RCD keeps tripping: causes and what you can do yourself

An RCD (earth leakage circuit breaker) is the wide switch at the top of your fuse box with a test button on it. Its task is simple but vital: it measures whether all the current going into your installation also comes back out neatly. In a healthy installation those two are equal. If current leaks away to earth, for example via a broken appliance or via you when you touch something live, there is a difference.

As soon as that difference grows beyond around 30 milliamps, the RCD switches the power off within a fraction of a second. That 30 mA is deliberately low: it is the threshold below which a shock does not yet cause your heart lasting harm. So an RCD prevents a leaking appliance or a damaged wire from giving you a dangerous or fatal shock.

Important to remember: an RCD that trips is not a fault, but a warning. It steps in because current is leaking away somewhere. Bypassing or wedging an RCD that keeps tripping is therefore life-threatening. You remove the protection while the cause remains.

Your fuse box has two kinds of protection that are easy to mix up. The RCD protects people against leakage current to earth. The fuses or breakers (circuit breakers) protect the wiring against overload and short circuits: too many appliances on a circuit or a wire that shorts.

The distinction helps you track things down. If a single fuse or breaker trips, that one circuit is overloaded or something is shorting there. If the RCD trips, a whole row of circuits often goes at once, because an RCD usually sits in front of several circuits. That explains why an RCD fault sometimes leaves half your house dark while only one appliance is the cause.

Do you notice that it is a single fuse popping out and not the wide RCD? Then something else is going on. In our article about fuses that keep tripping you can read how to tackle that.

The most common culprit is moisture. An appliance that has got wet, an outdoor light or garden socket that has drawn moisture after a rain shower, or an old coffee machine with a damp heating element: it all causes a little escaping current. Often the RCD only trips once the appliance switches on or warms up.

Genuinely faulty appliances are a classic too. A water heater with a blown heating element, a washing machine or dishwasher where the element leaks, an old fridge or a broken lamp. The element is then partly in contact with the casing and leaks current to earth. You can usually pinpoint such appliances because the RCD trips at the moment they switch on or start a heating cycle.

Sometimes no single appliance is really broken, but everything together leaks just a bit too much. Each appliance leaks a tiny amount, and at a busy moment those small leakage currents tick together over the 30 mA. You see that more often in older installations with a single RCD for the whole house. And very occasionally the RCD itself is worn out or faulty. If your RCD is broken, it trips too early or for no clear reason. That last one you always have a professional confirm.

If the step-by-step plan does not let you pinpoint a circuit or appliance, the cause often lies in the fixed installation: a damaged wire in the wall, a damp junction box or a wiring fault. That is work for a certified electrician with the right measuring equipment.

Also call if the RCD will not go on at all, even with all circuits off. Then the RCD itself may be faulty, or there is an earth fault that intervenes directly. Do you smell burning or scorching near the fuse box, or feel a component getting hot? Then touch nothing and call straight away. That is an emergency.

And if the RCD keeps tripping for no identifiable reason, even though everything seems fine, have it checked rather than living with it. An RCD that trips at random is sometimes a sign of a smouldering problem in your installation. What you never do: wedge the switch in place or bypass it to be rid of the hassle. You are removing your only protection against electrocution.