A
residual-current device (
RCD), or
residual-current circuit breaker (
RCCB), is a device to quickly disconnect current 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 is known as a
RCBO (
residual-current circuit breaker with overcurrent protection). In
Australia, they are sometimes known as
safety switches or a
RCD. 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. In German speaking countries the device is sometimes known as
FI where the
F stands for fault (Fehler) and
I for the symbol that represents
Electric current.