastened in place
B. Dwelling unit see.
C. Fixed
D. Stationary
of the following the best indication of the condition of the charge of the lead acid battery is the __________? Source: Journeyman electrician exam questions and answers, Tom Henry, 2011; PP 28
D. specific gravity
in general, the most important point to watch the operation of transformers is the_______? Source: Journeyman electrician exam questions and answers, Tom Henry, 2011; PP 28
A. core loss
B. excitation
C. temperature
D. primary voltage
A. core loss
B. excitation
C. temperature
D. primary voltage
Wound Rotors are especially useful for what reason? Motors Second Edition 2010, PP 118 (NC set: wound rotor motor)
They are able to deliver high starting torque without overloading the electrical supply system.
What is the difference between a squirrel cage motor and a wound rotor motor? Motors Second Edition 2010, PP 118 (NC set: wound rotor motor)
The conductor bars are replaced with coils of wire.
The windings in a wound-rotor motor are wye or delta? Motors Second Edition 2010 PP 118 (NC set: wound rotor motor)
Either, and dual or single voltage.
The Rotor of a wound-rotor motor is different from a squirrel cage motor how? Motors Second Edition 2010 PP 119 (NC set: wound rotor motor)
The conducting bars are coils of wire, there are 3 slip rings, and an external resistance bank.
Wound-rotor motors may be delta or wye wound, to match what? Motors Second Edition 2010 PP 119 (NC set: wound rotor motor)
The stator: the rotor is wound to match their stator in this type of motor.
The rotor windings in a wound-rotor motor are marked what? Motors Second Edition 2010 PP 119 (NC set: wound rotor motor)
M1, M2, and M3.
External resistors are used to limit what? Motors Second Edition 2010 PP 118 (NC set: wound rotor motor)
Starting current and to create a more resistive circuit with more starting torque.
Brush material is usually composed of what, for high and low voltage machines? Motors Second Edition 2010 PP 120 (NC set: wound rotor motor)
High voltage: carbon and graphite
Low voltage: metallic powder and graphite
Note: graphite functions as a lubricant
The resistors used with the rotor in a wound-rotor motor are often referred to as what? Motors Second Edition 2010 PP 120 (NC set: wound rotor motor)
Secondary resistors, because the rotor is the secondary of the motor.
How much rotor current is carried by the resistors in a wound-rotor motor? Motors Second Edition 2010 PP 121 (NC set: wound rotor motor)
All of the current is carried by this in a wound rotor motor.
As the wound-rotor motor speed is reduced the frequency is raised, this affects an ammeter how? Motors Second Edition 2010 PP 121 (NC set: wound rotor motor)
The ammeter operates at 60 HZ and will not operate at higher HZ and lower motor speeds effectively.
A starter starts a wound-rotor motor with how much resistance in the circuit? Motors Second Edition 2010 PP 122 (NC set: wound rotor motor)
When the motor reaches full speed, what happens to the resistance? Motors Second Edition 2010 PP 122 (NC set: wound rotor motor)
Full resistance
It is switched out and the rotor windings are shorted in a wound-rotor motor. (Thus operating like a shorting ring in a squirrel cage induction motor.)
The resistors in a wound-rotor motor starter are designed for continuous operation? Motors Second Edition 2010 PP 122 (NC set: wound rotor motor)
What must be used in order to allow continuous operation of resistors after starting in a wound-rotor motor? Motors Second Edition 2010 PP 122 (NC set: wound rotor motor)
These in a wound-rotor motor are not designed for continuous operation.
A regulator, must be used in order to allow this i a wound rotor motor.
In a wound rotor motor, the starting torque decreases as the frequency decreases and the speed of the rotor increases, thereby reducing current and induction in the rotor and allowing resistance to be removed manually or automatically how? Motors Second Edition 2010 PP 122 (NC set: wound rotor motor)
manually with a rheostat (a series resistor limiting voltage) or automatically with a controller and.
For each step in acceleration in a wound-rotor motor, what happens to current and frequency in tcontactorshe rotor? Motors Second Edition 2010 PP 123 (NC set: wound rotor motor)
Why?
Current and Frequency in the rotor decrease as the rotor starts turning during startup. (summary motors PP 128)
When the speed of the wound-rotor motor rotor is reduced, what increases resulting in more current induced into the windings of the rotor? Motors Second Edition 2010 PP 125 (NC set: wound rotor motor)
Slip occurs as the speed of a wound-rotor motor rotor is reduced, resulting in more of this.
when a wound-rotor motor operates at a lower speed, what happens to normal ventilation and therefore speed? Motors Second Edition 2010 PP 125 (NC set: wound rotor motor)
The normal ventilation is reduced and therefore the speed is usually reduced no more than 50 percent.
The most common type of 3 phase motor is what? Motors Second Edition 2010 PP 385 & Electrical Field reference hand book NEC 2008 (NC set: wound rotor motor)
Squirrel cage induction type
In a wound-rotor motor, because some of the resistors in the rotor circuit are shunted, the resistance in the rotor circuit is what? What happens to rotor current? Motors Second Edition 2010 PP 124 (NC set: wound rotor motor)
Resistance in the rotor decreases and thereby the rotor current increases. Shunted means parallel.
Wound-rotor motor regulators are high or low wattage resistors? Meaning what? Motors Second Edition 2010 PP 125 (NC set: wound rotor motor)
High wattage, meaning they may remain in the circuit continuously to maintain speed. Versus a starter which cannot due to low wattage resistors.
Three common types of wound-rotor motor regulators are? Motors Second Edition 2010 PP 125 (NC set: wound rotor motor)
Drum switches, three pole rheostats, and silicone controlled rectifiers.
Of the three common wound-rotor motor regulator types, which one is used the least? Motors Second Edition 2010 PP 125 (NC set: wound rotor motor)
Silicon-controlled Rectifiers (SCR's). Because they are only used in applications that require continuous speed variations.
The equipment intended to connect and disconnect power circuits are known collectively as what? Keith H. Suker, Power Electronics design: a practitioner's guide, PP 15 (NC set: Switchgear)
Switchgear.
Switchgear are generally divided into how many groups and what are they? Keith H. Suker, Power Electronics design: a practitioner's guide, PP 16 (NC set: Switchgear)
Four:
Disconnect or isolator switches,
load brake switches,
circuit breakers, and
contactors.
Load brake switches are, or are not, designed to interrupt fault currents? Keith H. Suker, Power Electronics design: a practitioner's guide, PP 17 (NC set: Switchgear)
Load brake switches are not designed to interrupt fault currents; they must remain closed through faults.
Indoor breakers are usually what in regards to location and number, whereas outdoor breakers maybe what? Keith H. Suker, Power Electronics design: a practitioner's guide, PP 17 (NC set: Switchgear)
Indoor breakers are usually in metal cabinets as part of the switchgear lineup, Where as outdoor breakers maybe standalone units.
What must be remembered when using vacuum circuit breakers? Keith H. Suker, Power Electronics design: a practitioner's guide, PP 17 (NC set: Switchgear)
Chop current's as high as 3 to 5 A if the breaker is ahead of a transformer can generate a high-voltage exciting inductance of the transformer, and this can be passed on to secondary circuits.
Regarding chop current the required voltage control can be obtained with what on the primary and what on the secondary of the transformer? Keith H. Suker, Power Electronics design: a practitioner's guide, PP 17 (NC set: Switchgear)
Arrestors on the primary and MOV's on the secondary.
Nearly all relays are operated from what? Keith H. Suker, Power Electronics design: a practitioner's guide, PP 18 (NC set: Switchgear)
Current transformers and most are now solid state.
The real workhorses of switchgear are what? hint; they're rated for many thousands of operations. Keith H. Suker, Power Electronics design: a practitioner's guide, PP 18 (NC set: Switchgear)
Contactors: These are Electromagnetically operated switches that can be used for motor starting and general-purpose control.
Contactors can employ what at low voltages and medium voltages? Keith H. Suker, Power Electronics design: a practitioner's guide, PP 18 (NC set: Switchgear)
Airbrakes at low voltages or vacuum contacts at medium voltages.
Most contactors have what type of operating coils? Keith H. Suker, Power Electronics design: a practitioner's guide, PP 18 (NC set: Switchgear)
Continuously energized operating coils and open when control power is removed.
Motor starters can handle overloads of how many times rated or more? Keith H. Suker, Power Electronics design: a practitioner's guide, PP 18 (NC set: Switchgear)
Five times rated overload.
Lighting contactors also have overload ratings for? Keith H. Suker, Power Electronics design: a practitioner's guide, PP 18 (NC set: Switchgear)
Incandescent lamps.
MOVs will limit the developed voltage on opening but will be of no help in limiting what? Keith H. Suker, Power Electronics design: a practitioner's guide, PP 19 (NC set: Switchgear)
DI/DT that may interfere with other circuits.
Control and emergency transfer switch handles or pushbuttons shall be in a readily accessible location at an elevation of not over what? What would be an exception? NEC 490.41a (NC set: Switchgear)
6'7" An exception would be any switches requiring more than 50 pounds of force be at 66 inches or less in height.
Direct-current combined with alternating current is a common occurrence with electronic circuits this concept is used in many systems as what? NJATC, AC Theory 2nd edition 2009, PP 230 (NC set: AC filters)
As a base voltage and a signal voltage. The AC signals are sometimes referred to as an AC riding on a DC level.
AC riding on the DC level is very common in what type of circuits as the DC level is used to operate the amplifier components such as transistors and AC voltage is the signal we want to amplify? NJATC, AC Theory 2nd edition 2009, PP 230 (NC set: AC filters)
amplifier circuits.
The low pass filter blocks and passes what frequency range? NJATC, AC Theory 2nd edition 2009, PP 231 (NC set: AC filters)
The low pass filter blocks the high-frequency 100 kHz and passes the low-frequency 1 kHz.
What filter classification blocks DC? NJATC, AC Theory 2nd edition 2009, PP 231 (NC set: AC filters)
Transformer coupling, & capacitive coupling.
Transformer coupling of amplifier stages is often used in what? NJATC, AC Theory 2nd edition 2009, PP 231 (NC set: AC filters)
Audio amplifiers. These block DC voltage because they are essentially ignored.
Capacitive coupling is also known as what? NJATC, AC Theory 2nd edition 2009, PP 232 (NC set: AC filters)
RC filtering.
Capacitive coupling or RC filtering is also used when what must be done with the DC and AC voltage? NJATC, AC Theory 2nd edition 2009, PP 232 (NC set: AC filters)
Is used when the DC must be filtered out or blocked, and the AC part of the amplified voltage is allowed to pass.
The filter or coupling capacitor is an expensive or inexpensive method to block the DC level? NJATC, AC Theory 2nd edition 2009, PP 232 (NC set: AC filters)
Inexpensive.
The coupling capacitor works why? NJATC, AC Theory 2nd edition 2009, PP 232 (NC set: AC filters)
Because a capacitor does not allow dc voltage to pass, since it requires a change in voltage in order to discharge.
A simple low pass filter uses what in series with a load resistor? NJATC, AC Theory 2nd edition 2009, PP 232 (NC set: AC filters)
An inductor. As frequency increases so does XL, dropping more voltage across the inductor rather than the load.
In low pass filter and a high pass filter are designed to pass what at what frequency? NJATC, AC Theory 2nd edition 2009, PP 231 (NC set: AC filters)
Hi pass filters pass high frequencies and low pass filters pass low frequencies.
The half power point is what? NJATC, AC Theory 2nd edition 2009, PP 234 (NC set: AC filters)
The point at which the load resistance is dissipating half the max power that could occur at the load.
The half power point is typically the point where ______ percent of the source voltage appears at the load. NJATC, AC Theory 2nd edition 2009, PP 234 (NC set: AC filters)
70.7%. 70.7% of the current appears at the load as well. 70.7% voltage x 70.7% current equals 50% of the VA or power, or half PowerPoint.
All frequencies to lose less than one half maximum power at the coil are considered to pass to the load. All frequencies the produce more than one half power dissipation at the coil are considered what? NJATC, AC Theory 2nd edition 2009, PP 236 (NC set: AC filters)
Rejected and never reach the load.
A capacitive low pass filter does what at low frequencies? NJATC, AC Theory 2nd edition 2009, PP 236 (NC set: AC filters)
At low frequencies, the capacitor will exhibit a higher reactance, and most of the circuit current will flow through the load resistor rather than the capacitor branch.
A synchronous motor is a motor that rotates at the same speed as what? ATP & JATC, Motors 2nd edition, 2010: Chapter 7 Synchronous motors, PP 132
This motor rotates at exactly the same speed as the rotating magnetic field of the stator.
What type of motor is used with loads that require constant speed? ATP & JATC, Motors 2nd edition, 2010: Chapter 7 Synchronous motors, PP 132
Synchronous motors are used with these types of loads.
This type of motor is used for applications where a NEMA class B motor is desired. ATP & JATC, Motors 2nd edition, 2010: Chapter 7 Synchronous motors, PP 132
Synchronous motors are used with this NEMA class.
The rotor field winding in a synchronous motor is excited by what? ATP & JATC, Motors 2nd edition, 2010: Chapter 7 Synchronous motors, PP 132
This is excited by the external DC power source in a synchronous motor.
If the synchronous motor is overloaded to the point where the rotor is pulled out of step with the rotating magnetic field...
ATP & JATC, Motors 2nd edition, 2010: Chapter 7 Synchronous motors, PP 133
The armortisseur winding will now see relative motion and torque will be produced by the Armortisseur winding until the OSR, which is the current relay, trips the stator off-line or the motor resynchronizes.
The stator of a synchronous motor is constructed how? ATP & JATC, Motors 2nd edition, 2010: Chapter 7 Synchronous motors, PP 133
The stator of this motor is constructed like the stator of any polyphase motor, with the field coils placed in slots 120 electrical degrees apart.
Why is the stator constructed of laminated our sheets in a synchronized motor? ATP & JATC, Motors 2nd edition, 2010: Chapter 7 Synchronous motors, PP 132
This type of motor stator must be constructed in this way to minimize eddy current losses.
A synchronous motor has a how many part rotor? What are these parts? ATP & JATC, Motors 2nd edition, 2010: Chapter 7 Synchronous motors, PP 134
A two-part rotor with an induction-rotor section and a wound-rotor section in this type of motor.
Starting a synchronous motor as an induction motor requires this? ATP & JATC, Motors 2nd edition, 2010: Chapter 7 Synchronous motors, PP 134
This type of motor requires Armortisseur windings to start.
What is also referred to as damper windings In a synchronous motor? ATP & JATC, Motors 2nd edition, 2010: Chapter 7 Synchronous motors, PP 134
Armortisseur windings is another name for this.
In a synchronous motor the number of rotor fields must equal what? ATP & JATC, Motors 2nd edition, 2010: Chapter 7 Synchronous motors, PP 134
In this motor the number of rotor fields must equal the number stator field poles.
In a synchronous motor, the wound rotor section consists of field windings wrapped around what? ATP & JATC, Motors 2nd edition, 2010: Chapter 7 Synchronous motors, PP 134
In this motor the wound rotor section consists of field windings wrapped around salient poles.
What is it called when the DC excitation is applied to the rotor, creating an electromagnetic field with North and South poles locked with the revolving field of the stater? ATP & JATC, Motors 2nd edition, 2010: Chapter 7 Synchronous motors, PP 135
This is called locked in step, in a synchronous motor.
What statement describes a motor where no eddy currents are induced in the iron? ATP & JATC, Motors 2nd edition, 2010: Chapter 7 Synchronous motors, PP 135
A synchronous motor.
Why is the syncronous rotor also assembled from iron laminations? ATP & JATC, Motors 2nd edition, 2010: Chapter 7 Synchronous motors, PP 135
The heat induced into the core as a result of the eddy currents is detrimental to the service life of the motor.
Synchronous motors that typically run faster than this RPM are considered high-speed synchronous motors? ATP & JATC, Motors 2nd edition, 2010: Chapter 7 Synchronous motors, PP 135
more than 450 RPM.
The _______ of a synchronous motor has a DC field winding that creates electromagnetic fields. ATP & JATC, Motors 2nd edition, 2010: Chapter 7 Synchronous motors, PP 135
The rotor of a synchronous motor does this.
What type of synchronous motor designs do not include the armortisseur windings? ATP & JATC, Motors 2nd edition, 2010: Chapter 7 Synchronous motors, PP 136
Synchronous condensers do not include these.
In a synchronous motor, motors running at lower speeds with decreased centrifugal force compared to a high-speed rotor design, the spider ring is what? ATP & JATC, Motors 2nd edition, 2010: Chapter 7 Synchronous motors, PP 136
The spider ring in a synchronous motor that is low-speed is a hollow cylinder.
Some synchronous motor designs for synchronous condensers do not include what? ATP & JATC, Motors 2nd edition, 2010: Chapter 7 Synchronous motors, PP 136
These motors sometimes do not include the armortisseur.
What is also called a small DC motor? ATP & JATC, Motors 2nd edition, 2010: Chapter 7 Synchronous motors, PP 136
A pony motor is sometimes called this.
When a synchronous motor is started up it operates as what? ATP & JATC, Motors 2nd edition, 2010: Chapter 7 Synchronous motors, PP 137
Upon start up this motor operates as an induction motor.
At approximately what speed does the synchronous motor create DC excitation applied to the wound rotor section? ATP & JATC, Motors 2nd edition, 2010: Chapter 7 Synchronous motors, PP 137
At pproximately 95% of synchronous speed, a synchronous motor creates this.
In regards to a DC excitor generator, the polarity of the slip rings is, or is not, Critical? ATP & JATC, Motors 2nd edition, 2010: Chapter 7 Synchronous motors, PP 137
The polarity of the slip rings is not critical in this.
In A DC exciter generator the negative polarity slip ring typically weats faster than the positive ring due to what? ATP & JATC, Motors 2nd edition, 2010: Chapter 7 Synchronous motors, PP 137
Electrolysis causes this: because of this the ring should be reversed periodically to equalize the wear.
The DC power to the synchronous motor is often supplied by what? Located where? ATP & JATC, Motors 2nd edition, 2010: Chapter 7 Synchronous motors, PP 138
This is supplied by the exciter generator mounted on the end of the synchronous motor shaft.
A DC shaft mounted excitor generator typically is what? ATP & JATC, Motors 2nd edition, 2010: Chapter 7 Synchronous motors, PP 138
Shunt or compound wound DC generator with the Armature in parallel with the shunt field and it shunt field rheostat.
A DC shaft mounted exciter generator voltage is usually not higher than what voltage and the KW capacity of the excitor generator usually ranges from approximately what? PP 138
This is seldom more than 250V and the KW capacity is from 1 to 3% of the synchronous motor rating.
What is the motor generator set (MG)? ATP & JATC, Motors 2nd edition, 2010: Chapter 7 Synchronous motors, PP 138
A motor and a generator with shafts connected and used to convert one form of power to another form.
Areas with sealed systems that supply equipment such as a gas-fired boiler are? JATC Hazardous Locations, WB 7
unclassified locations
Heavier than air gases are those with a vapor density greater than? JATC Hazardous Locations, WB 7 & Hazardous Locations: 2nd ed. 2007 Int. Ass. of electrical inspectors, PP 23
1
Pyrophoric materials are what? and are used in what classified locations? JATC Hazardous Locations WB 7
Pyrophoric materials are materials that ignite in contact with the air, such as white phosphorus, and are therefore unclassified do to their extreme and uncontrollable volatility.
Which of the following are Class II location material groups? Group E, F, or G? Hazardous Locations WB 8
All
The division system of hazardous area classification divides Class 1 locations into how many material groups? JATC Hazardous Locations WB 8
4: group A,B,C, & D
The Zone system of hazardous area classification divides class I materials into how many groups? JATC Hazardous Locations, WB 8
3: IIC, IIB, IIA
MESG is an acronym used in hazardous classified areas meaning what? Hazardous Locations: 2nd ed. 2007 Int. Ass. of electrical inspectors,WB 8
Minimum equipment safe gap
What wiring method(s) are allowed in a class I zone 0 classified location? NJATC Hazardous Locations WB 8
What is the color coding for intrinsically safe circuits? NEC 504.80C
Only intrinsically safe, however intrinsically safe is allowed in any hazardous location in general purpose enclosures. 2011 NEC 504.10B
Light Blue
What material groups are provided for class 3 locations? Hazardous Locations: 2nd ed. 2007 Int. Ass. of electrical inspectors, WB 9
None
The flash point of a liquid involves what form? Hazardous Locations: 2nd ed. 2007 Int. Ass. of electrical inspectors,WB 10
vapor
Sealed systems, such as metal gas piping systems are generally considered to be ________ locations. Hazardous Locations: 2nd ed. 2007 Int. Ass. of electrical inspectors, WB 10
unclassified
Combustible dust is finely divided solid material __________ microns or less in diameter. Hazardous Locations: 2nd ed. 2007 Int. Ass. of electrical inspectors, PP16
420
Is risk analysis and determining if a location is hazardous a job done in the field? Hazardous Locations: 2nd ed. 2007 Int. Ass. of electrical inspectors, PP 18
NO. In many installations it will require involvement from one or more of the following engineering or design professionals: chemical, process, mechanical, fire protection, civil, environmental, structural, architectural and electrical.
Adequate ventilation is a condition where _________? Hazardous Locations: 2nd ed. 2007 Int. Ass. of electrical inspectors, PP 21
the concentration of combustible material does not exceed 25 percent of the lower flammable limit of the material being considered.
Some Halogenated liquid hydrocarbons with a flammable range but no flash point are considered what? Hazardous Locations: 2nd ed. 2007 Int. Ass. of electrical inspectors, PP 22
unclassified
Two key considerations for design of a ventilated area to create an unclassified location are what? Hazardous Locations: 2nd ed. 2007 Int. Ass. of electrical inspectors, PP 22
Hours of operation and the method of interlocks.
A commercial repair facility is unclassified when there are more than _________ air changes per hour. Hazardous Locations: 2nd ed. 2007 Int. Ass. of electrical inspectors, PP 22
4
Housekeeping in every situation should be provided as a supplement to dust source elimination and ventilation. True or False? Hazardous Locations: 2nd ed. 2007 Int. Ass. of electrical inspectors, PP 22
False
Explosion proof and dust-ignition proof enclosures are able or not able to contain explosions that occur inside? Hazardous Locations: 2nd ed. 2007 Int. Ass. of electrical inspectors, PP 23
Are able, however they both prevent gases or dust from entering the enclosure and prevent explosions inside the enclosure first. JATC Hazardous Locations WB 21
The primary wiring method for hazardous locations under the Division System continues to be _____, While the primary wiring method used in the Zone system is ____. Hazardous Locations: 2nd ed. 2007 Int. Ass. of electrical inspectors, WB PP 19
Division- conduit
Zone- cable type
Equipment marking shall specify the class, but division if the equipment is suitable for _________only. NEC 500.8(c)1 &2
Division 2
As Heavier than air gases are heated, they behave how? Hazardous Locations: 2nd ed. 2007 Int. Ass. of electrical inspectors, PP 23
They become lighter.
What is required at the vertical and horizontal boundaries of the classified locations? Hazardous Locations: 2nd ed. 2007 Int. Ass. of electrical inspectors, PP 19 figure 1-03 Note 3
Sealing fittings
Both the Division and Zone systems can be used in the same facility as long as what? Hazardous Locations: 2nd ed. 2007 Int. Ass. of electrical inspectors, PP 25
Only as long as they don't overlap.
In what areas, the abnormal condition, or first fault, would have to occur in the containment system for the flammable or combustible material before an ignitible concentration could occur? Hazardous Locations: 2nd ed. 2007 Int. Ass. of electrical inspectors, PP 37
Division 2, Zone 2, or Zone 22
In addition to being wrench tight, the number of threads required to be engaged into explosion proof equipment entries is ______, whereas threaded joints must be_____. 2011 NEC 505.9E1 exc. 1
threaded joints- 5
threaded entries- 4 1/2
What is the maximum spacing for labeling of intrinsically safe wiring raceways, cable trays, and other wiring methods? NEC 504.80B
25 feet
A combustible gas detection system is a protection technique that is limited to what? JATC Hazardous locations WB PP 23
Limited to industrial establishments
Define the word approved as described in article 100 of the 2011 NEC.
Acceptable to the authority having jurisdiction.
Usually the AHJ will base approvals on the use of? Hazardous Locations: 2nd ed. 2007 Int. Ass. of electrical inspectors, PP 73
Listed and labeled equipment.
A nonincendive circuit does not include what type of wiring? NEC 500.1
Field wiring
The symbol AEx in Zone equipment marking refers to what? Hazardous Locations: 2nd ed. 2007 Int. Ass. of electrical inspectors, PP 79
Built to American Standards
If equipment under the zone system is identified with E, what protection technique is incorporated in the equipment? JATC Hazardous Locations, Hazardous Locations: 2nd ed. 2007 Int. Ass. of electrical inspectors, WB PP 33
Increased safety NEC 505.9C2(4)
Conduit seals are required to be listed and installed in what locations? Hazardous Locations: 2nd ed. 2007 Int. Ass. of electrical inspectors, WB PP 41 & 2011 NEC 501&2.15C1 fittings
What class hazardous location does not address seals
Accessible
Class 3
Conduit seals shall be installed within _____ of the enclosure. NEC 501.15A1
18 inches
Metal conduit that contains no unions, couplings, boxes, or fittings, and passes completely through a class 1, Div 1 location with no fittings less than _____ beyond each boundary, shall not require a conduit seal if the termination points of the unbroken conduit are in _______. NEC 501.15A4
12 inches
unclassified locations
Examples of fittings employing other than NPT threads include? 2011 NEC 505.16B1 informational note
conduit couplings
capped elbows
unions
breather drains.
Type of protection where electrical parts capable of igniting an explosive atmosphere are fixed in position and completely surrounded by filling material such as ______ to prevent the ignition of an external explosive atmosphere is what? 2011 NEC 505.2 definitions
glass or quartz powder
powder filling Q
Combustible metallic dusts are covered by article 506 of the 2011 NEC Zone 20, 21, and 22 locations for combustible dusts or ignitible fivers/ flyings?
Are not NEC 506.1
In conduit seals the conductor fill is not permitted to exceed _____ percent of the cross sectional area of the conduit unless specifically listed for a higher percentage. 2011 NEC 501.15C6
25
Author
johnbowens
ID
349659
Card Set
Subject Matter Expert Electrical
Description
this is a subject matter expert study guide for high level questions regarding data centers that may be expected in an interview.