A residual-current device (RCD), or residual-current circuit breaker (RCCB),
is a device that instantly breaks an electric circuit to prevent
serious harm from an ongoing electric shock. Injury may still occur in
some cases, for example if a human falls after receiving a shock. In the
United States and Canada, the device is more commonly known as a ground fault circuit interrupter (GFCI), ground fault interrupter (GFI) or an appliance leakage current interrupter (ALCI). In the United Kingdom, these are better known by their initials RCD, and a combined RCD+MCB (miniature circuit breaker) is known as a RCBO (residual-current circuit breaker with overcurrent protection). In Australia, they are sometimes known as safety switches or an RCD. In Malta they are sometimes known as salvavita, from the Italian term. An earth leakage circuit breaker (ELCB) may be a residual-current device, although an older type of voltage-operated earth leakage circuit breaker also exists.
