What is interrupting capacity?

• A. The maximum operating current
• B. The current at which it trips
• C. The current rating at normal operation
• D. The amount of fault current a breaker can interrupt without taking damage to itself

Answer: (D)

Interrupting capacity is the maximum fault current a circuit breaker can interrupt and still open without being damaged. It describes the breaker’s ability to withstand the energy of a short-circuit while properly tripping to clear the fault. This matters because the actual fault current can be many times higher than normal operating current, and a breaker must survive that event to protect the system. If the fault current exceeds this capacity, the breaker may fail or fail to trip, risking equipment damage or fire. The other terms refer to different ratings: the continuous operating current is what the breaker can carry under normal conditions, and the current at which it trips is the threshold that triggers opening, not how much fault current it can interrupt safely.