Fault Current & OCPD Ratings Flashcards
6 cards from real TN LLE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Fault Current & OCPD Ratings flashcards as text
What does AIC stand for on a circuit breaker nameplate?
Answer: Ampere Interrupting Capacity
AIC stands for Ampere Interrupting Capacity, which is the maximum fault current the device can safely interrupt.
Per NEC 110.9, what must the interrupting rating of equipment be sufficient to handle?
Answer: The available fault current at the line terminals
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.
What is the typical available fault current at a residential 200A service panel?
Answer: 10,000-22,000 amperes
Typical residential services see available fault currents of 10,000-22,000 amperes depending on transformer size and distance.
What is the purpose of a current-limiting fuse?
Answer: To limit the peak let-through current to a value less than the available fault current
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.
What happens if a circuit breaker with a 10,000 AIC rating is installed where the available fault current is 25,000 amperes?
Answer: The breaker may fail to interrupt the fault, potentially causing explosion, fire, or arc flash
An undersized interrupting rating means the breaker cannot safely clear the fault. The device may rupture, creating an arc flash or explosion.
Per NEC 110.24, what marking is required on service equipment regarding fault current?
Answer: The maximum available fault current and date of calculation must be marked
NEC 110.24(A) requires service equipment (other than dwelling units) to be legibly marked with the maximum available fault current and the date the calculation was performed.