- Before answering this, we need to be clear whether or not you have rewireable fuses like these... MCBs and RCDs, but some people still refer to them as fuses.
- Someone may have drilled a hole in a wall and has accidentally drilled into a concealed electric cable.
- A light fitting or socket outlet has just been replaced, and a short circuit between live conductors and earth has occurred. This can sometimes happen when a screw for socket face place is tightened and happens to trap and penetrate one of the live wires behind the face plate.
- An appliance no longer works properly or has stopped working completely. The fault could be an internal short circuit which causes the RCD protecting that circuit to trip.
Moisture due to steam, such as with an iron or sandwich maker, can be a cause of this, as can a loose wire. A recent example I needed to diagnose turned out to be an earth wire had come loose in an immersion heater and was touching the neutral wire.
- Rain has found its way into an outside light or socket, or an external junction box or enclosure has been used which is not sufficiently weatherproof and has allowed moisture in. If this happens, a short circuit is highly likely.
- Note that when having lights or sockets installed outside or in other places where moisture can occur, the fittings should have a suitable IP Rating, which describes item's level of resistant to water, splashes, etc.
- I have provided more information on a separate page about IP Ratings.
- When you look at the consumer unit (what many people still call the fuse board), it should be clear through labelling which circuits the RCD protects. There may be one or several circuits.
- Before resetting the RCD, switch off the MCB (mini circuit breaker) for each circuit which is protected by the RCD which keeps tripping.
- Once you have done that, push the paddle on the RCD up to the ON position.
DO NOT press the test button whilst doing this. Some people incorrectly think that the test button needs to be pushed in whilst the switch paddle is moved to the ON position, but this will cause the RCD to trip.
- In theory, the RCD should remain in the ON position as none of the circuits it is protecting are energised. If it does not remain on, try again, making sure that you are NOT pressing the test button by mistake.
- If it still doesn't remain on, the problem will need to be investigated further by an electrician.
- Assuming that the RCD has remained ON, then switch each of the circuits which are protected by the RCD on one at a time, waiting a couple of seconds between each one.
- If one of the circuits causes the RCD to trip, you can leave that one off and allow the other circuits to stay on and be used. The circuit with the fault will need to be investigated by an electrician.
- If all of the circuits can be switched on without causing the RCD to trip, that's good news. But if you then find that switching on a specific appliance causes the RCD to trip again, avoid using that appliance and either seek to replace it or have it repaired.
- If nuisance tripping still occurs, call an electrician.
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