How to label your consumer unit so it is actually useful

What you need before you start

You need a way to see whether a circuit is live from a room away from the board, since you cannot watch the breaker and the socket at the same time. A cheap plug-in lamp or radio works for sockets; for ceiling lights you just watch whether they go out. A phone call with someone standing at the far end of the flat works as well as any tool if you live alone.

Get a torch, because you may be turning off the only light in a windowless bathroom or hallway. A pack of white label stickers or a label maker, a permanent marker, and masking tape and a pencil for a first draft are worth having before you begin, since you will want to rub out and rewrite more than once.

Check that every socket and switch in the flat is reachable and that nothing important is running unattended — no washing machine mid-cycle, no oven on, no one relying on the internet for a video call. Turning breakers off one at a time is safe, but it does interrupt things.

How to map out which breaker controls what

Turn on every light in the flat and plug the test lamp or radio into a socket in each room, or agree on a signal with whoever is helping. Go to the consumer unit and switch off breakers one at a time, waiting a few seconds after each before checking what has gone dark or silent. Write down what happened next to the breaker in pencil, then switch it back on before moving to the next one.

Work through the whole board this way, including anything unmarked. In Soviet-era panel flats one breaker often feeds several rooms at once because the original wiring was never split further, so do not assume one breaker means one room — note everything it affects. In a house, check whether outdoor sockets, a boiler, or underfloor heating manifolds each have their own breaker or share one with something else.

Do not forget the cooker, the water heater, and any breaker with no visible load — it may feed an outdoor light, a garage, or a neighbouring meter cupboard in an older building. If a breaker controls nothing you can find, leave a note to that effect rather than a blank label; a blank label gets ignored, a note gets investigated eventually.

Once you have a full pencil draft, go round a second time to check it, since it is easy to misread which light went out when two rooms are close together or open-plan.

What to write on the label so it is still useful in five years

Write what the circuit actually does, not just where it is: «Kitchen sockets — worktop and fridge» is more useful than «Kitchen», because a kitchen usually has more than one breaker. Include the cooker separately from kitchen sockets, and separate lighting circuits from socket circuits even when they are in the same room, since that split is common and worth recording.

Note anything unusual you found while mapping: a breaker feeding two rooms, an unlabelled spare, a circuit that also covers a hallway or landing light shared with a neighbour in an older building. Anyone opening the board later, including you in a few years, will thank you for the detail rather than a single word.

Use a label maker or neat block capitals in permanent marker, and stick the label next to the breaker rather than above the whole row, so there is no ambiguity about which one it refers to. Add the date you did the mapping in a corner of the board itself — wiring occasionally gets altered later, and a date tells the next person whether to trust the labels or redo the work.

• Room or area plus what it covers, not just the room name
• Cooker, water heater and underfloor heating labelled separately from general sockets
• Any breaker that feeds more than one room, written on both if it matters
• Spare or unidentified breakers marked as such rather than left blank
• Date the mapping was done, noted on the board

The mistake almost everyone makes

The common error is labelling by memory instead of by testing — writing «bedroom light» because that is what it probably is, based on position on the board or a guess from last time. Consumer units are not always wired in a logical left-to-right order matching the rooms, especially after any rewiring or an extension, so a label based on assumption is often wrong and worse than no label, because it is trusted.

The second common mistake is testing only sockets and forgetting fixed appliances — extractor fans, water heaters, underfloor heating pumps — which do not visibly react the way a lamp does. Check these by listening for a change or by feeling whether a pump or fan has stopped, rather than assuming they are covered by whichever socket circuit is nearby.

When to stop and call an electrician

Mapping and labelling a board you can already open safely is ordinary DIY. Stop and call a qualified electrician if a breaker trips the moment you switch it back on, if you find scorch marks, a smell of burning, or a breaker that feels warm, or if the board has no visible labelling scheme at all and wires disappear into a mess that has clearly been added to more than once without record.

If the consumer unit itself is old, has no residual current device, or is simply too small for the circuits it is trying to hold — common in flats that have had a kitchen or bathroom added to since the original wiring — labelling will not fix the underlying problem. In that case a full consumer unit replacement, from 350 € per job, is the more honest answer than another round of stickers.

For anything beyond mapping and labelling — adding a circuit, splitting an overloaded one, or replacing the board — our electrical work starts from 49 € per hour, with a fixed quote given in advance for larger jobs.