Residual-Current Device

A residual-current device, also called a residual-current circuit breaker or, in North America, a ground fault circuit interrupter, is a safety device that watches for an imbalance between the current flowing into a circuit on its line conductor and the current flowing back out on its neutral conductor. Under normal operation the two currents match; if some current is instead leaking away through an unintended path, such as through a person to earth, the device detects that imbalance and disconnects the circuit. It is built to react to very small leakage currents, on the order of 5 to 30 milliamps, and to trip in well under 30 milliseconds, because alternating current above about 20 milliamps passing through a human body can be enough to cause cardiac arrest. The device is built to reduce the severity of injury from electric shock, rather than to protect wiring or equipment from overload, which is the job of an ordinary circuit breaker or fuse. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/