A consumer unit upgrade replaces an old fuse board with one providing RCD or RCBO protection to each circuit — the single biggest safety improvement available on most older installations. It is notifiable work. Crucially, the existing circuits must be tested first: fitting a sensitive new board onto deteriorating cable reveals faults that were previously invisible.
- Test before you buy. A new board on perished cable will trip constantly, and the board is not at fault.
- RCBOs mean one faulty circuit does not take out half the house. Worth the difference.
- Consumer unit replacement is notifiable and must be certificated.
- A modern board on old wiring is not a rewire, and should not be sold as one.
What the board actually does
The consumer unit is where the incoming supply is divided into the circuits that serve the house, and where the protective devices sit. It has two jobs: protect the cables from carrying more current than they can handle, and — on a modern board — disconnect quickly if current starts leaking to earth.
An older board does only the first of those. A rewireable fuse board, or an early board with only MCBs, protects the cable but offers nothing against a person touching a live part or a cable being damaged. That is the gap a modern board closes, and it is why upgrading is the most effective single improvement available on most older installations.
The devices, without the jargon
| Device | What it does | Worth having? |
|---|---|---|
| Fuse (rewireable) | Melts on overload. No earth leakage protection | Obsolete — the reason to upgrade |
| MCB | Trips on overload and short circuit | Standard, but not sufficient alone |
| RCD | Disconnects on earth leakage, covering several circuits | Essential; shared RCD is the compromise |
| RCBO | MCB and RCD combined, one per circuit | Yes — a fault affects only that circuit |
| SPD | Surge protection against voltage spikes | Often included; useful with lots of electronics |
| AFDD | Detects arc faults in damaged cable | Required in some situations; discuss |
| Main switch | Isolates everything | Always present |
The practical difference between a shared RCD and RCBOs is what happens when something trips. With a shared RCD, one faulty appliance takes out several circuits at once — which matters for freezers, boilers and anyone working from home.
Why the circuits must be tested first
This is the part most often skipped, and it is the cause of nearly every unhappy consumer unit job.
An old fuse board is not sensitive to earth leakage. Cable insulation can have been slowly deteriorating for decades and the board will never have noticed, because it was not looking.
Fit a modern board with RCD protection and it is looking. All that pre-existing leakage, which was always there and never detected, now registers — and the new board trips. Repeatedly.
At that point the customer reasonably concludes the new board is faulty, or that the electrician has done something wrong. Neither is true: the board is correctly reporting the condition of the wiring behind it.
This is why a proper consumer unit quote includes testing the existing circuits first. If the insulation resistance results are poor, you need to know that before the board is ordered, because the honest answer may be that the installation needs rewiring rather than a new board on top of it.
What the job involves
- Test the existing installation — insulation resistance, continuity, earthing and bonding. This decides whether the job should proceed as planned.
- Check the main earthing arrangement and main bonding to gas and water, upgrading if undersized. Very common on older properties.
- Arrange the supply isolation. Pulling the main fuse is the supplier's responsibility, and depending on the arrangement may need to be booked.
- Remove the old board and fit the new enclosure, which must be non-combustible or in a non-combustible enclosure.
- Reconnect each circuit to its own protective device, correctly rated.
- Test every circuit again and record the results.
- Label the board accurately — which way feeds what.
- Issue the Electrical Installation Certificate and notify Building Control.
- Walk you through the board and show you how to reset and test it.
Most of a day for a straightforward replacement, longer if remedial work is found. The power is off for a substantial part of it.
When a new board is the wrong purchase
There are situations where we would advise against it, or against doing it in isolation.
- The cable is at the end of its life. Rubber, lead or fabric-sheathed cable, or poor insulation resistance across the board. A new consumer unit on that is money spent on the visible part of a problem that lives elsewhere.
- A rewire is planned anyway within a year or two. The board is part of a rewire; doing it separately first means paying twice for the same isolation and testing.
- Major works are coming. An extension or loft conversion will add circuits. Sizing the board for what the house is about to become is cheaper than replacing it again.
- There is no earthing or bonding to speak of. Those need resolving as part of the job, not after it — and they change the price.
- The existing board is genuinely modern and compliant. Occasionally someone has been told they need an upgrade when they have a perfectly good board. Ask what specifically is deficient.
Notification, certification and insurance
Replacing a consumer unit is notifiable work under Part P in England. It must be either self-certified by someone registered with a competent person scheme and notified on your behalf, or notified to Building Control in advance and inspected.
You should receive an Electrical Installation Certificate recording the test results for every circuit, and in due course confirmation of the notification. Keep both with the deeds — the certificate is what a buyer's solicitor asks for, and a consumer unit with no paperwork is a predictable conveyancing enquiry.
It matters for insurance too. An uncertificated board replacement is an awkward thing to be explaining after a fire.
What it costs
These are the electrical figures published across this site:
| Job | Typical Coventry guide price | Notes |
|---|---|---|
| Consumer unit upgrade | £450–£700 | RCD protection |
| EICR (3-bed) | £150–£300 | Safety certificate |
| Full rewire (3-bed) | £3,000–£6,000 | Whole-house |
| Electrician, hourly | £45–£90/hr | Certified, Part P |
| Typical job | £233–£473 | Sockets, lighting, faults |
Where testing reveals remedial work — upgrading main bonding, correcting a circuit, dealing with poor insulation resistance — that is additional and should be quoted once the test results are known rather than assumed away.
We test the existing circuits before quoting, because that decides whether a new board is the right purchase at all.
Frequently asked questions
How long does a consumer unit upgrade take?
Most of a day for a straightforward replacement, with the power off for a substantial part of it. It takes longer where testing reveals remedial work, where main bonding needs upgrading, or where circuits are unlabelled and have to be identified first. Plan for a day without power rather than a couple of hours.
Why does my new consumer unit keep tripping?
Almost always because it is detecting earth leakage that the old board was never able to see. Deteriorating cable insulation, a failing appliance or accumulated leakage across many circuits were all present before; the new board is simply the first thing capable of noticing. It needs testing to locate, and it is why circuits should be tested before the board is fitted.
Do I need RCBOs or is a shared RCD enough?
A shared RCD meets the requirement; RCBOs are better in use. With a shared RCD one faulty appliance takes out every circuit on it, which is a real nuisance if it includes the freezer, the boiler or your home office. RCBOs confine the trip to the circuit at fault. The cost difference is usually modest relative to the job.
Is replacing a fuse board notifiable?
Yes. Consumer unit replacement is notifiable work under Part P in England, whether or not it is like-for-like. It must be self-certified by a scheme-registered installer who notifies on your behalf, or notified to Building Control in advance. You should receive an Electrical Installation Certificate either way.
Will a new consumer unit fix my old wiring?
No, and it should not be sold as though it will. It improves protection at the board, which is genuinely valuable, but the cables, sockets and switches are unchanged. If the wiring itself is at the end of its life, a new board is the visible part of a problem that lives behind the plaster.
What is an SPD and do I need one?
A surge protection device limits damage from voltage spikes, which typically come from lightning activity or switching events on the network. It is commonly included in modern boards. Whether it is worthwhile depends on the value of the electronics in the house and the supply arrangement — worth a conversation rather than an automatic yes or no.
Tested first, then quoted
We test the existing circuits before recommending a board, so you are not buying a new unit that will trip on old cable. Free quote, certificated work, notification handled.