residual-current device

A residual-current device (RCD), residual-current circuit breaker (RCCB) or ground fault circuit interrupter (GFCI) is an electrical safety device, more specifically a form of Earth-leakage circuit breaker, that interrupts an electrical circuit when the current passing through line and neutral conductors of a circuit is not equal (the term residual relating to the imbalance), therefore indicating current leaking to ground, or to an unintended path that bypasses the protective device. The device's purpose is to reduce the severity of injury caused by an electric shock. This type of circuit interrupter cannot protect a person who touches both circuit conductors at the same time, since it then cannot distinguish normal current from that passing through a person.

A residual-current circuit breaker with integrated overcurrent protection (RCBO) combines RCD protection with additional overcurrent protection into the same device.