How do I read my consumer unit?

The consumer unit is the one part of the electrical installation you are expected to operate, and most households have never been told what any of it means.

Safety

What you'll need

• A torch
• A pen and label strips, or a phone camera
• A helper to confirm what goes off

Step by step

1. Find it and make sure you can reach it.Usually under the stairs, in a hall cupboard or near the meter. Everyone in the household should know where it is and be able to get to it in the dark without moving anything.
2. Never take the cover off.The incoming tails from the meter are live regardless of every switch position, and they are not protected by anything. The face of the unit is all you need.
3. Identify the main switch.The largest switch, usually at one end and often red. It isolates the whole installation and is what you use in an emergency or before any work.
4. Identify the RCDs.The ones with a small test button, usually marked T or Test. An RCD detects current leaking to earth — through a person, for example — and disconnects in milliseconds. It protects people rather than cables.
5. Identify the MCBs.The smaller switches, each with a number such as 6, 16, 32 or 40. That is the rating in amps and it tells you what the circuit is: 6A lighting, 16A immersion, 32A ring final for sockets, 40A or 45A cooker or shower.
6. Look for RCBOs.In newer units each circuit may have a combined device with its own test button, doing both jobs. That is better, because a fault trips only the affected circuit rather than half the house.
7. Read the existing labels sceptically.Labels are often wrong, especially after any alteration. Treat them as a starting point rather than as fact.
8. Map it properly, one circuit at a time.Switch one MCB off, walk the house with a helper and note what has gone off. Repeat. It takes half an hour once and saves time at every future fault.
9. Write the map somewhere permanent.Labels on the unit itself, plus a photograph on your phone. In an emergency you want to find the right breaker immediately.
10. Test the RCDs quarterly.Press the test button. It should trip instantly. Reset it afterwards, and check the fridge and any timers came back on. An RCD that does not trip is a serious fault.
11. Know the difference when something trips.A single MCB means a fault on that circuit, usually an appliance. An RCD taking out several circuits means earth leakage somewhere, and the way to find it is to switch everything off and reintroduce circuits one at a time.
12. Recognise an old fuse board.Rewireable fuses with fuse wire, or a wooden back, means the installation is old and almost certainly has no RCD protection. That is worth an electrician's assessment.
13. Look for the installation certificate.Often a sticker inside the door or a card nearby, giving the date of the last inspection. An EICR is generally recommended every ten years for an owner-occupied home, five for rented.
14. Never force a breaker that will not stay on.It is holding open because there is a fault. Repeatedly resetting it does not fix anything and can cause damage.

Tips

• Never remove the cover. The incoming tails stay live no matter what you switch off.
• Map the circuits once, properly. Existing labels are frequently wrong.
• Press the RCD test buttons quarterly. It takes a minute and it is a safety device that can fail silently.

Common mistakes

• Repeatedly resetting a breaker that keeps tripping — It is doing its job — there is a fault on that circuit. Forcing it back on risks damage and, with a genuine fault, a fire.
• Trusting the existing labels — They are often original, often generic, and frequently wrong after any alteration. Mapping the circuits yourself is the only reliable version.

If it doesn't work

Questions people ask