An individual branch circuit to one load can be what size? PP 5
Branch circuits to more than one load are rated at what amperage?
Any.
15, 20, 30, 40, and 50 only.
Lampholders using branch circuits in excess of 20 amp shall be not less than how many watts and of what type? PP 5
660 W heavy-duty type. 210.21a
A 20 amp rated duplex receptacle is to be loaded to 20 amps. And a single 20 amp receptacle is to be loaded to what? PP 6 Tom Henry’s 2011
A single 20 amp receptacle can only be loaded to 16 A. According to the table to 210.21 B2, which is titles "Receptacle" indicating one and not multiple.
According to section 210.23(A1) the rating of any one cord-and plug-connected utilization equipment, not fastened in place, shall not exceed ______% of the branch circuit rating. Whereas, utilization equipment fastened in place, other than luminares, shall not exceed _______% of the branch circuit rating.
A. 80/125
B.125/80
C.100/125
D.80/50
A. 80/125
B.125/80
C.100/125
D.80/50
According to section 210.23(A2) the total rating of utilization equipment fastened in place shall not exceed _____ % of the branch circuit rating.
50%
What can be used where the ampacity of the conductor does not meet the standard size of the ocpd? PP 10
The next higher size OCPD. 240.4B2
What is the reason for limiting a load to 80%? PP 11
The reason for limiting the load to 80% is not that the conductors can't carry the continous load. The 80% is a current limitation on the over current device to limit the heat that may affect the breaker in the panel.
Are nuetral conductor load calculated at continous?
NO. PP 11 Since the Nuetral conductor has no heating effect on the OCPD
Are line side service conductors calculated as continuos? Why? PP 11
No. Because they are not connected to an OCPD and therefore have no heating effect to the OCPD and do not need to be rated at 80%
Branch circuits for electric heat and 120 gallon or less water heaters are calculated at what?
as continous per 424.3B and 422.13
Table 220.44 is for branch circuits? yes or no? Why?
No. It is for feeders because it is in Article 220: branch circuit, FEEDER, and service calculations and the table gives values at 10kva and over, which would exceed a branch circuit value.
Receptacle are considered a continuos load? T or F?
No. Receptacles are generally not considered a continous load. PP 14 Tom Henry’s 2011
The term Equipment: is a general term including fittings, and devices? used in connection with an electrical installation?
Yes. PP 18
according to section 210.23A1 the rating of any one cord and plug connected utilization equipment shall not exceed what % of the branch circuit rating? consider this as a continuos or non-continuous load to answer the question.
80% for any one cord and plug connnected equipment. This would be the same as continuous rating even though a receptacle is not a continous load.
What loads add heat to the neutral? Please give some examples.
Non-linear loads. pp 22
Some examples of nonlinear loads that can generate harmonic currents are computers, fax machines, printers, PLCs, refrigerators, TVs and electronic lighting ballasts. Personal computers constitute nonlinear loads since they incorporate switched-mode power supplies. The PC current is mainly dominated by the third and fifth harmonic components.
A nonlinear load in a power system is characterized by the introduction of a switching action and consequently current interruptions. This behavior provides current with different components that are multiples of the fundamental frequency of the system. These components are called harmonics. The amplitude and phase angle of a harmonic is dependent on the circuit and on the load it drives. For a fundamental power frequency of 60 Hz, the 2nd harmonic is 120 Hz, the 3rdharmonic is 180 Hz, and so on. The harmonic currents flow toward the power source through the path of least impedance.
Does an optional method exist for calculating feeder loads for a commercial building?
No. PP 270 Code calculations 2008
Are the feeder demand for receptacle loads in a commercial building calculated with the lighting load as they are for a residence?
No, they are not. PP 271 Code Calculations 2008
The code recognizes two methods of calculation. One is the standard method, usually called the _______method, and the other is the optional method, usually referred to as the _________ method.
long, and short. PP 246 Code Calculations 2008
general purpose receptacles in a dwelling unit are included, or not, in the volt a meres per square foot (VA per sq ft) calculation?
They are. PP 247 Code Calculations 2008 and Table 220.12 note
Which is greater, the BCSC (branch circuit selection current) or the RLC (Rated load current)? What type of motor is BCSC usually found on?
The branch circuit selection current is always equal to or greater than the rated load current. This applies to Hermetic refrigerant motor compressors generally. The nameplate usually gives circuit breaker rating. PP 187 Code Calculations 2008
Pertaining to motors, the horsepower rating of the disconnect switch can be the same as the horsepower rating of the motor as long as?
As long as there is no code letter, or the code letter is between A and F, the horsepower rating of the disconnect switch can be the same as the horsepower rating of the motor.
the formula for applying correction factor regarding ambient temperature to Table 310.15B16 to achieve the required minimum ampacity is what?
LOADCORRECTION FACTOR
Or 20 amps = 16 amps
125%
Tom Henry’s Calculations PP 39, 2011
The ** in table 310.15B16 apply to motor circuits? True or False?
Why?
The ** rules for over current protection do not apply to motor circuits per 240.4G, 2011 NEC & Tom Henry’s Code Calculations PP 41, 2011
Motors have overload or thermal protection versus lighting circuits, etc.
required working clearance is 30 inches for 600 volts and less, or the ___________ whichever is greater. NEC 110.26A2 2011
Width of the gear
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
The general rule is 100 amps or less is wire sizes ____________ with ______C ampacity and for over 100 amps the wire size is _________ and larger with _____C.
14-1 is 60C
1/0 and larger is 75C
A neutral conductor which carries only the unbalanced current from the other conductors, of the same circuit (shall) shall not, be required to be derated per 310.15B3a?
A 3 wire (2 hots and a neutral) in a Wye connected system (shall) shall not be derated?
A neutral conductor which carries only the unbalanced current from the other conductors shall not be derated per 310.15b3a. NEC 310.15b5a, 2011 and Tom Henry’s code calcs PP 55, 2011.
A 3 wire system such as a wye system with 2 hots and a neutral shall be derated
Identified as used in the code in reference to a conductor or it’s terminals means that such a conductor or terminal is to be recognized as?
A grounded conductor 200.1
When soldering conductors flux is used to? Tom Henry’s JW Book PP 5
To keep the surface clean
A motor with a wide speed range is a? AC, synchronous, induction, or DC? Tom Henry’s PP 4
DC.
To lubricate a motor sleeve bearing you would use what? Tom Henry’s PP 5
oil.
An instrument used to measure electrical energy is called the wattmeter or watt-hour meter? Tom Henry’s PP 5
Watthour meter.
What is the difference between resistance and reluctance?
Resistance is the Property of a circuit to tend to prevent the flow of current and at the same time causing energy to be converted into heat. Whereas In a DC field, the reluctance is the ratio of the "magnetomotive force” (MMF) in a magnetic circuit to the magnetic flux in this circuit. In a pulsating DC or AC field, the reluctance is the ratio of the amplitude of the "magnetomotive force” (MMF) in a magnetic circuit to the amplitude of the magnetic flux in the circuit.
In a residence the wall switch controlling the ceiling light is usually? Tom Henry’s PP 7
a.Connected across both lines
b.The double pole switch
c.Connected in one line only
d.A four way switch
a.Connected across both lines
b.The double pole switch
c.Connected in one line only
d.A four way switch
The branch circuit loads specified by the code for lighting and receptacles are considered? 220.14 Tom Henry’s PP 7
A. Minimum loads
B. maximum loads
C. Loads to be served
D. Peak loads
Minimum loads
What is the use for a wound rotor? Tom Henry’s Code Calcs, PP 70
wound rotors are AC motors with slip rings used in speed control applications.
The non-time delay fuse will hold ________ times its rated current for about _______, Dual element (time delay fuses) will hold ______their rating for _______. Tom Henry’s Code Calcs, PP 70
5 times for 1/4th of a second
5 times for 10 seconds
Will fuses open all ungrounded conductors at the same time? Tom Henry’s Code Calcs, PP 70
no. An example would be a transformer for temp power fed from a 60 amp disconnect opening one leg because the xfmr never derived a neutral. IE; not connected. Causing 240 with the load plugged in, but otherwise appearing normal with a voltage tester.
The commutator of the generator should be cleaned with which of the following?
A. Emery cloth
B. graphite
C. smooth file
D. fine sandpaper
Tom Henry
s JW exam book PP 8
A. Emery cloth
B. graphite
C. smooth file
D. fine sandpaper
Electron is a Greek word for? Tom Henrys JW exam book PP 10
amber
True or false? A large series motor should not be started without some load on it because it will Develop excessive speed and damage itself. Tom Henrys JW exam book PP 11
True.
A wattmeter mesures?
A. AC power only
B. DC reactive power only
C. AC and DC
D. none of these
A. AC power only
B. DC reactive power only
C. AC and DC
D. none of these
If the needle of the VOM (voltmeter) will no longer align with the zero mark at the lowest range of resistance but will align on the other resistance ranges the probable cause is the? Tom Henrys JW exam book PP 11
supply battery is weak.
A battery that cannot be recharged is a? Tom Henrys JW exam book PP 11
primary cell
Define inter tier connector: where is this found in the NEC?
an electrical conductor used to connect two cells on different tiers or shelves of the same rack.
article 480 storage batteries.
The most common nominal battery cell voltage are what for what type of battery?
2 volts per cell for the lead acid systems.
article 480 nec.
On a drawing: a circle with the B stands for? Tom Henrys JW exam book PP 12
outlet with blank cover
The meter used to test the armatures and stators of electric motors generators and other equipment for a short circuit is called a? PP 13
growler
Note: A short in the coil creates a closed circuit that will act like the secondary coil of a transformer, with the growler acting like the primary coil. This will induce an alternating current in the shorted armature that will in turn cause an alternating magnetic field to encircle the shorted armature coil. A flat, broad, flexible piece of metal containing iron is used to detect the magnetic field generated by a shorted armature. A hacksaw blade is commonly used as a feeler. The alternating magnetic field induced by a shorted armature is strong at the surface of the armature, and when the feeler is lightly touched to the iron core of an armature winding, small currents are induced in the feeler that generate a third alternating magnetic field surrounding the feeler.
What type of motor has no commutator? Tom Henrys JW exam book PP 13
A. Shunt
B. induction
C. universal
D. repulsion
AC Motor is an adequate answer.
Which of the following has the least number of valence electrons? Tom Henrys JW exam book PP 14
A. Insulator
B. semi insulator
C. conductor
D. semi conductor
A. Insulator
B. semi insulator
C. conductor
D. semi conductor
Four covalent bonds. Carbon has four valence electrons and here a valence of four. Each hydrogen atom has one valence electron and is univalent.
Feeder conductor size section 430.24; conductors supplying two or more motors shall have an ampacity equal to what? Tom Henry Calculations 2011
Equal to the sum of the full current rating of all of the motors, plus 125% of the highest rated motor in the group.
article 626?
Electrified truck
Article 517 is what?
healthcare facilities
What is the minimum size grounding electrode conductor required by Article 250 to building steel, when the service entrance conductors are parallel 250 KCMIL copper?
The table 250.66 denotes Size of Largest Ungrounded Service-Entrance Conductor equivalent Area for Parallel conductors (AWG/kcmil ) Therefore the 250 parallel need to be added together for the 350 through 600KCMIL size and a 1/0 copper would be sufficient.
When using an effectively grounded metal water pipe to ground a separately derived system transformer, as an Article 250 general rule?
A. It must be connected as near as practicable to the system electrode conductor connection’
must be connected as near as practicable to the system
B. both A & B above are true.
C. neither A or B above are required.
It must be connected as near as practicable to the system electrode conductor connection’
must be connected as near as practicable to the system
article 230 covers what?
Services
Minimum size and rating of service-entrance conductors before the application of any adjustment or correction factors shall not be less than the sum of the noncontinous load plus 125 percent of the continous load. What is an exception?
Grounded conductors that are not connected to an overcurrent device shall be permitted to be sized at 100 percent of the continous and noncontinous load. NEC 230.42 A1 Exc.
Regarding the conductor size of service-entrance conductors over 600 volts, nominal... they "shall not be smaller than ______awg, or ____awg in a multiconductor cable.
6 awg, or 8 awg in a multi-conductor cable. NEC 230.202A
A service point is the point of connection between the facilities of the serving utility and the premises wiring, regarding underground conductors, the point shall be considered what if there are no terminal box, meter, or other enlcosure?
The "point of connection" shall be considered the point of entrance of the service conductors into the building. NEC 100 Service Conductors, underground: EXC.
A service Lateral can be overhead? True or false?
False. By definition a service lateral are The underground conductors between the utility electric supply system and the service point.
Regarding GFPE, The rating of the service disconnect shall be considered to be the rating of the _______ that can be installed or the highest___________ for which the actual overcurrent device installed in a circuit breaker is rated or can be adjusted.
An exception is what?
largest fuse
continous current trip setting
NEC 230.95
An exception is a service disconnect for a continous industrial process where a nonorderly shutdown will introduce addtitional or increased hazards. NEC 230.95 EXC
A ground fault protection system serves only to limit damage to what and where during what type of event?
GFP serves only to limit damage to conductors and equipment on the load side in the event of an arcing ground fault on the load side of the protection element. NEC 230.95 C infor. note 1
Where the the grounding electrode conductor is connected to rod, pipe, or plate electrodes, that portion of the conductor that is the sole connection to the grounding electrode shall not be required to be larger than _______CU or ______AL AWG wire. NEC 250.66A
6 awg CU or 4 awg AL
All mechanical elements used to terminate a gronding electrode conductor or bonding jumper to a grounding electrode shall be what? NEC 250.68A
Accessible. Meaning the obstruction can be removed, versus readily accessible. Encased or burried is an exception.
What must be remembered about a metal elbow that is installed in an underground nonmetallic raceway?
That as long as the metal portion is burried atleast 18 in to any part of the elbow it shall not be required to be connected to the grounded system conductor or grounding electrode conductor. NEC 250.80 EXC
A single rod, pipe, or plate electrode shall be _______.
Supplemented by one of the following: rod, pipe, or plate.... see nec for additionals. NEC 250.53A2
What is the minimum distance apart from rod, pipe, or plate electrodes?
6 ft apart minimum. NEC250.53A3
Are spliced conductors allowed on service entrance cables?
Yes according to 110.14a as long as they’re listed… and of course enclosed.
A building or structure is permitted to be supplied by an additional service for all but which of the following installations?
A. Fire pumps
B. different rate schedules
C. HVAC equipment
D. All of the above
…. with capacity requirements in excess of 2000 A at a supply voltage of 600 V or less. NEC 230.2A-D
A. Fire pumps
B. different rate schedules
C. HVAC equipment
D. All of the above
Cover is defined as what? NEC table 300.5 note 1
Shortest distance to the top of the conduit.
The provisions of part eight of artical 230 services exceeding 600 V nominal applies to what side of the service point?
Load side only NEC 230.200. Any and all of NFPA 70, the NEC, is always on the load side of the service and the line side applies to the serving utility.
Article 680 of the NEC covers what?
Swimming pools, fountains, and similar installations
All 15 and 20 and single phase 125 V receptacles located within how many feet of the inside walls of the pool Shall be protected by GFCI?
20 ft. NEC 680.2 A4
A medium voltage cable is rated ________volts and higher.
2001. NEC 328.2
Size of pull and juction boxes, conduit bodies, and handhole enclosures, for straight pulls: The length of the box shall not be less than ______ times the outside diameter of the largest shielded conductor. (OR)
The length shall not be less than ______ times the outside diameter of the largest nonshielded conductor or cable.
48 times bare
32 times shielded
NEC 314.71A
Where can working spaces about energized gear be determined in the NEC?
T110.34a
The NEC test question “A garbage disposal is allowed to be cord and plug connected as long as the cord is no longer than_________.” Can be found where in the code?
A. Artcile 210 branch circuits and dwelling receptacle requirements
B. Article 400 Flexible cords and cables
C. Article 422 Appliances
D. All of the above
A. Artcile 210 branch circuits and dwelling receptacle requirements
B. Article 400 Flexible cords and cables
C. Article 422 Appliances
D. All of the above
422.16(b)3 receptacles shall not be less than 18” or more than 36” and a grounded type plug is not required if it is double insulated.
In what section of the NEC is a 32 volt transformer covered?
250.20A (grounding)
AC systems of less than 50 volts shall be grounded under any of what 3 conditions? 250.20A
1. if the supply transformer exceeds 150V to ground
2. if the supply transformer is ungrounded
3. where outside and overhead
Where would you find information in the NEC on “show windows”?
article 210.62 (branch circuits)
What does it say for amperage and linear footage and distance from the top of A show window?
one single phase 15 or 20A receptacle within 18 in of the top of the window and for each 12 linear ft. 210.62
Is a show window receptacle required for a 24v outlet?
yes. 210.62
What luminaries are permitted to be externally wired?
Chain-supported luminaries used in a show window. 410.14
Using NEC 700.10 as an example, what is the difference between marked and identified when using the following cited code as opposed to the definition of identified? “emergency circuits shall be permanently marked so they will be readily identified as a component of an emergency system”
marked by color to identify a given system; whereas, identified per article 100 definitions means identified is “recognized as suitable for the specific purpose, function, use, environment, application, and so forth. Note: Marked is not defined in the NEC.
Per 700.10B "To ensure that a fault on the normal wiring circuits won’t affect the performance of emergency wiring or equipment, keep all wiring to emergency loads independent of all other wiring. These exceptions apply to:”? -ECMweb.com
1. transfer equipment enclosures.
2. in emergency or exit luminaries
3. load control relay
4. j-box attached to emergency system and in unit equipment.
Courtesy ECMweb.com
What must be remembered about transfer switches and emergency systems versus other loads?
The alternate power source is permitted to supply other loads in addition to emergency loads; however, the transfer switch for emergency loads can only supply emergency loads.
courtesy ECMweb.com
504.80 states that instrinsically safe conduit bust be labeled what color and every how many feet?
blue and every 25 ft.
Where can you find grouping of disconnects? And how many disconnects can be grouped together?
230.72. If you said article 230 that would be close enough. And the maximum is 2 to 6 disconnects which are switches or SETS of circuit breakers.
According to 250.53(A)3 a supplemental ground rod must be separated from the other by how far? Be driven how deep into the soil? And this implies how many ohms or less are required for lightning protection? Last, what is the length required for a lighting ground rod per NFPA 780?
-6 feet separation at least 8 feet buried
-at 25 ohms or more, unless attached to a water pipe, then an additional ground rod is required anyhow.
-This means 50 ohms or less are required to ground for lightning protection.
-10 feet for a lightning protection ground rod.
250.53(a)3 under supplemental ground rods, informational note: What is increased by spacing the ground rods at twice the length of the rod (versus 6ft per code)?
parallel efficiency.
For a feeder or branch circuit disconnecting means (Art 225.39 outside branch circuits and feeders) the rating shall in no case be less than what for One circuit installations, 2 circuit installations, one family dwelling, and all others?
one circuit- 15A
2 circuit- 30A
one family- 100A
all other- 60A
Conduit fill percentage for table 4 chapter 9 is what, for 1 wire, 2 wires, or 3 wires or more? Why is the 2 wire out of ratio with the others?
53% one
31% two
40% three
The two wire would be a single phase load and does not carry the imbalance between two loads and therefore must be counted as a current carrying conductor per 310.15 meaning more heat in the conduit. Remember: the heat into the panel affecting the circuit OCPD is why we derate.
250.64(c) If you are putting number 6 grounding conductor on a cable tray and bonding to a bonding plate, this becomes what? And what does this mean?
It becomes part of the grounding electrode conductor and must be irreversibly crimped. Remember a grounding electrode per Art. 100 is “A conductor used to connect the system grounded conductor or the equipment to a grounding electrode or to a point on the grounding electrode system.”
Where would you find in the NEC the largest grounding electrode size to a rod, pipe, or plate?
250.66 largest is 6AWG copper or 4AWG aluminum.
Where would you find in the NEC isolated grounding receptacles?
Art. 406.3(d) C.A.P.S. “receptacles, cord connectors, and attachment plugs.”
What should copper never come into contact with due to electrolysis?
Aluminum. The metal would deteriorate over time trying to find a balance between valance electrons. According to 110.14
A neutral conductor, one that carries ONLY unbalanced current, versus a grounded conductor which does not, shall be derated? Y/N
No. 310.15(b). However Lighting neutrals would be counted.
Under article 500, what type of material does not apply to gas, dust, or ignitable filings?
pyrophoric: liable to ignite spontaneously on exposure to air. such as phosphorous
What size must conduit be for use as an equipment grounding conductor?
250.52 3/4 trade size or larger.
Single motor taps: no conductor to the motor shall have an ampacity less than (ratio) ________ that of the branch circuit conductors, and to the overload be no morethan 25 ft long. Conductor shall be enclosed. For GFPE to a manual motor controller: ampacity of the tap conductor shall be no less than (ratio)_____ GFPEprotection, not more than 10ft long, and have an ampacity not less than the branch circuit conductors.
1/3rd to overload device.
1/10th GFPE and branch OCPD to manual controller.
430.53(d)
What is the nipple conduit length under which derate will not be applied, and what is the conduit fill percentage? Where can you find this?
24 inches or less there is no derate 310.15(b)3
Chapter 9 Note 4: Maximum fill is 60%
Any “box” with any dimension over 6 feet will require what of the conductors in the box?
They must be cabled or racked per 314.28(b)
Burial depth for cables is found where? 0-1000v and 1000 volts and more?
300.5 is less than and 300.50 is more than.
Underground direct-buried cables that are not encased or protected t?y concrete and are buried (30 in.) more below grade shall have their location.
identified by a warning ribbon that is placed in the trench at least 300 mm (12 in.) above the cables.
Where is it stated that a conduit run must be complete before installation of conductors? NEC.
300.18 Raceway Installations (A) Complete Runs. Raceways, other than busway s or exposed raceways having hinged or removable covers, shall be installed complete between outlet, junction, or splicing points prior to the installation of conductors.
What size conductor is allowed to be installed in parallel?
310.1 O (H) Conductors in Parallel. General. Aluminum, copper-clad aluminum, or copper conductors, for each phase, polarity, neutral, or grounded circuit: shall be permitted to be connected in parallel (electrically Joined at both ends) only in sizes 1/0 AWG and larger where installed accordance with 310.10(H)(2) through (H)(6)
impedance of a circuit in an aluminum raceway or alluminum-sheathed cable differs from the impedance of the circuit in a steel raceway or steel-sheathed cable; therefore?
Separate raceways and cables must have the same physical characteristics.
When conductors are ran in parallel and an equipment ground is ran in each conduit, the equipment ground size is?
sized up because it is based on overcurrent device size from table 250-122.
400.10 pull at Joints and Terminals flexible cords and cables shall be connected to devices and to fittings so that tension is not transmitted to joints or terminals. informational Note: Some methods of preventing pull on a cord being transmitted to joints or terminals include?
knotting the cord, winding with tape, and using support or strain-relief fittings.
Where would you find feeder demand factors for elevators?
T620.14
At least 150 mm (6 in.) of free conductor, measured from the point in the box where it emerges from its raceway or cable sheath, shall be left at each outlet, junction, and switch point for splices or the connection of luminaires or devices. Where the opening to an outlet, junction, or switch point is less than 200 mm (8 in.) in any dimension, each conductor shall be long enough to extend at least 75 mm ______ outside the opening. This is found where?
(3 in.) 300.14 Length of Free Conductors at Outlets, junctions, and Switch points
400.4 Notes-Cords that comply with the requirements for outdoor cords and are so listed shall be permitted to be designated as weather and water resistant with the suffix ‘W” after the Code type designation. Cords with the “W” suffix are suitable for use in?
wet locations and are light resistant.
400.4 Notes: Cord types _______shall be permitted in lengths not exceeding 2.5m (08 ft) where attached directly, or by means of a special type of plug, to a portable appliance rated at _____ or less and of such nature that extreme flexibility of the cord is essential.
TFT and TST
50 watts
Regarding a service entrance conductors versus a feeder, passing through a 2nd building to supply a third, can a feeder or a service supply a 3rd building?
A service cannot involve a 3rd building whereas a feeder can, but requires a disconnect, unless it is outside the third building, under at least 2 inches of concrete for instance.
230.3 One Building or Other Structure to Be Supplied Through Another: Service conductors supplying a building or other structure hall not pass through the interior of another building or other structure.
225.31 Disconnecting Means: shall be provided for disconnecting all ungrounded conductors that supply or pass through the building or structure.
The term “supply conductors” is defined or not in the NEC. And if it is, where would it be defined? What is a supply conductor?
It is not defined under article 100 but is in the article 250.102 under bonding conductors and equipment…
Informational Note: The term supply conductors includes ungrounded conductors that do not have over current protection their supply side and terminate at service equipment or the first disconnecting means of a separately derived system.
