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What device is used to isolate sections of a switchboard after a casualty?
Disconnect links.
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How many disconnect links are used for each phase?
One per phase.
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What distributes the power within the switchboard?
Switchboard bus bars.
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The designation S A or S means what when referring to switchboards?
To identify different switchboard sections.
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Is it allowable to open or close disconnect links on an energized switchboard?
Never.
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What is the maximum number of circuits used in a power panel?
16.
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How will shore power connected with the incorrect phase sequence effect a three-phase motor?
The motor will operate in the opposite direction.
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What is installed on the switchboard to indicate that all three phases of shore power are energized?
Three neon lamps that light when the phases are energized.
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What is the function of a transformer bank?
To reduce the voltage from 450 volts to 115 volts for lighting distribution.
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Circuit breakers are provided to provide switching operations, circuit protection and?
Circuit isolation.
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What determines the maximum allowable voltage a circuit breaker can withstand?
The frame of the circuit breaker.
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What part of a circuit breaker senses an overload condition?
The trip element.
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Circuit breakers are classified in what manner?
Trip free or nontrip free.
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What are three circuit breaker time-delay ratings?
Instantaneous, short time delay, long tune delay.
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What are three types of circuit breaker trip elements?
Thermal, magnetic and thermal-magnetic.
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What determines the amount of current needed to trip a circuit breaker equipped with a magnetic trip element?
Depends on the size of the gap between the trip bar and the magnetic element.
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What type of circuit breaker trip element uses a bimetallic element?
A thermal trip element.
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What type of circuit breaker is used to connect ship's service generators to the power distribution system and bus ties?
ACB
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When a circuit breaker is used to connect ship's service generators to the switchboard what must be installed?
A reverse-power relay.
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What type of circuit breaker is used to protect single-load circuits and feeder circuits coming from a load center or distribution panel?
AQB.
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On a AQB-250 circuit breaker the designation 250 stands for what?
The frame size.
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What type of circuit breaker uses automatic trip devices that are trip-free?
AQB-A250
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What type of circuit breaker combines the AQB circuit breaker features with a current-limiting fuse unit?
AQB-LF250
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What does the designation LF mean on a AQB-LF250 circuit breaker?
Limiting fuse type.
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What function does the Current-limiting fuse unit provide on a AQB-LF250 circuit breaker?
Interrupts the circuit when the current is more than the interrupting rating of the breaker.
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AQB-LF250 circuit breaker has an interrupting rating of?
100,000 Amperes at 500 Volts, 60 Hz.
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The AQB-A250 circuit breaker has an interrupting rating of?
20,000 Amperes at 520 Volts, 60 Hz.
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What is the difference between a AQB-A250 circuit breaker and a NQB-A250 circuit breaker?
The NQB-A250 has no automatic tripping feature.
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ALB circuit breakers are designated in what manner?
Low-voltage, automatic circuit breaker.
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The continuous duty rating range of an ALB circuit breaker is?
5 to 50 Amperes at 120 Volts AC or DC.
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The major difference between a NLB circuit breaker and a ALB circuit breaker is?
They have no automatic tripping device.
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How does an ABT on a three-phase unit work?
It senses a decrease in voltage across any two of its three phases.
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How is a MBT shifted from normal to alternate source of power?
- 1. Ensure the alternate power source light is illuminated
- 2. Operate the normal power circuit breaker
- 3. Shift the interlock
- 4. Close the alternate power circuit breaker.
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Circuit breakers should be carefully inspected and cleaned at what interval?
Once a year.
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Before shifting MBT's from whom must you request permission?
The Engineering Officer of the Watch (EOOW).
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What is the most common type of circuit breaker used in an MBT?
A NQB circuit breaker.
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Does energy transferred by a transformer decrease in frequency?
No, usually there are changes in voltage and current only.
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What advantages do transformers provide?
Virtually maintenance free, simple, rugged and durable construction.
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What type of transformer operates with the primary connected across a Constant-potential source, providing a secondary voltage that is substantially constant from no load to full load?
A Constant-potential transformer.
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How many windings are found in a typical transformer?
Two.
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How often should a passive ground detector voltmeter or ground detector lamp system be checked?
Hourly during the watch.
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What is the minimum distance that the power cable metal armor or lead sheath should be cut away to allow for creepage between the armor or sheath and the terminal lug?
3 inches.
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Where does moisture usually collect in power cables?
Usually confined to the cable ends.
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After a moisture laden cable has been dried out using a heat process the cable should be immediately sealed with what?
A HF type plastic sealer.
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What is the maximum distance between the deck and cable hangars?
Six feet four inches.
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Shipboard electrical cable inspection deficiencies are categorized in what manner?
Category 1 - Immediate hazard, Category 2 - Potential hazard, Category 3 - Non hazardous.
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What is the maximum allowable amount of splices per electrical cable?
Two.
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The insulation of cables should be checked for resistance at what periodicity?
Quarterly.
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Where would a power cable designated as 40-4P-2-121-1 originate?
Load center 40.
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What do the following power cable voltage designators indicate, 1, 2 and 3?
1 = 100-199 volts, 2 = 200-299 volts, 3 = 300-399 volts.
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A power cable with the designation of "C" would be used in what application?
1C Communications.
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Power cables designated for casualty or emergency lighting use would be marked in what manner?
Casualty = C = Casualty power. Emergency = EL = Emergency lighting.
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What type of fuse is constructed so that it can be screwed into a socket mounted on a control panel?
Plug-type.
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What is the voltage/current range of a plug-type fuse?
150 volts at .5 to 30 amperes.
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What type of fuse is enclosed in a tube of insulation material with metal ferrules at each end?
A cartridge fuse.
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How are fuses rated?
By current, voltage, and time delay.
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When selecting a fuse for circuit protection (overload), the fuse should carry what current rating?
125% of normal circuit current.
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To protect a circuit from direct shorts, what fuse current rating should be used?
150% of normal circuit current.
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Fuses are rated with what three time delay ratings?
Delay, standard, and fast.
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What type of fuse time delay is activated when the current through the fuse is greater than the current rating of the fuse?
Delay.
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In what application can delay fuses be found?
Circuits with high surge or starting currents.
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What type of fuse has no built-in delay and are not fast acting?
A standard fuse.
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Fast acting fuses are used in what applications?
Used to protect devices that are very sensitive to increased current.
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What type of fuse would be used in an electrical power circuit?
A standard fuse.
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A fast acting fuse is designed to protect delicate instruments or what?
Semiconductors.
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What does the current rating of a fuse indicate?
The amount of current at which the fuse will open.
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The term voltage rating when associated with fuses means what?
The ability of the fuse to expeditiously extinguish the arc after the fuse element melts and the maximum voltage the open fuse will block.
-
When using the old military designation for fuses, a fuse marked FO2HR005B indicates what?
F=Fuse, O2=Style, H=500 volts, R005=.005 amperes, B=Delay.
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A fuse marked with a voltage code of G under the old military fuse designation would have what rating?
250 volts.
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Using the new military designation for fuses, a fuse marked FO2C500V5AS indicates what?
- F=Fuse, O2=Style, C=Fast, 500V=Maximum voltage, 5A=5 Ampere, S=SiIver plated.
- Fuse time delay ratings under the new military designation are identified in what way?
- By letters: A=Standard, B=Delay, C=Fast.
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What is the difference between old commercial fuse designation and new commercial fuse designation?
Lacks the style portion of coding with only letters being used in the new commercial fuse designation marking.
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What are two types of fuse holders?
Clip-type and post-type.
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What is the safest type of fuse holder?
Post-type.
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What is the simplest way to check for an open fuse?
Visual inspection.
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Severe pitting or burning of silver contacts on circuit breakers can be cleaned by what method?
By use of a fine file or fine sandpaper (No.OO).
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What is used to adjust voltage on a voltage regulator?
A voltage adjusting rheostat.
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What type of generator seldomly uses a voltage regulator?
A DC generator.
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What type of rectifier is used in the static exciter/electronic voltage regulator system?
Silicon controlled rectifier (SCR).
- Voltage regulators must be inspected visually at what periodicity?
- Weekly.
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Voltage regulators are designed to perform what two functions?
Maintain the generator terminal voltage within specified limits and provide for proper division of reactive current between generators operating in parallel.
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