The short answer
Wiring a consumer unit means connecting the incoming supply cables to a main isolating switch, then routing each circuit's live, neutral and earth conductors to the appropriate protective device — an MCB, RCD or RCBO — and from there through the busbar system inside the unit. Under Part P of the Building Regulations in England and Wales, this is notifiable work: it must be carried out by a registered (competent-person) electrician who self-certifies the installation to BS 7671 (the 18th Edition wiring regulations), or else notified to building control before work begins. Doing it without proper certification leaves the installation legally uncertified, creates a genuine safety risk, and can cause problems when selling the property.
The wiring of a consumer unit is a precise, technically demanding task governed by detailed rules in BS 7671. This page explains what is involved and why the regulations require it to be carried out and certified by a qualified, registered person.
Key facts about the work
- Regulatory standardBS 7671 18th Edition wiring regulations
- Part P statusnotifiable in England and Wales
- Who must do itregistered (competent-person) electrician
- Certificate issuedElectrical Installation Certificate (EIC)
- Main hazardlive 230 V supply; risk of fire and electric shock
What wiring a consumer unit involves
A consumer unit is the point where the incoming mains supply is distributed to the individual circuits in a building. Wiring it involves a sequence of technically precise steps, each governed by BS 7671:
- Incoming supply: the service cable from the meter enters the unit and connects to the main isolating switch (the large switch at the top or side of the board). This is the point from which the entire installation is controlled. Crucially, the cable from the electricity meter to the isolator remains live even when the isolator is switched off — only the distribution network operator (DNO) can make that part dead.
- Busbars: inside the unit, live and neutral busbars run along the board and distribute the supply to each device. Every MCB, RCD and RCBO clips or connects onto these bars.
- Protective devices: each circuit has its own protective device — an MCB (overload protection only), an RCD-protected MCB arrangement, or an RCBO (overload and residual-current protection in one). The correct rating for each device depends on the cable size, the load and the circuit type.
- Circuit conductors: each circuit's live (brown), neutral (blue) and earth (green-and-yellow) conductors connect to the relevant device, the neutral bar and the earth terminal bar respectively. Correct termination — right cable, right terminal, right torque — is essential.
- SPD: since Amendment 2 of BS 7671 (incorporated in the 18th Edition), surge protection devices (SPDs) are required in new consumer unit installations in many situations. If fitted, the SPD connects to the busbar and provides a path for transient overvoltages.
- Testing: once wired, the installation undergoes a series of tests — insulation resistance, earth continuity, polarity, prospective fault current, RCD trip times — before the Electrical Installation Certificate can be issued.
Why this is notifiable work under Part P
Part P of the Building Regulations (England and Wales) defines certain electrical work in dwellings as notifiable because of the risk it poses if done incorrectly. Replacing a consumer unit is specifically listed as notifiable work. This means it must be either:
- carried out by an electrician registered under a government-authorised competent-person scheme — organisations such as NICEIC, NAPIT, ELECSA or STROMA — who self-certifies the work and issues the required certificates; or
- notified to the local authority's building control department before work starts, with an inspection and approval after completion.
The competent-person route is the standard one for a consumer unit replacement. A registered electrician knows the regulations, carries the insurance and indemnity required, and issues the Electrical Installation Certificate (EIC) as a matter of course. A building control route is technically available but less common for this type of work.
What happens if work is done without certification
Uncertified consumer unit work is a real and documented problem. The consequences include:
- Safety: incorrect wiring — wrong device ratings, reversed polarity, poor terminations, inadequate earthing — can cause electric shock or fire. Testing exists precisely to find these faults before the board is put into service.
- Legal status: in England and Wales, notifiable work carried out without certification is in breach of the Building Regulations. The local authority can require it to be inspected and, if non-compliant, rectified at the owner's cost.
- Property sale: solicitors routinely ask for the EIC and Building Regulations compliance certificate when a house is sold. Uncertified work can delay or jeopardise a sale, and buyers' conveyancers will flag it.
- Insurance: a fire or damage event caused by uncertified electrical work may give an insurer grounds to dispute a claim.
The correct position is straightforward: a registered electrician does the work, issues the EIC, makes the Part P notification, and you receive both the EIC and the Building Regulations compliance certificate on completion.
The certificates you should receive
On completion of a consumer unit replacement by a registered electrician you should receive:
- Electrical Installation Certificate (EIC): this records the technical details of the new installation — the devices fitted, their ratings, the test results for each circuit — and confirms compliance with BS 7671. It is issued by the electrician who did the work. Keep it with your property documents.
- Building Regulations compliance certificate: issued (or arranged by the electrician) via the competent-person scheme, confirming that the Part P notification has been made. This is the document that shows building control sign-off was obtained.
If an electrician completes a consumer unit replacement and does not provide both of these documents, ask for them before making final payment. They are a normal part of the job, not optional extras.
| Document | What it records | Issued by |
|---|---|---|
| Electrical Installation Certificate (EIC) | Technical details and test results to BS 7671 | The registered electrician |
| Building Regulations compliance certificate | Part P notification and sign-off | Via competent-person scheme |
Standard documents for a notifiable consumer unit replacement in England and Wales. Sources: Part P of the Building Regulations; BS 7671 18th Edition.
Frequently asked questions
Can I wire a consumer unit myself?
In England and Wales a consumer unit replacement is notifiable work under Part P of the Building Regulations, so it must be done by a registered (competent-person) electrician who self-certifies the work, or otherwise notified to building control. It is not legal to do it yourself without notification and certification, and the safety risks — particularly from the live incoming tails — are serious.
What qualifications does an electrician need to wire a consumer unit?
The electrician must be competent to work to BS 7671 (the 18th Edition wiring regulations) and registered under a government-authorised competent-person scheme such as NICEIC, NAPIT, ELECSA or STROMA. Registration means they have been assessed as having the knowledge, skills and equipment to certify their own work.
What test does a consumer unit need after wiring?
Before an Electrical Installation Certificate can be issued, the circuits must pass a series of tests including insulation resistance, earth continuity, polarity checks, prospective fault current measurement, and — where RCDs or RCBOs are fitted — residual-current disconnection time tests. These verify the installation is safe and meets BS 7671.
Sources & further reading
- Electrical Safety First — replacing a consumer unit (best practice guide)
- IET — BS 7671 18th Edition wiring regulations overview
- NAPIT — Part P competent person scheme
Figures on this page are typical UK ranges drawn from published sources and depend on your specific property and installation. They are guidance, not a quotation.