Almost everyone who calls about a consumer unit has been told they need one. Very few have been told why. The word "regulations" gets used to close the conversation rather than to open it, which is a shame, because the reasoning behind a modern board is not complicated and it is worth understanding — not least because it tells you when an upgrade is genuinely necessary and when it is somebody's preference.
This page explains what a consumer unit is required to do, how the requirements have moved, and what that means for an ordinary Central London flat with a board that has been sitting in a hallway cupboard since long before anyone thought about it.
The board's actual job
A consumer unit takes the supply from your meter and divides it into circuits, giving each one protection. It is protecting three different things, and they are worth separating because each one has driven a change in the equipment.
- The cable. If a circuit draws more current than its cable can carry, the cable heats. Overcurrent protection — the fuse, or the modern circuit breaker — is there to disconnect before the cable becomes a fire.
- You. If current finds a path to earth through a person, no amount of overcurrent protection will help; the current involved is far too small to blow a fuse and more than enough to kill. That is what an RCD is for. It watches for current going out that does not come back and disconnects in a fraction of a second.
- The building. Loose or deteriorating connections can produce arcing that never draws enough current to trip anything, and arcing sets fire to things. This is the concern behind the newest generation of devices.
Every significant change to consumer unit requirements over the last few decades maps onto one of those three. Once you see that, the equipment stops being alphabet soup.
How the equipment has moved
Rewireable fuses
Still found in Central London, particularly in flats that have not been touched since a long tenancy. A wire that melts. It protects cable and nothing else, it offers no protection against shock, and its worst feature is that it can be repaired with the wrong wire by a well-meaning householder — at which point the protection is gone and nothing tells you.
Circuit breakers
The same job, done more precisely and resettably. An improvement, but still only overcurrent protection. A board full of MCBs and no RCD is a common intermediate generation and, in most modern assessments, an incomplete one.
Split-load boards with RCDs
The arrangement most people have: circuits divided across two RCDs so that a fault on one side does not black out the whole flat. Much safer. Its weakness is nuisance tripping — an RCD covering six circuits will take all six off when any one of them misbehaves, and the accumulated small leakage of many appliances can trip it with nothing actually broken. This is the single most common cause of the mysterious tripping described in our guide to no power and a tripping fuse box.
Individual protection per circuit
The current preference in most new work: each circuit gets its own combined device, so a fault takes out one circuit and leaves the rest alone. It costs more and it is worth it, particularly in a flat where the freezer, the router and the alarm are on circuits you would rather not lose because a bathroom extractor failed at 2am.
Surge and arc-fault devices
Modern boards may also include surge protection and, in some cases, arc fault detection. Whether these are required in your particular installation is a design assessment made against the current edition of BS 7671 by the person designing the work — not a universal yes or no, and not something we would state as a blanket rule on a web page. Ask your electrician to explain what they are proposing and why it applies to your installation.
What the rules actually require
Two things are worth stating plainly. Electrical work in dwellings falls under Building Regulations Part P. Installations are designed, installed and tested to BS 7671, the wiring regulations. Replacing a consumer unit is notifiable work: it needs to be carried out by someone competent, certified, and notified through the appropriate route. You should finish the job holding a certificate. If you do not, you have paid for the work but not for the evidence that it was done properly — and that evidence is what a buyer's solicitor or a managing agent will ask for later.
A more common current requirement worth knowing about is the enclosure itself. Modern practice under the current standard is for domestic consumer units to be housed in a non-combustible enclosure, which is why boards fitted today are almost always metal where older ones were plastic. That change came from a straightforward observation: a loose connection inside a plastic box can set the box alight.
"Is my old board illegal?"
No — and this is where a lot of pressure selling happens. The wiring regulations are not generally retrospective. An installation that was compliant when it was done does not become unlawful because the standard has moved on. What an older board is, is less safe than a current one, and that difference is assessed through inspection rather than through age. An inspection may record observations against it; those observations are coded according to how serious they are, and a code is not automatically an instruction to replace the board.
So the correct question is not "does my board meet the current regulations" — very few older boards do — but "what did the testing find, and what is the proportionate response?" Our guide to EICR certificates explains how that inspection works and what the codes mean.
When an upgrade genuinely is the answer
There are situations where a board change stops being optional in practice:
- An inspection has recorded observations that cannot be addressed at the board without replacing it.
- There is no RCD protection where the current standard would require it, and there is no way to add it to the existing board.
- The board is obsolete to the point where protective devices for it cannot be obtained, so any future circuit change is blocked.
- You are adding significant load or new circuits — a kitchen, an electric shower, or an EV charger — and the existing board has neither the ways nor the protection to take them.
- The enclosure or its internals show heat damage, which is not a "monitor it" situation.
- Nuisance tripping is being caused by the board's arrangement rather than by a fault, and redistributing the load is the engineering answer.
Landlords have an additional driver. Rented homes in England require an EICR at least every five years under the Electrical Safety Standards in the Private Rented Sector (England) Regulations 2020, and remedial work identified in that report has to be dealt with. Our guide to EICR landlord requirements covers those duties.
The upgrade surfaces things — and that is the point
The most important thing to understand before commissioning a board change is that a new board tests the installation behind it. Old rewireable fuses tolerated conditions that a modern RCD will not: damp in an outside circuit, degraded insulation on an old lighting run, a neutral borrowed between circuits, an appliance quietly leaking to earth for a decade. Fit a sensitive board and those conditions stop being invisible.
Clients sometimes read this as the electrician creating work. It is the opposite: those conditions existed yesterday, and the old board's contribution was to say nothing about them. In older Central London stock — Victorian conversions in W2, mansion block flats in NW8 and W9, ex-commercial buildings in Fitzrovia — this is common enough that it should be anticipated in the plan rather than treated as a shock. A good electrician tests before quoting for exactly this reason, and our page on what drives fuse board replacement cost explains why a number given before testing is not worth much.
The block dimension
In a flat, part of the installation is not yours. The intake, the main fuse and often the meter sit in communal cupboards or a basement plant room, controlled by the porter or the managing agent, and access has to be arranged. If safe isolation needs the main fuse pulled, the distributor may need to be involved on their own timescale. Most leases also require consent for alterations, and while a like-for-like board replacement within your demise is usually less contentious than relocating it, you should confirm the position with your managing agent rather than assume. Where a block undertakes electrical works communally, Section 20 consultation under the Landlord and Tenant Act 1985 applies to works over £250 per leaseholder.
What to ask before you agree
Ask what the testing found, and to see it. Ask what protective devices are proposed and why. Ask whether surge or arc-fault protection is being included and what the reasoning is. Ask what happens if a circuit fails its tests once the new board is on — who decides, and at what price. Ask how long the supply will be off. Ask what certification you receive. A quote that cannot answer those is a number, not a proposal.
How we do it
We test first, explain what the results mean in plain terms, and give a fixed price against a written scope before anything is isolated. If your board is old but the installation behind it is sound, we will tell you that too. Electrical work starts from £80 and the set prices are published on the electrical page. Across the W2 stock this is handled by the same team behind our Paddington electrician page, and for landlords and managed portfolios, board and inspection work is far cheaper planned in than met as an emergency.
If you have been told you need a new board and want a second opinion based on measurements rather than assertion, send us the details and a photo of the board with its cover on.