Which trip type is intended for very high fault current conditions causing the circuit breaker to open without an intentional delay, with fixed or adjustable pickup?

• A. Energy-reducing maintenance switching trip (A)
• B. Long-time trip (L)
• C. Instantaneous trip (I)
• D. Short-time trip (S)

Answer: (C)

Instantaneous trip is designed to clear very high fault currents with no intentional delay. When the current exceeds the instantaneous pickup setting, the breaker trips immediately to interrupt the fault, protecting equipment from rapid, high-energy damage.

Long-time trips are for overloads and include a time delay, which isn’t appropriate for severe faults that must be cleared right away. Short-time trips do have a brief delay to tolerate transient overloads, but they aren’t truly instantaneous. The energy-reducing maintenance switching trip is used during maintenance to limit energy or enable safe service, not for rapid fault clearance.