There are five common overcurrent protection trip types for circuit breakers. Which type is intended for overcurrents that can persist for many seconds to minutes and is considered overload and low-level fault protection?

• A. Instantaneous trip (I)
• B. Short-time trip (S)
• C. Ground-fault trip
• D. Long-time trip (L)

Answer: (D)

Overcurrent protection uses different time-delayed responses to match how faults behave. For currents that are only moderately higher than normal and can persist for a while, you want a delay so temporary spikes don’t trip the circuit. The long-time trip is designed for just that: it has a delay that allows many seconds to minutes of sustained overloads to pass before it trips, providing overload and low-level fault protection without reacting to brief fluctuations.

Instantaneous trips trigger immediately for high fault currents, which is good for severe faults but not for longer-lasting but milder overloads. Short-time trips delay only briefly to cover faults that last a short duration. Ground-fault trips respond to leakage to earth, not to excessive line current.

So, the function intended for overloads that can persist for many seconds to minutes is the long-time trip.