Form Factors
A ground fault circuit interrupter circuit breaker (GFCI in USA and Canada) and residual-current breaker with overload (RCBO in Europe) are devices which combine the functions of a residual-current device with a circuit breaker. They detect both supply imbalance and overload current.
In Europe RCDs can fit on the same DIN rail as the MCBs, however the busbar arrangements in consumer units and distribution boards can make it awkward to use them in this way. If it is desired to protect an individual circuit an RCBO (Residual-current Circuit Breaker with Overcurrent protection) can be used. This incorporates an RCD and a miniature circuit breaker in one device.
Electrical plugs which incorporate an RCD are sometimes installed on appliances which might be considered to pose a particular safety hazard, for example long extension leads which might be used outdoors or garden equipment or hair dryers which may be used near a tub or sink. Occasionally an in-line RCD may be used to serve a similar function to one in a plug. By putting the RCD in the extension lead protection is provided at whatever outlet is used even if the building has old wiring, such as knob and tube, or wiring that does not contain a grounding conductor.
GFI receptacles can be used in cases where there is no grounding conductor, but must be labeled as "Ungrounded". An ungrounded GFI receptacle will trip using the built in Test button, but will not trip using a GFI test plug, because the plug tests by shorting a small current from line to the non existent ground.
Electrical sockets with included RCDs are becoming common.
Read more about this topic: Residual-current Device
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