Why does my trip switch keep going off?

Telling an RCD trip from a breaker trip, the socket-by-socket method that finds the faulty appliance, and when to stop and call someone.

Difficulty: beginner
Time: 30 min
Read: 4 min
Safety: restricted

Short answer

Work out which device tripped. A single breaker means a circuit is overloaded or has a fault; an RCD means current is leaking to earth, usually from one appliance. Unplug everything on the affected circuit, reset, then reconnect one item at a time until it trips again.

A tripping switch is a protective device operating correctly, which is worth remembering before being annoyed by it. The diagnosis is methodical rather than technical, and it usually ends at one appliance.

Safety

A trip switch is doing its job — it has detected something dangerous. Resetting it is fine; resetting it repeatedly without finding the cause is not. Never remove a consumer unit cover, work on fixed wiring, or bypass a device. If a trip will not stay on, or trips immediately with everything unplugged, stop and call a registered electrician. If anyone has had a shock, or there is a burning smell or scorching, turn the supply off at the main switch and call an electrician the same day.

Step by step

Look at the consumer unit and see what actually moved.A single small switch down is a circuit breaker — overload or a fault on that circuit. A larger switch marked RCD or RCBO, taking several circuits with it, means earth leakage. They point at different causes.
Note which circuits went off.Walk round and see what has lost power. Consumer units are usually labelled, though often inaccurately. This tells you which appliances to suspect.
Unplug everything on the affected circuit.Everything, including things you are sure are fine — chargers, extension leads, the fridge, anything in an outbuilding. Then reset the switch.
If it now stays on, reconnect one item at a time.Plug in and switch on one appliance, wait a minute, then the next. The one that trips it is your fault. This is slow and it is the method that works.
Suspect the usual culprits first.Kettles, toasters, washing machines, tumble dryers, immersion heaters, outdoor lights and anything with a heating element or exposed to damp. Water and heating elements cause most earth-leakage trips.
Think about overload separately.If a breaker trips only when several high-power things run together — kettle, microwave, heater — that is overload rather than a fault. Spread the load across circuits.
Check outdoor and garage circuits after rain.Water in an outside socket, a garden light or a pond pump is a classic intermittent RCD trip that follows the weather.
Consider cumulative leakage if nothing single is at fault.Many appliances leak a tiny amount to earth legitimately. Enough of them on one RCD adds up to a trip with no single culprit. An electrician can split the circuits.
Stop if it will not reset with everything unplugged.That points at the fixed wiring, a light fitting, or the consumer unit itself. None of those is a DIY job. Call a registered electrician.
Test the RCD every few months.Press the test button on the RCD. It should trip immediately. If it does not, it is not protecting anything and needs replacing.

Tips

Do the unplug-and-reconnect test with a torch to hand. It is easier in daylight, and much easier if you have not just lost the lighting circuit too.
Label the consumer unit properly while you are working out which circuit is which. It saves an hour next time.
An appliance that trips the RCD only when it heats up is still faulty. Intermittent does not mean minor.

Common mistakes

Resetting repeatedly without investigating — The device is detecting a genuine fault — commonly current finding a path to earth, which is the path that goes through a person.
Reconnecting everything at once after a successful reset — You learn nothing, and you are back where you started at the next trip. One item at a time is the whole method.

If it doesn't work

RCD trips when the washing machine reaches heating

Cause: Failing heating element leaking to earth — Fix: Stop using it and have the element tested or replaced. Elements fail this way routinely.

Breaker trips only when the kettle and microwave run together

Cause: Circuit overload rather than a fault — Fix: Use them on different circuits, or not simultaneously. If the circuit is genuinely undersized for the room, that is an electrician's job.

Trips after heavy rain

Cause: Water in an outdoor socket, light or pump — Fix: Isolate outdoor circuits and dry them out. Have outdoor fittings checked for proper weatherproofing.

Will not reset even with everything unplugged

Cause: Fault in the fixed wiring, a light fitting, or the unit itself — Fix: Leave it off and call a registered electrician. Do not remove any cover.

Questions people ask

Why does my RCD keep tripping?

It has detected current leaking to earth, almost always from one appliance — commonly something with a heating element or exposed to damp. Unplug everything on the circuit, reset, and reconnect one item at a time.

Is it safe to keep resetting a trip switch?

Resetting once to see whether it recurs is reasonable. Resetting repeatedly without finding the cause is not — the device is detecting a real fault, and if it will not reset with everything unplugged you need an electrician.