How quickly does a GFCI respond to a fault?

A Ground Fault Circuit Interrupter (GFCI) is designed to provide protection against electrical shock by detecting ground faults or leakage current in electrical circuits. The correct response time for a GFCI to react to a fault condition is indeed approximately 1/40th of a second.

This swift reaction time is crucial because it minimizes the risk of severe injuries or fatalities caused by electric shock. By de-energizing the circuit almost instantaneously upon detecting a fault—that is, when there is an imbalance between the outgoing and incoming current—a GFCI helps protect individuals from dangerous electrical exposure, particularly in wet or damp environments where the risk of shock is heightened.

This high-speed response is a core aspect of GFCI function, distinguishing it from standard circuit breakers, which typically have longer response times and do not provide the same level of protection against ground faults.