Consumer unit replacement

A fuse box and a consumer unit do the same job. They take the supply from the meter and split it into circuits, such as the lights, the sockets and the cooker, each with its own protective device. The difference is what that protection can do.

An older fuse box uses rewirable fuses: a carrier with a length of fuse wire across it that melts if too much current flows. That protects the cable from overload, and nothing else. It cannot tell when current is leaking to earth, which is what happens when someone touches something live. And a fuse rewired with the wrong wire gives no reliable protection at all.

A modern consumer unit uses circuit breakers, which trip instead of melting, and residual current protection. Plenty of houses round here still have the board they were built with. The Sandhurst estates went up from the late 1950s to the 1980s and most of Bracknell between the 1950s and the 1970s, when rewirable fuses were normal.

An RCD compares the current going out on the line conductor with the current coming back on the neutral. If they differ, some is leaking to earth, possibly through a person, and the RCD disconnects in a fraction of a second. Modern regulations require 30 mA RCD protection for most circuits in a home, including the sockets. A rewirable fuse box gives none.

Older boards often put several circuits behind one RCD, so a fault on one of them switches off the lot and you are left looking for a torch. An RCBO combines a circuit breaker and an RCD in one device for a single circuit. A fault on the kitchen sockets trips the kitchen sockets, and the lights stay on.

Which arrangement suits your house is set out in the quote, with the reasons.

A surge protection device (SPD) diverts short spikes in voltage, from lightning or from switching on the network, away from the wiring and whatever is plugged into it. One is now normally fitted with a new board.

Since 2016, new consumer units in homes have had to be in a non-combustible enclosure, which in practice means steel. A plastic board fitted before then is not automatically unsafe, but its replacement will be steel.

Arc fault detection devices (AFDDs) are also available. They watch for the electrical signature of arcing in a damaged cable or a loose connection. For an ordinary house they are an option, not a requirement, and we can talk through whether one is worth it for yours.

Age on its own does not decide it. These do:

• Rewirable fuses: carriers that pull out, with wire across them.
• No RCD: no device on the board with a test button marked T or Test.
• Fuses that blow, or breakers that trip, more than once in a while.
• A board that is warm to the touch, buzzes, or has scorch marks on it.
• A new circuit on the way, for an EV charger, a kitchen or an extension, and nowhere safe to connect it.
• You are buying or selling, or nobody can remember the last inspection.

If you are not sure what you have, send a photo of the board on WhatsApp and we will tell you. If the wiring itself looks old, with round-pin sockets or black rubber or fabric-covered flex, an inspection and test (EICR) first is the honest answer: a new board does not fix old cable, and a rewire may be the bigger job to plan for.

1. Test before anything is disconnected. RCD protection is less forgiving than a fuse. A circuit with poor insulation, or a neutral shared with another circuit, will trip it. Better to find that first.
2. Power off, old board out. The new board goes up and the meter tails and main earth are connected.
3. Circuits connected and labelled. Each one goes to its own protective device and gets its line on the circuit chart.
4. Earthing and bonding checked. If the bonding to the gas and water pipes is missing or undersized, it is normally put right as part of the job, and the quote says so.
5. Every circuit tested, power back on. Then we show you round the new board.

The power has to be off while the board is changed, so keep the fridge and freezer closed and charge your phone the night before. We agree the day with you in advance.

Testing is what makes the job finished. Each circuit is tested for continuity, insulation resistance, polarity and earth fault loop impedance, and every RCD or RCBO is tested to confirm it disconnects as it should.

The results go on an Electrical Installation Certificate (EIC). It records what was installed, how it was tested and what the readings were, and it gives a recommended date for the next inspection. Work is to BS 7671, the IET Wiring Regulations.

Replacing a consumer unit is notifiable work under Part P of the Building Regulations. A registered installer self-certifies the work and makes the notification to building control for you, and you receive a Building Regulations compliance certificate.

Locally, building control sits with the council: Bracknell Forest for Sandhurst and Bracknell, Surrey Heath for Camberley, and the Royal Borough of Windsor and Maidenhead for Ascot. Keep both certificates with the house paperwork. A buyer’s solicitor will usually ask for them when you sell.

• A steel consumer unit with a main switch, surge protection and 30 mA RCD protection.
• A circuit chart in the door, so anyone can find the right breaker.
• A notice on the board saying how to test the RCDs, and how often.
• The Electrical Installation Certificate, with every circuit’s test results.
• The Building Regulations compliance certificate.