TN LLE Fault Current and OCPD Ratings 2

Question 1

What does AIC stand for on a circuit breaker nameplate?

Accepted Answer

Ampere Interrupting Capacity

Answer

AIC stands for Ampere Interrupting Capacity, which is the maximum fault current the device can safely interrupt.

Question 2

Per NEC 110.9, what must the interrupting rating of equipment be sufficient to handle?

Accepted Answer

The available fault current at the line terminals

Answer

NEC 110.9 requires equipment to have an interrupting rating not less than the nominal circuit voltage and the current that is available at the line terminals.

Question 3

What is the typical available fault current at a residential 200A service panel?

Accepted Answer

10,000-22,000 amperes

Answer

Typical residential services see available fault currents of 10,000-22,000 amperes depending on transformer size and distance.

Question 4

What is the purpose of a current-limiting fuse?

Accepted Answer

To limit the peak let-through current to a value less than the available fault current

Answer

Current-limiting fuses operate fast enough to limit the peak fault current that passes through to a level significantly less than what would flow without the fuse.

Question 5

What happens if a circuit breaker with a 10,000 AIC rating is installed where the available fault current is 25,000 amperes?

Accepted Answer

The breaker may fail to interrupt the fault, potentially causing explosion, fire, or arc flash

Answer

An undersized interrupting rating means the breaker cannot safely clear the fault. The device may rupture, creating an arc flash or explosion.

TN LLE - Tennessee Limited Licensed Electrician Practice Test

TN LLE - Tennessee Limited Licensed Electrician Practice Test

TN LLE Fault Current and OCPD Ratings 2