“Fuse box” and “consumer unit” usually describe the same thing: the box where your home’s electrical supply is split into separate circuits, each with its own protection. The real difference is age and the type of protection inside. An older fuse box protects circuits with fuses, often rewireable ones, while a modern consumer unit uses circuit breakers that switch off automatically, together with RCDs or RCBOs that also cut the power when they detect current leaking to earth, the kind of fault that can cause an electric shock.
So when people compare a consumer unit with a fuse box, the useful question is not what it’s called. It’s what protection it gives your circuits, and whether that protection still suits the way the property is used.
Thinking about replacing an old board? See our consumer unit and fuse box services in East and South-East London, or read on to understand what you actually have.
What you might find in the cupboard
Most homes have one of four broad types. You can usually tell which one you have by looking at it with the cover closed. There’s no need to open anything or take off a panel.
| What you see | What it usually is | How it protects circuits |
|---|---|---|
| Ceramic or plastic carriers that pull out, sometimes with fuse wire visible | Older fuse box with rewireable (semi-enclosed) fuses | A thin wire melts when too much current flows and has to be replaced by hand |
| Pull-out carriers holding sealed cartridge fuses | Cartridge fuse board | A cartridge fuse fails and is swapped for a new one of the same rating |
| A row of small switches and a main switch, with one RCD or none | Earlier consumer unit with miniature circuit breakers (MCBs) | Breakers trip on overload or short circuit and can be reset. Shock protection may be limited or missing |
| Breakers with a “T” or test button on each one, or two RCDs splitting the circuits into groups, usually in a metal case | Modern consumer unit with RCBOs or a dual-RCD layout | Overload, short-circuit and earth-leakage protection, either per circuit or per group |
Many older properties have a mix, such as a newer unit beside an old fuse board that still feeds a cooker or a shower, or a unit that has been extended over the years. That is one reason the label on the cupboard door tells you very little.
Why the type of protection matters
Fuses and circuit breakers respond to the same faults in different ways
Fuses and miniature circuit breakers both protect cables from overload and short circuits. The practical difference is what happens afterwards. A blown rewireable fuse has to be rewired by hand, and the protection then depends on the right gauge of wire being used. Fit a thicker wire and the circuit may stay on when it should have cut out. A circuit breaker can simply be reset once the cause has been dealt with, and its rating can’t be changed by accident.
RCD protection is the bigger gap in older boards
An RCD (residual current device) watches for current escaping where it shouldn’t, for example through a damaged cable or a person, and cuts the supply within a fraction of a second. Older fuse boxes typically have no RCD at all. Some early consumer units have a single RCD covering only some circuits. Modern units usually protect every circuit, either with one RCBO per circuit or with two RCDs sharing the circuits between them. With RCBOs, a fault on one circuit only switches off that circuit. With a dual-RCD layout, it switches off half the house.
This is the protection most people mean when they talk about “upgrading the fuse box”. It’s also why a newer unit can trip in situations where an old fuse box never seemed to complain.
Things that are often misunderstood
“An old fuse box has to be replaced”
Not automatically. Electrical Safety First’s best-practice guidance for electricians states that a consumer unit need not be replaced simply because it has rewireable fuses, cartridge fuses or older-type circuit breakers, and that a lack of RCD protection can sometimes be added in other ways (Electrical Safety First, Best Practice Guide 1). What matters is the condition of the board and the installation behind it, which can only be judged by inspection and testing.
Age still counts for something, though. Rewireable fuses invite the wrong wire being fitted. Old boards are often worn or damaged, or have been altered piecemeal, and they rarely offer the shock protection modern installations are designed around. Those are good reasons to have an old board assessed, rather than automatic reasons to replace it.
“Plastic consumer units are illegal”
They aren’t. Since Amendment 3 to BS 7671, the UK wiring regulations, new consumer units fitted in homes have needed a non-combustible enclosure, which in practice usually means a metal case. That requirement applies to new installations. The same Electrical Safety First guidance confirms that an existing unit does not need replacing just because its enclosure is plastic.
“A new consumer unit will stop the tripping”
Sometimes it does the opposite, at least at first. Modern RCD protection is more sensitive than an old fuse board, so it can expose faults that were already there, such as damp in an outdoor socket, deteriorated cable insulation or wiring mistakes left by earlier DIY work. If you already have a unit that trips, the cause needs finding before anything is replaced. Our guide on why a circuit breaker keeps tripping explains what different tripping patterns can point to.
If you’re thinking about replacing a fuse box
Replacing a fuse box with a consumer unit is a bigger job than swapping one box for another, because the new unit can only be connected to an installation that’s fit to receive it. A few points are worth knowing before you get quotes:
- The existing installation is checked first. Electrical Safety First’s guidance expects a survey of the installation before replacement, looking at earthing, main protective bonding and the condition of the circuits being reconnected. If those aren’t adequate, remedial work may be needed before or alongside the new unit.
- It is notifiable work. Replacing a consumer unit in a home in England or Wales is notifiable under the Building Regulations. In practice it’s either carried out by an electrician registered with a competent person scheme, who self-certifies it, or it’s notified to building control.
- You should receive a certificate. On completion, an Electrical Installation Certificate with test results for each circuit should be issued. Keep it with your property documents, because buyers and future electricians will want to see it.
- The power will be off for part of the work. The consumer unit feeds the whole property, so the supply is isolated while the board is changed and the circuits are tested.
What the job involves, and what it costs, depends on the number of circuits, the state of the existing wiring and how accessible the board is. Voltify Contractors’ consumer unit and fuse box services page explains how that assessment works and what usually affects the price. If you’d rather start with a general look at the condition of the whole installation, electrical testing and inspection is often the more sensible first step, and our guide to what an electrical safety check covers explains what that involves.
When an old board shouldn’t wait
Some signs call for an electrician soon, whatever type of board you have:
- scorch marks, a burning smell, crackling or buzzing from the board;
- a case that feels hot, or is cracked or melted;
- a fuse that blows or a breaker that trips again straight after being reset;
- visible fuse wire that looks too thick for its carrier, or wire of different thicknesses;
- missing covers that leave live parts exposed.
If any of these are present, don’t keep resetting it or swapping fuses. Leave the cover closed, switch off at the main switch if you can do so safely, and get the board checked. Where there are signs of overheating or burning, our emergency electrician page sets out what happens next.
Key takeaway: “Fuse box” and “consumer unit” mostly differ in age and protection, not in purpose. An old board isn’t automatically unsafe, and a plastic one isn’t automatically non-compliant. What decides whether replacement makes sense is the board’s condition, the level of RCD protection and the state of the installation behind it, all of which need inspecting and testing.
Consumer unit questions we are often asked
What is a consumer unit?
A consumer unit is the modern name for the fuse box. It splits your home’s electrical supply into separate circuits and protects each one with circuit breakers and RCD or RCBO protection, which cuts the power if a fault or leakage to earth is detected.
Do I need to replace my fuse box?
Not automatically. An older board is not necessarily unsafe, but it should be inspected and tested. Replacement makes sense when the board is damaged or overheating, has no adequate RCD protection that can be sensibly added, or the installation behind it needs work.
Is replacing a consumer unit notifiable work?
Yes. In England and Wales it is notifiable under the Building Regulations, so it is either carried out by an electrician registered with a competent person scheme or notified to building control. You should receive an Electrical Installation Certificate afterwards.
Will a new consumer unit stop my circuits tripping?
Not necessarily. Modern RCD protection is more sensitive, so it can reveal faults that were already there. The cause of any tripping should be found before anything is replaced.
Voltify Contractors carries out consumer unit and fuse box work for homes and landlords across East and South-East London, including Canary Wharf, Stratford, Greenwich, Woolwich and Barking. To discuss your board, contact us with a photo of it.
