Why does my RCD keep tripping?

Glossary · Consumer units and protection

What causes it

An RCD trips when it detects current leaking to earth. Electrical Safety First says that if the RCD in your fuse box keeps tripping, there is likely a fault that needs investigating, either with a particular appliance or with the wiring itself.^{[2]Electrical Safety First, FAQ for electrical safety: your questions answered}

The IET gives the same picture. A tripped protective device is likely to be a fault with an appliance connected to the installation, not the installation. Faults on the installation can still happen, and they are more likely after DIY such as hanging pictures or shelves.^{[1]IET, Consumer units: safe fuse-box upgrades for modern homes} On a lighting circuit, the IET also names a blown or failed lamp as a possible cause, mostly with older tungsten bulbs.^{[1]IET, Consumer units: safe fuse-box upgrades for modern homes}

So the usual suspects are:

• a faulty appliance plugged into a socket on that circuit
• damage to a cable or a wiring accessory during DIY, for example hanging pictures or shelves
• a failed lamp on a lighting circuit
• a fault in the fixed wiring, which only testing will find

What you can check yourself

The IET describes one fault-finding routine for a householder. It uses nothing but plugs and the reset switch.^{[1]IET, Consumer units: safe fuse-box upgrades for modern homes}

1. Unplug every appliance on the affected circuit. Take the plug fully out of the socket. Turning the appliance off at the socket is not enough.
2. Reset the tripped device.
3. If it stays on, plug the appliances back in one at a time.
4. The one that trips the device again is the faulty item. Do not use it until it has been repaired.

The IET also says resetting a device again and again on a fault could damage it, so keep the number of attempts to a minimum.^{[1]IET, Consumer units: safe fuse-box upgrades for modern homes}

You can also check that the RCD itself works. Press the button marked T or Test. The device should switch off. If it does not, get a registered electrician. The IET says to do this test every six months.^{[3]IET, BS 7671 FAQs: Consumer Units and Protective Devices} The RCD trip test page explains it in more detail.

When to call an engineer

Call a registered electrician if any of these apply:

• The device will not reset with every appliance unplugged.
• The same device trips again after you have removed a suspect appliance.
• You think DIY work may have damaged a cable.
• The test button does not switch the RCD off.

The IET says that where a device will not reset with everything unplugged, a registered contractor can test the installation and diagnose the fault.^{[1]IET, Consumer units: safe fuse-box upgrades for modern homes} Electrical Safety First also says to have a registered electrician investigate a tripping RCD or a test button that fails.^{[2]Electrical Safety First, FAQ for electrical safety: your questions answered}

If you notice a burning smell, excessive heat, smoke, or burning or charring, the IET says the installation should be isolated immediately and a registered electrical contractor consulted.^{[1]IET, Consumer units: safe fuse-box upgrades for modern homes} See burning smell from a socket for more on that. For a fault you cannot leave until morning, Martin Day Electricians has an emergency electrician service in Leeds.

Example

Dan hears the RCD click off every time his wife runs the tumble dryer in the utility room. He unplugs everything on the circuit, resets the RCD once, and it stays on. He plugs the freezer back in, then the washing machine. Both are fine.

When the tumble dryer goes back in, the RCD trips again. Dan leaves the dryer unplugged and does not use it. If the RCD had tripped with everything unplugged, he would have called a registered electrician instead.

What people get wrong

The common mistake is to keep resetting the switch until it holds. A tripping RCD is a warning that something is leaking to earth. Resetting it over and over can damage the device and does nothing about the fault.

The other mistake is to blame the RCD. It is the part of the installation that is working. Replacing it without finding the fault does not make the fault go away, and that work is for a registered electrician.

The bottom line

An RCD that keeps tripping is reacting to a fault, most often in an appliance but sometimes in the wiring. You can unplug everything, reset once and add appliances back one at a time to find a faulty item. If it will not reset, or you smell burning, stop and call a registered electrician.