When Should I Replace My Fuse Box or Consumer Unit?

Your consumer unit — still often called the fuse box — controls and protects every circuit in your home. When it's old, damaged or missing modern protection, every socket, light and appliance in the house is running on a weaker safety net. This guide covers the practical signs it's time to replace, what current UK regulations require, and what the process actually looks like.

What a modern consumer unit actually does

A modern 18th Edition consumer unit protects against three separate risks. Miniature circuit breakers (MCBs) cut power on overload. Residual current devices (RCDs) protect against electric shock by disconnecting when they detect current leaking to earth. And Surge Protection Devices (SPDs) — required on many new installations — protect sensitive electronics against voltage spikes. Older units often have only rewireable fuses and no earth-leakage protection at all.

Sign 1: Rewireable ceramic fuses

If your unit uses ceramic fuse carriers with visible fuse wire, it dates from the 1970s or earlier. It has no RCD protection whatsoever, which is a C2 (potentially dangerous) code on any EICR and effectively unlettable if you're a landlord. Replacement is not optional here — it's the biggest single safety upgrade you can make to a home.

Sign 2: A plastic enclosure

The 18th Edition (BS 7671:2018) requires that consumer units and similar switchgear inside domestic premises are made of non-combustible material — typically steel — or enclosed within a non-combustible cabinet. Plastic units aren't automatically dangerous, but they're no longer compliant for new installations. Combined with age, RCD limitations or damage, replacement is strongly advised.

Sign 3: A single RCD serving everything

Early split-load consumer units used one RCD covering half of the circuits. If that RCD trips — say, from a failing kettle — you lose everything on that side, including fridge, freezer and lights. Modern RCBO consumer units combine RCD and MCB in a single device per circuit, so a fault on one circuit doesn't take out the whole house.

Sign 4: Nuisance tripping

Repeated trips are your consumer unit telling you something. Sometimes it's a genuine fault — insulation breakdown in old cabling, a leaky immersion element, a faulty appliance. Sometimes it's cumulative earth leakage from many appliances sharing one RCD. Either way, the fix is often a per-circuit RCBO upgrade plus a proper investigation.

Sign 5: Physical warning signs

Warm cover panels, brown or black scorching around a fuse holder, humming sounds, corrosion, or a burning plastic smell all mean overheating inside the enclosure. Isolate the affected circuit at the main switch and call an electrician immediately. Do not try to open the cover yourself.

What the replacement process looks like

A straightforward like-for-like consumer unit swap in a well-maintained home usually takes 4–6 hours. We isolate the incoming supply (co-ordinating with your DNO/supplier if needed), remove the old unit, install a metal-clad unit with per-circuit RCBOs, test every circuit for insulation resistance, continuity, earth fault loop impedance and RCD trip times, then issue an Electrical Installation Certificate (EIC) and register the work with Building Control where notifiable.

When a rewire is the honest answer

Sometimes we open a consumer unit and find deteriorated rubber-insulated cabling, unsafe joints or missing earth conductors. Fitting a new unit onto that installation would be papering over a genuine hazard. In these cases we're upfront: the wiring itself needs replacing, and we'll quote for a partial or full rewire rather than a cosmetic upgrade.

Ready to check yours?

If you're not sure whether your unit is safe or compliant, book a free inspection. We'll open the cover, walk you through what's there, and give you a written recommendation — with clear pricing and no pressure to proceed.