機電工程署的電業工程人員註冊制度

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.

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. 

These electrical wiring devices disconnect a circuit when it detects that the electric current is not balanced between the energized (line) conductor(s) and the return (neutral) conductor. 

Under normal circumstances, these two wires are expected to carry matching currents, and any difference usually indicates that a short circuit or other electrical anomaly is present. 

Even a small leakage current can mean a risk of harm or death due to electric shock if the leaking electric current passes through a human; a current of around 30 mA (0.030 amperes) is potentially sufficient to cause cardiac arrest or serious harm if it persists for more than a small fraction of a second. RCDs/RCCBs are designed to disconnect the conducting wires quickly enough to prevent serious injury from such shocks. (This is commonly described as the RCD/RCCB being "tripped".)

*******