RCD is a generic term which embraces the various forms such as RCCB, RCBO, etc. Residual Current Devices are now firmly established around the world as a primary means of providing protection against electrocution and fires caused by electrical faults. Less than one quarter of an amp (250mA) leaking from a faulty installation can generate sufficient heat to start a fire (the heating effect is proportional to the current squared), or if leaking through a human body for only 200mS can cause heart fibrillation and subsequent death.
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How an RCD Works 2016-08-23
Residual Current Devices (RCD) operating information