Why does my RCD keep tripping?

What an RCD does

An RCD (residual current device) protects you from electric shock and reduces the risk of fire. It compares the current that goes out on a circuit with the current that comes back. If some current leaks to earth, it switches off in a fraction of a second.

So a trip usually means the RCD is doing its job. The question is where the leak comes from.

An RCD is different from a circuit breaker. A circuit breaker trips when a circuit carries too much current, for example from too many heaters on one circuit, or a short circuit. An RCBO does both jobs for one circuit.

Common causes

The most common cause is a faulty appliance. Other common causes are below.

• An appliance with a heating element, such as a kettle, washing machine, oven or immersion heater.
• Water in an outdoor socket, garden light or outbuilding supply, often after rain.
• A nail or screw through a cable, often after new shelves or flooring.
• Damp in old walls or in a cellar, which affects old cables and fittings.
• Many small leaks on one RCD, from many computers and chargers, that add up.
• A faulty RCD. This is less common than people think.

Safe checks you can do

You can do these checks without tools and without opening anything. Keep your hands dry. Do not remove the cover of the consumer unit.

Stop at once if you see scorch marks, smell burning or hear buzzing. Leave the power off and call an electrician.

• Unplug every appliance on the affected circuits. Switch off fixed items, such as an immersion heater or an outdoor light, at their own switch.
• Push the RCD switch back up. If it stays on, plug the appliances back in one at a time. Wait a few minutes between each.
• If it trips when one item goes back in, that item is probably faulty. Stop using it, and have it checked or replaced.
• If it still trips with everything unplugged, switch off all the circuit breakers under that RCD. Reset the RCD, then switch the breakers on one at a time.
• The breaker that makes the RCD trip shows the faulty circuit. Leave that breaker off and call an electrician.
• Write down what tripped, when, and the weather. This helps the electrician find faults that come and go.

When to call an electrician

Call an electrician if the RCD trips with nothing plugged in, or if one circuit makes it trip. These point to a fault in the fixed wiring. You must not try to repair the fixed wiring yourself.

Call an electrician the same day if a socket, switch or plug is hot or scorched, or if you got a shock or tingle. Also call if trips happen often at night or in wet weather and you cannot find the cause.

If your whole street is off, it is a power cut, not an RCD fault. Call 105.

Old boards and repeated trips

A new consumer unit with RCDs sometimes trips more than the old fuse box did. The new unit is not faulty. It finds leaks that the old fuses could not detect.

In older Cotswold homes, the electrician may find damp cable joints, old outdoor supplies or damaged cables under floors. They will repair these, or split circuits across more RCDs or RCBOs.

If your board has one RCD for the whole house, one fault switches off everything. Ask the electrician if RCBOs suit your home.

What it costs

Fault finding is usually charged by the hour, with a call-out fee for urgent visits. Ask each firm for its rates before it comes.

If the electrician advises a new consumer unit, see our consumer unit cost guide. If they find wider problems, our EICR cost guide and rewire cost guide explain those prices.

Questions

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