Residual Current Device (See wiki)
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. An injury may still occur in some cases, for example, if a human falls after receiving a shock, or if the person touches both conductors at the same time.
RCD is the name used in the United Kingdom. In the United States and Canada, the terms ground fault circuit interrupter (GFCI), ground fault interrupter (GFI) or appliance leakage current interrupter (ALCI) are used. If the RCD device has additionally overcurrent protection integrated in the same device, it is referred to as RCBO (Residual Current Circuit Breaker with Overcurrent Protection. Suppose it really should be RCCBOP)).
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.