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 or if leakage through a human body for only 200mS can cause heart fibrillation and subsequent death.
PRINCIPLE OF RCD OPERATION:
An RCD protects by constantly monitoring the current flowing in the live and neutral wires supplying a circuit or individual item of equipment. Under normal circumstances, the current flowing in the two wires is equal. When an earth leakage occurs due to a fault in the circuit or an accident with the equipment, an imbalance occurs and this is detected by the RCD, which automatically cuts off the power before injury or damage can result. To be effective, the RCD must operate very quickly at a low earth leakage current. Those designed to protect human life are engineered to trip out with an earth leakage current of 30mA within 200mS and at a higher earth current of 150mA, they will trip in less than 40mS. These limits are well inside the safety zone, within electrocution or fire would not be expected to occur.
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