Deck 19: Equipment and Conductor Short-Circuit

Question 1

____ 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 1

D

Question 2

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

Answer 2

B

Question 3

What is the conservative approach to conductor withstand ratings?

Answer 3

Because bare equipment grounding conductors are often installed in the same raceway or cable as the insulated circuit conductors, the weakest link of the system would be the insulation on the circuit conductors. Therefore, the conservative approach when considering conductor safe withstand ratings is to apply the 1 AMPERE-FOR 5 SECONDS-FOR EVERY 42.25 CIRCULAR MILS formula, or simply refer to a conductor short-circuit withstand rating chart .

Question 4

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

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

Question 5

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 6

What damage can occur to conductors under fault conditions?

Question 7

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

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

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

Question 10

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

Question 11

You can determine a conductor's short-time withstand rating using charts published by the ____.

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

Question 12

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

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

Question 13

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 14

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 15

A 75°C thermoplastic insulated Type THWN copper conductor can withstand 4200 amperes for one cycle. What is the I ² t 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

Question 16

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 17

Define an effective ground-fault current path.