What is an RCD?

An RCD, or residual current device, is a life-saving device which is designed to prevent you from getting a fatal electric shock if you touch something live, such as a bare wire. It can also provide some protection against electrical fires. RCDs offer a level of personal protection that ordinary fuses and circuit-breakers cannot provide.

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An RCD is a sensitive safety device that switches off electricity automatically if there is a fault.

An RCD is designed to protect against the risks of electrocution and fire caused by earth faults.  For example, if you cut through the cable when mowing the lawn and accidentally touched the exposed live wires or a faulty appliance overheats causing electric current to flow to earth.

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Fault current could take various waveforms depending on the load characteristics.

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We now need to be installing type A RCD's when adding to or altering a circuit as technology has moved on many many items that we plug into our homes socket outlets have the ability to give a DC feedback onto the electrical system blinding the old and out of date type AC RCD's.

Type A 

In addition to the detection characteristics of type AC RCDs, Type A RCDs detect pulsating DC residual current. Such waveforms can be caused by diode or thyristor rectifier circuit in electronic loads. Type A RCD are specifically intended to be used for single phase class 1 electronic loads.