Consumer Unit Installation & Replacement

What does a consumer unit do?

The consumer unit (often still called a fuse box) takes the electricity supplied to your property and divides it into individual circuits — lighting, sockets, cooker, shower and so on. Each circuit is protected by a device that disconnects the supply if something goes wrong, such as an overload, a short circuit or current leaking to earth.

New consumer unit installation

A new consumer unit is typically installed as part of a rewire, a new build, a large extension or a conversion where the existing board can't sensibly accommodate the new circuits. The board is sized for the number of circuits needed, with space for future additions such as an EV charger or garden supply.

Consumer unit replacement

Replacement means removing an existing board and fitting a modern one in its place. It is common in properties with older fuse boxes, boards that have been damaged, or installations where the existing unit no longer offers suitable protection. If you're unsure whether yours needs replacing, our guide on when to replace a consumer unit covers the common warning signs.

Upgrading an existing installation

Sometimes the board itself is only part of the picture. Before a new unit can be fitted, the electrician needs to be satisfied that the earthing and protective bonding are adequate and that the circuits are in a safe condition. If faults are found on existing circuits, these may need attention before the new board can be energised — modern protective devices will often reveal faults an old fuse box was hiding.

RCD and RCBO protection

A residual current device (RCD) detects current leaking to earth — for example through a person touching a live part — and disconnects the supply very quickly. An RCBO combines RCD protection with overcurrent protection in a single device for each circuit.

With a board where several circuits share one RCD, a single fault can switch off all of them. With RCBOs, only the affected circuit trips, so the rest of the house stays on. RCBO boards usually cost more, which is one reason quotes can vary.

Circuit identification

Every circuit should be clearly labelled at the board so you know which breaker controls which part of the property. Good labelling makes resetting a tripped circuit straightforward and helps any electrician working on the installation in future.

Testing and certification

Once installed, the circuits connected to the new board are tested — including insulation resistance, continuity of protective conductors, earth fault loop impedance and RCD operation. Replacing a consumer unit is notifiable work under Part P of the Building Regulations in England, so you should receive an Electrical Installation Certificate and a Building Regulations compliance certificate from a registered electrician. EMI Electrical is NAPIT registered.

What to expect on the day

• The power to the property will be off for most of the working day.
• The old board is removed and the new one fitted and connected.
• Circuits are tested, labelled and re-energised.
• You'll be shown how the new board works and how to reset a trip.
• Certificates follow once the paperwork is completed.

It's worth planning around the power-off period — freezer contents, home working and any medical equipment should be considered in advance.

Common reasons for upgrading

• An old rewirable fuse box with no RCD protection
• Adding circuits for an extension, kitchen, EV charger or heat pump
• Nuisance tripping that takes out several circuits at once
• Damage, overheating or recommendations made on an EICR

Why use a qualified electrician?

Consumer unit work involves the supply to the whole property. It must be carried out by a competent person, tested properly and certified. DIY replacement is dangerous and will leave you without the certification you'll need when you sell or let the property.

Related guides

• What affects consumer unit replacement cost
• Consumer unit replacement in Hertfordshire
• When should you replace a consumer unit?