Deck 19: Equipment and Conductor Short-Circuit Protection

Question 1

The value of energy (heat) generated during a fault varies as the multiplied by the time (duration of fault) in seconds.

A)root-mean-square (RMS) current
B)square of the root-mean-square (RMS) current
C)root-mean-square (RMS) voltage
D)square of the root-mean-square (RMS) voltage

Answer 1

B

Question 2

forces acting upon electrical equipment (busbars, contacts, conductors, and so on) are proportional to the square of the PEAK current.

A)Electroweak
B)Gravitational
C)Nuclear
D)Magnetic

Answer 2

D

Question 3

A 75 degree Celsius thermoplastic insulated Type THW copper conductor can withstand 4200 amperes for one cycle.What is the I2t let-through value for a noncurrent-limiting circuit breaker that takes one cycle to open? The available fault current is 40,000 amperes.

A)3,200,000 ampere squared seconds
B)6,400,000 ampere squared seconds
C)12,800,000 ampere squared seconds
D)25,600,000 ampere squared seconds

Answer 3

D

Question 4

What impedance remains in the circuit under short-circuit or ground-fault conditions?

Question 5

Copper conductors can withstand one ampere (rms current) for seconds for every 42.25 circular mils (cm) of cross-sectional area.

A)three
B)five
C)seven
D)nine

Question 6

What is the conservative approach to conductor withstand ratings?

Question 7

In a short circuit, the conductors .

A)do not get hot
B)begin to get hot
C)get extremely hot and the insulation will melt off
D)stop the flow of current

Question 8

In an overloaded circuit, the conductors .

A)do not get hot
B)begin to get hot
C)get extremely hot
D)melt the insulation

Question 9

The term short-circuit current rating is synonymous with the term rating.

A)fuse
B)fault
C)withstand
D)breaker

Question 10

A 10 AWG copper conductor's withstand rating is ampere squared seconds.

A)60,516
B)121,032
C)302,580
D)605,160

Question 11

What are the requirements for bonding as they relate to electrical continuity?

Question 12

The interrupting rating is the at rated voltage that a device is intended to interrupt under standard test conditions.

A)highest current
B)lowest current
C)quickest ground fault
D)highest impedance

Question 13

A bare conductor can withstand higher levels of current than an insulated conductor of the same cross-sectional area.Do not exceed one ampere (rms current) for five seconds for every circular mils of cross-sectional area of the conductor.

A)29.1
B)42.3
C)54.2
D)61.8

Question 14

A common example of a tap is for fixture whips that connect a to a branch circuit.

A)luminaire
B)transformer
C)circuit breaker
D)smoke detector

Question 15

A conductor is defined in NEC 240.2 as a conductor, other than a service conductor, having overcurrent protection ahead of its point of supply that exceeds the value permitted for similar conductors that are not taps.

A)faulted
B)tap
C)magnetic
D)copper-like

Question 16

Branch-circuit conductors must have an ampacity not less than the served.

A)maximum load
B)minimum load
C)average load
D)average 3-phase load

Question 17

You can determine a conductor's short­time withstand rating using charts published by the .

A)ICEA
B)NEC
C)NFPA
D)UL

Question 18

The amount of heat generated in a conductor or other electrical equipment is a matter of how much current flows and ____.

A)the type of insulation
B)for how far
C)for how long
D)the OCPD

Question 19

What is the definition of an effective ground-fault current path?

Question 20

What damage can occur to conductors under fault conditions?