The consumer unit — commonly called the fuse board or fuse box — is the hub of your home’s electrical system. It receives the incoming supply from the meter, divides it into individual circuits, and protects those circuits with fuses or circuit breakers. An outdated or undersized consumer unit is both a practical inconvenience and a safety concern: it may not provide adequate protection against electric shock or fire, and it will fail a periodic electrical inspection.
For most UK homes, a consumer unit replacement costs £400–£900 supply and fit, completed in half a day by a qualified electrician. The work must be notified under Part P of the Building Regulations.
Types of Consumer Unit
Old rewireable fuse boards
Pre-1960s properties often have rewireable fuse boards where each circuit is protected by a porcelain fuseholder with a thin fuse wire that the homeowner replaces when it blows. These boards provide no RCD (residual current device) protection and do not trip instantly — they rely on the fuse wire melting, which takes time. They should be replaced.
MCB-only consumer units (pre-2016)
From the 1980s onward, miniature circuit breakers (MCBs) replaced rewireable fuses. MCBs trip quickly and are reset by a switch rather than requiring fuse wire replacement. However, older MCB-only boards provide no RCD protection. Under the 17th Edition of the Wiring Regulations (BS 7671:2008), new installations required at least two RCDs covering all circuits, but many existing boards from the 1990s–2000s were installed before this was fully enforced.
Split-load dual RCD consumer units
The most common type installed from around 2008 to 2016. The board has a main switch and two RCDs (40 A, 30 mA), each protecting half the circuits. This provides RCD protection throughout, but has one significant weakness: if one RCD trips, it takes out all the circuits it covers simultaneously — losing, for example, both the freezer and the shower at once. Still acceptable in existing installations, but less convenient and less safe than RCBO boards.
RCBO consumer units
An RCBO (residual current breaker with overcurrent) combines MCB and RCD functions in a single device per circuit. Every circuit has its own independent protection: a fault on the shower circuit trips only the shower breaker, leaving all other circuits unaffected. This is now the preferred standard for new consumer unit installations. Supply cost for the unit is higher (RCBOs cost £15–£35 each versus £5–£10 per MCB), but the board requires only a single main switch.
Consumer unit types at a glance
| Type | RCD protection | Individual trip per fault | Notes |
|---|---|---|---|
| Rewireable fuse board | None | No — fuse wire needed | Replace immediately |
| MCB-only board | None | Yes | No RCD = non-compliant for new work |
| Split-load dual RCD | Yes (2 groups) | No — half the circuits trip | Acceptable in existing dwellings; not ideal |
| RCBO board | Yes (per circuit) | Yes | Current best practice; required in new |
| High-integrity (dual RCD + RCBOs) | Yes | Partial | Legacy design; largely superseded by RCBO |
Regulatory Requirements: BS 7671 and Part P
The 18th Edition of the Wiring Regulations (BS 7671:2018, with Amendment 2 effective April 2022) requires:
- Metal-clad enclosures for all new consumer units in domestic premises (since Amendment 3 in 2016). Plastic-encased units are no longer acceptable for new installations or full replacements in homes — the metal enclosure provides fire containment if an internal fault ignites.
- RCD protection on all circuits in new consumer unit installations.
- Surge protection devices (SPDs) — Amendment 2 (2022) introduced a new requirement to assess the need for SPDs in new installations and significant changes to existing ones. For most domestic properties at risk of lightning-induced surges, a Type 2 SPD at the consumer unit is now expected.
All consumer unit replacements in England and Wales are notifiable under Part P of the Building Regulations. A registered Part P electrician self-certifies the work; work done by an unregistered contractor must be inspected and certified by Building Control (with a fee). A completion certificate must be provided to the homeowner.
When Should You Upgrade?
Replace your consumer unit if:
- It is a rewireable fuse board — immediate safety risk; no rapid disconnection on fault
- It has no RCD protection — non-compliant with current standards; fails an EICR
- It is in a plastic enclosure — no longer acceptable for full replacements
- The board is full — no spare ways for additional circuits (EV charger, shed supply, electric shower)
- It fails an Electrical Installation Condition Report (EICR) — an EICR is now required on all new private rental tenancies (since July 2020) and at least every five years; a C2 (potentially dangerous) or C1 (immediate danger) code on the board triggers required remedial work
- You are extending, adding a new circuit, or installing an EV charger — this triggers a partial assessment; if the existing board cannot accommodate the new circuit safely, replacement is required
Selling a property: consumer units are inspected during a house buyer’s survey. A visibly old or incomplete board will prompt a surveyor’s recommendation for an EICR, potentially affecting the sale price or requiring upgrade before exchange.
Cost Breakdown
| Item | Typical cost |
|---|---|
| Consumer unit (RCBO, metal-clad, 10–16 way) | £120–£350 supply |
| Electrician labour (half-day, replacement only) | £250–£450 |
| EICR (test before or after) | £150–£300 |
| Part P notification fee (via registered electrician — included in most quotes) | £0–£50 |
| SPD addition | £80–£200 supply and fit |
| Full replacement (supply, fit, EICR, Part P notification) | £400–£900 |
Prices vary significantly by region — London and the South East run 20–40% above the national average for electrical labour.
Additional costs arise if:
- The incoming tails (the cables from the meter to the consumer unit) need replacing — £100–£200 extra for new meter tails
- The earthing or bonding is deficient — supplementary bonding in a bathroom costs £80–£150; main bonding to gas and water service is required at the consumer unit
- Multiple circuits are found to be non-compliant during the EICR — remedial work is quoted separately per fault
Choosing a Consumer Unit: What to Specify
When getting quotes, be clear about:
- Number of ways (circuits): count your existing circuits plus any planned additions. A 12-way board is typical for a three-bedroom house; a 16-way gives more capacity for EV charger, electric shower, garden power, etc.
- RCBO vs split-load: always specify RCBO for a new installation — the price difference is modest at the whole-job level
- SPD: ask whether the quote includes an SPD; under current regulations it should be assessed and usually fitted
- Metal enclosure: confirm the unit being installed is metal-clad; plastic boards must not be installed as replacements
Always use a registered electrician from a recognised scheme such as NICEIC, NAPIT, SELECT (Scotland), or ECA. Ask for the Part P completion certificate and keep it with the property documents.
What the Electrician Will Check
A conscientious electrician will not simply swap the consumer unit and leave. Before and after the replacement they should:
- Test insulation resistance on all circuits (identifies damaged cables that cannot be seen visually)
- Verify earthing and bonding at all required points
- Test RCD operation (response time must be within 40 ms at rated tripping current)
- Verify ring main continuity and polarity
- Issue an Electrical Installation Certificate (EIC) for the new work and an EICR for the existing installation
If the electrician proposes to install a new board without testing the circuits first, or without issuing a completion certificate, do not proceed.
