Why does my RCD keep tripping?

Quick answer

An RCD keeps tripping because something on the circuit is leaking current to earth. The usual causes are a faulty appliance, damp in an outside socket or light, a worn immersion heater or a washing machine on its way out. Unplug everything on that circuit, reset the RCD, then plug items back in one at a time.

Most trips are caused by an appliance, not the RCD
Damp outdoor sockets are a common Fylde coast cause
Unplug, reset, then reconnect one item at a time
Fault finding from £75 for the first hour

A tripping RCD is the single most common reason people ring us. It is also the fault a homeowner has the best chance of finding themselves, because nine times out of ten the cause is something plugged in, not something inside the walls. This guide walks through what an RCD is, the safe way to narrow the problem down, and the point at which you should stop and call an electrician.

What an RCD does

An RCD, short for residual current device, is a safety switch in your consumer unit (the fuse box). It measures the current going out along the live wire and the current coming back along the neutral. The two should match. If some goes missing, because it is leaking to earth through a damp fitting, a damaged cable or a person, the RCD switches off in a fraction of a second. The standard household RCD trips at 30 milliamps, which is far below the level that would stop a heart.

That is why an RCD tripping is, in a sense, good news. It has done its job. An old fuse box with no RCD would have let the fault carry on until something got hot. The frustration comes when it trips over and over and you cannot see why.

Modern consumer units often use RCBOs instead, one per circuit, which are a breaker and an RCD combined. Older units have one or two RCDs that each cover several circuits. If yours is the older type, one faulty kettle can take out half the house, which is a clue in itself.

Common causes

A faulty appliance. The most common cause by far. Kettles, washing machines, dishwashers, tumble dryers, immersion heaters, fridge freezers and ovens all have heating elements or motors that can leak current as they age. A kettle element with a hairline crack will trip the RCD the moment it is switched on.

Moisture outdoors. Outdoor sockets, garden lights, pond pumps, shed supplies and hot tubs live in the weather. Water gets into a fitting, or a seal fails, and the RCD sees the leak. We see this constantly along the Promenade and on South Shore after a wet, windy night.

Damaged cable. A nail through a cable behind plasterboard, a mouse that has chewed a flex under the floor, a cable nicked by a spade in the garden. These cause trips that feel random because they depend on damp and movement.

Too much on one RCD. Every appliance leaks a tiny amount of current even when healthy. On an older unit where one RCD covers most of the house, a dozen healthy appliances can add up to enough to trip it. The fix is usually a consumer unit with RCBOs, not chasing a fault that is not there.

Nuisance tripping. Some things, such as older fluorescent lights and some electric showers, cause brief surges that an RCD can misread. If it only trips when one particular thing switches on, that is your suspect.

The safe unplug-and-reset test

This is the part you can do yourself. It involves nothing more than unplugging things and flicking switches. Do not remove any covers.

Go to the consumer unit and look at which switch has dropped. The RCD is the wider switch, often with a test button marked T next to it. Note which circuits it covers if they are labelled.
Switch off every appliance on those circuits at the socket, and unplug everything you can reach: kitchen appliances, the washing machine, chargers, lamps, the lot. Anything wired in, like a cooker or immersion heater, switch off at its own wall switch.
Reset the RCD. Push it firmly to the on position. If it stays on, the fault is in something you just unplugged. If it will not reset with everything unplugged, skip to the next section and stop.
Plug things back in one at a time, switching each one on and giving it a minute. When the RCD trips, the last thing you plugged in is the culprit. Leave it unplugged.
If nothing trips, plug everything back in and carry on. A damp appliance can dry out and clear itself for a while. Note the date and what the weather was doing.

If the RCD trips the instant you switch on a particular appliance, every time, stop using it. A kettle or toaster is cheaper to replace than to repair; a washing machine or oven may be worth a repair engineer’s visit.

When it trips at random

Random is usually weather. On the Fylde coast we get wind-driven rain that finds its way into fittings that would be fine inland. Outdoor sockets whose lids have cracked, garden light fittings facing the sea, shed and garage supplies with a dodgy joint, and the back of a 1930s semi where the kitchen extension cable runs through a damp wall. The RCD trips at two in the morning after a storm, you reset it in the morning, and it holds for a fortnight until the next one.

The first thing to try is to switch off and unplug everything outdoors: garden lighting, the pond pump, the socket on the patio, the hot tub at its isolator. If the trips stop, you have your area. Outdoor circuits can usually be separated so that a damp garden light no longer takes out the fridge.

Old chest freezers in cold, damp garages are the other repeat offender; the leak builds slowly until the RCD catches it at random.

When to stop and call someone

Some things are not a homeowner job, and an RCD is sometimes telling you about a problem that needs tools and a meter to find. Stop and get an electrician if:

The RCD will not reset even with everything unplugged and switched off.
You can smell burning, or a socket, switch or the consumer unit itself is warm or discoloured.
The RCD trips with nothing plugged in on that circuit, which points to the fixed wiring.
It trips when you use the shower or the cooker and those are wired in, not plugged in.
You have a lighting circuit tripping, since there is nothing to unplug and the fault is in a fitting or cable.
You have narrowed it to an outdoor circuit and the fittings look damaged.
There has been a flood, a leak from upstairs, or building work in the house recently.

If the power is off to the fridge or a freezer and you cannot get it back, say so when you ring. We treat food in a freezer as the clock running.

Our fault finding service is £75 including VAT for the first hour and £55 for each hour after that. Most faults are found within the first hour, especially if you have already done the unplug test and can tell us what you found. If a damp outdoor fitting is the cause, we can usually replace it on the same visit.

Testing your RCD

Every RCD has a test button, marked T or Test. Pressing it creates a small, deliberate leak and the RCD should trip immediately. Reset it and you are done. The label on your consumer unit says to test quarterly, so four times a year, and that is the figure we give customers. In practice most people do it when the clocks change, which is twice a year and better than never.

If you press the button and nothing happens, the RCD may have stuck. That is a call-us situation, because a stuck RCD gives no protection at all and you would never know until something went wrong. Do not keep pressing it.

The button only proves the mechanism works, not how fast it trips or at what current. That needs instruments, and it is part of every electrical installation condition report, an EICR, that we do.

Need a hand?

If the unplug test did not find it, or you would rather we did it, our fault finding page explains how a visit works and what it costs. Get in touch through the contact page and tell us what the RCD does and when; it helps us turn up with the right parts.