My fuse box has old rewireable fuses — do I need a new consumer unit?
What an old rewireable board does and does not protect you from, whether replacement is legally required, what a new consumer unit involves, and roughly what it costs.
- Difficulty
- beginner
- Time
- 15 min
- Read
- 5 min
- Safety
- warning
Short answer
You are not legally forced to replace a working rewireable board, but it gives you no protection against electric shock, and it will not satisfy a landlord's EICR, a mortgage survey or most insurers' expectations. If you have no RCD, replacement is the right decision, and it must be done by a qualified electrician because consumer unit work is notifiable.
A board with ceramic carriers and fuse wire protects the cable and nothing else. It cannot detect current leaking to earth, which is the fault that electrocutes people, and it responds slowly to overloads. That is not a small difference in specification — it is a whole category of protection that did not exist when the board was fitted.
Safety
Step by step
- Confirm what you actually have.Rewireable fuses are ceramic or bakelite carriers you pull out, with a thin wire across two screws. Cartridge fuses look similar but hold a sealed cartridge. Neither has a switch, neither has a test button, and neither offers any earth leakage protection.
- Check whether there is any RCD anywhere.Sometimes an old board has had a single RCD added upstream, or there is a separate RCD unit for the shower or the garage. Look for a test button anywhere on or near the board. No test button means no RCD.
- Look at the cable, not just the board.If the cable at the board is black rubber, or cloth-covered, or has a lead sheath, the wiring is likely to be from the 1960s or earlier and the insulation will be perished. That changes the answer from "replace the board" to "get the whole installation assessed", because a new board on failing cables will trip constantly and rightly so.
- Understand what you gain.30mA RCD protection on socket and lighting circuits, individual circuit protection with RCBOs, a main switch you can actually operate, correct labelling, and usually surge protection. In practical terms: a fault becomes an inconvenience rather than a hazard.
- Accept that this is not owner work.Replacing a consumer unit is notifiable work under Part P in England and Wales, with equivalent requirements in Scotland and Northern Ireland. It must be done by a qualified electrician, who will either self-certify through a competent person scheme or notify building control. You should receive an Electrical Installation Certificate.
- Expect the electrician to test before they quote firmly.A good electrician will not fit a new board onto an untested installation. They will test each circuit's insulation resistance and earthing first, because a new RCD will find every existing fault that the old fuses were happily ignoring.
- Budget realistically.A straightforward consumer unit replacement in a typical UK house is broadly in the several-hundred-pound range, commonly around £500 to £900 including testing and certification, more if earthing and bonding need upgrading or if circuits are found to need remedial work. Regional variation is wide. Get two or three quotes.
- Ask specifically what is included.Main earthing conductor and main protective bonding to gas and water upgraded if undersized, any remedial work on circuits found faulty, an Electrical Installation Certificate, and building control notification. Those are the items that turn a cheap quote into an expensive one later.
Tips
- Ask for the test results, not just the certificate. The schedule of test results is the document that tells you the condition of every circuit.
- If the electrician says a circuit needs work before the new board goes on, that is a good sign, not an upsell — the old fuses were simply incapable of noticing the problem.
- Getting the board done at the same time as any other disruptive work saves on making good and on a second visit.
Common mistakes
- Replacing fuse wire with a heavier gauge because it keeps blowing — The fuse wire rating is matched to the cable. Heavier wire lets a cable in a wall run beyond its safe current with nothing to stop it, which is a fire risk with no warning.
- Fitting a new consumer unit onto old cables without testing — Modern RCDs will detect the leakage that perished rubber insulation produces, so the new board trips repeatedly and the owner blames the board. Testing first is what prevents this.
- Choosing the cheapest quote without checking what is excluded — Bonding upgrades and circuit remedials are the usual exclusions and they are the items most likely to be needed in a house old enough to still have fuse wire.
If it doesn't work
Fuse blows repeatedly on one circuit
Cause: A real fault or overload the fuse is correctly reporting — Fix: Unplug everything on that circuit and refit correct-gauge wire once. If it blows again, leave it out and call an electrician.
Board is warm to the touch or smells
Cause: Loose or degraded connections, or overloaded fuseways — Fix: Switch off at the main switch if you safely can and call an electrician the same day. Do not open it.
A carrier is discoloured or the porcelain is cracked
Cause: Sustained heat at that fuseway — Fix: This is end of life for the board. Stop using that circuit and arrange replacement.
Questions people ask
Is it illegal to still have a rewireable fuse box?
No. Existing installations are not required to be brought up to the current edition of the wiring regulations simply because the regulations changed. But if you are a landlord, the mandatory EICR will very likely record the lack of RCD protection as a C2 (potentially dangerous) code, which must be remedied.
Will my insurer refuse a claim?
Insurers rarely exclude old boards outright, but they do ask about the condition of the installation, and a fire traced to an installation known to be unsafe is a much harder claim. An EICR with satisfactory results is the document that settles the question.
Can I just add an RCD to the existing board?
Sometimes an electrician can fit an RCD enclosure upstream as an interim measure, but it is often nearly as much work as a proper replacement and leaves the old fuseways in place. Ask, but expect the recommendation to be a new board.
What about the wiring itself?
If the board is being replaced and testing shows healthy insulation resistance on modern PVC twin-and-earth, the wiring is usually fine and a board change is all you need. Rubber, lead-sheathed or cloth-covered cable is a different conversation, and that one ends in a rewire.