Electrics keep tripping: RCD and breaker faults

Your consumer unit has two kinds of protective device.

• Circuit breakers (MCBs) protect one circuit against too much current. They trip if a circuit is overloaded or a cable shorts.
• RCDs watch for current leaking away to earth, which is what happens when someone gets a shock or water gets into a fitting. One RCD often covers half the circuits in the house.
• RCBOs do both jobs for a single circuit.

If the RCD trips, look for leakage: damp, a faulty appliance, an outside light. If a breaker trips, look for overload or a short: too many heaters on one circuit, or a damaged cable.

Switch off and unplug every appliance on the affected circuits. Reset the switch once. If it holds, plug appliances back in one at a time, waiting a minute between each. When it trips, the last thing you plugged in is the likely culprit. Kettles, washing machines, ovens and immersion heaters are common ones, because their heating elements start to leak current as they age.

If the switch trips with nothing plugged in, or will not reset at all, the fault is in the fixed wiring. Leave it off and book a visit. Do not keep resetting it, and do not tape the switch up.

Some causes are common across the capital. Rain gets into outside lights and garden sockets, which is why so many calls come after a downpour, particularly in boroughs with bigger gardens such as Bromley, where the Valuation Office Agency counts 14% of homes as detached.

In flats, a leak from above can track along cable runs and trip the lighting circuit. In 1930s semis in Harrow and Sutton, where 52% and 41% of homes date from between the wars, older sections of wiring often survive under floors and in lofts. When those homes get a new consumer unit with modern RCD protection, faults that were hidden for years can start tripping it. The RCD is not faulty: it is finding a problem the old fuse box could not see.

When the power keeps going, it is tempting to keep pushing the switch back up. Each reset sends current back into the fault. If the cause is a damaged cable or a burnt joint, that can make the damage worse or start a fire inside a wall.

A few things to avoid:

• Do not hold the switch up or tape it in place.
• Do not swap a trip switch for a bigger one, or fit a wire fuse of a higher rating in an old fuse box.
• Do not take the cover off the consumer unit.
• Do not run the fridge or freezer from an extension lead plugged into a different circuit through a window or under a door where it can get wet or trapped.

If the trip is only on one circuit and everything else works, leave that circuit off. That keeps the rest of the home running safely until the fault is found. If the main RCD keeps dropping and takes half the house with it, write down when it happens and what was switched on. That list often saves an hour of testing. Our posts on an RCD tripping at night and an electric shower that keeps tripping cover two of the most common patterns.