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A residual-current device (RCD), residual-current circuit breaker (RCCB) or ground fault circuit interrupter (GFCI) [a] is an electrical safety device, more specifically a form of Earth-leakage protection device, that interrupts an electrical circuit when the current passing through a conductor is not equal and opposite in both directions, therefore indicating leakage current to ground or ...
Such devices may be found in the form of either a circuit breaker, known as an earth-leakage circuit breaker (ELCB), or built into a socket (aka receptacle). Voltage-operated ELCBs can still be found in the wild, though these largely fell out of favour after the invention of the current-sensing based RCD (aka GFCI) technology.
A GCM or ground continuity monitor (also called a ground integrity monitor or ground continuity tester) is an electrical safety device that monitors the impedance to ground of a temporary electrical circuit and can provide indication (or protective trip) in the event impedance rises to an unsafe value. A GCM is either an external testing device ...
A ground fault protection relay must trip the breaker to protect the circuit before overheating of the resistor occurs. High-resistance grounding (HRG) systems use an NGR to limit the fault current to 25 A or less. They have a continuous rating, and are designed to operate with a single-ground fault.
Incorrectly configured or old model reclosers have been implicated in the starting or spread of wildfires. Research into the Australian 2009 Black Saturday Bushfires indicated that reclosers operating as single shot circuit breakers with Sensitive Ground Fault protection configured at 500mA would reduce fire start risk by 80%.
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If the fault path between exposed conductive parts and the supply has sufficiently low impedance, then should such a part accidentally become energized, the fault current will cause the circuit overcurrent protection device (fuse or circuit breaker) to open, clearing the fault.
A ground conductor only carries significant current if there is a circuit fault that would otherwise energize exposed conductive parts and present a shock hazard. In that case, circuit protection devices may detect a fault to a grounded metal enclosure and automatically de-energize the circuit, or may provide a warning of a ground fault.