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RCDs - Just what are they?


RCDs (Residual Current Devices) are electrical safety switches that remove the supply to an electrical circuit when the circuit is unsafe; if an RCD 'trips' it has tripped for a reason, the problem is rarely a faulty RCD.

Many electrical problems are 'momentary' – they only exist for a fraction of a second. RCDs, rightly, 'err on the side of safety' and will trip when the circuit is momentarily unsafe. Once the 'moment' has passed it is possible to 'reset the RCD' and restore power to the circuit.

If the circuit is unsafe for more than a moment the RCD will trip again when it is reset; there are some basic actions the homeowner can follow to fix this. If the 'basic actions' below do not stop the RCD tripping the homeowner should call a qualified electrician.

Where can I find my RCD?

The RCD (shown below) will usually be in an RCD 'domestic unit' (shown below). The RCD domestic unit will contain about 10 RCDs. The RCD domestic unit will usually be in an 'out of the way' place, for instance next to the electricity meter, at the back of a kitchen unit, in an airing cupboard, the cupboard under the stairs.

RCD
RCD
RCD Comsumer Unit
RCD Consumer Unit

The RCD and RCD domestic unit may not quite look the same as these ones but will be similar.

The RCD will be about 2 inches (5cm) by 1 inch (2.5cm) and will have a 'standard' toggle switch (the 'main' switch) and a push-button 'push-button' (test) switch. The RCD domestic unit will have thick (large diameter) cable going into it – this cable is the 'main ring' cable.

 

Reset RCDHow To Reset An RCD

  • To reset an RCD move the main toggle switch to the other position; if down move up, if up move it to the down position.
  • Look at the RCDs.
  • Is one main toggle switch in a different position to the rest? Is one main toggle switch up and the other RCD main toggle switches down or down when the rest are up?
  • If one RCD main toggle switch is in a different position to the rest move it to the same position. Moving the main toggle switch is called 'resetting the RCD'. If the RCD stays reset, the main toggle switch does not go back to the other position, the problem is solved.
  • If the RCD does go back to the other position this is called 'a constantly tripping' RCD – see below.
  • Homeowners should be aware that some RCD domestic units have there own 'trip switches', some domestic units have there own isolation switches (on\off switches).
  • These switches may be standard 'toggle' type or 'push button' type. Are the domestic unit switches in the correct position?
RCD

NAPIT is an organisation committed to consumer safety in the Domestic, Commercial and Industrial sectors. The whole aim of the organisation is to ensure that through the competence of our Members, consumers can be confident of work that complies with the relevant regulations. When you see the Napit logo you know you have found a tradesperson in your area that you can rely on. OUR REGISTERED NUMBER IS: 12540 - Part P Registered Electricians

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