How to Wire
a Consumer Unit
A homeowner walkthrough of how UK consumer units are wired under BS 7671. Why the job is notifiable Part P work, what a qualified electrician actually does on the day plus what stays the same on every modern install in Milton Keynes.
A UK consumer unit is wired by feeding the meter tails into a main switch, distributing power across RCD or RCBO protection devices, then connecting each circuit (lights, sockets, cooker, shower, EV, immersion) to its own protective device on the busbar. Earthing terminates at the main earthing terminal with main protective bonding to gas plus water services. Under Part P of the Building Regulations, replacing or installing a consumer unit is notifiable work plus it must be carried out by a qualified electrician. This is not a DIY job.
Four figures that shape
every consumer unit install
These are not preferences. They are wiring standards every electrician must follow under BS 7671 plus Part P of the Building Regulations.
BS 7671 Standard
Every UK consumer unit installed today must comply with the 18th Edition Wiring Regulations including amendments.
RCD Trip Threshold
The maximum residual current allowed before an RCD or RCBO must disconnect the circuit to protect against shock.
Typical Main Switch
The standard incoming rating on a domestic UK service plus the main switch sized to match it.
Notifiable Work
A consumer unit replacement is always notifiable. It must be done by a registered electrician then certified.
How a consumer unit
actually gets wired
Every modern install follows the same four stages. The order matters. Skipping any stage breaks compliance plus risks a failed Electrical Installation Certificate at sign-off.
Isolate plus Test
Mains tails are isolated at the meter (DNO permission required). Voltage is proved dead with a calibrated tester before any conductor is touched.
Mount plus Terminate
The new metal enclosure is mounted, meter tails terminated to the main switch then the main earth lands on the main earthing terminal.
Distribute Circuits
Each existing circuit is identified, terminated under the correct RCBO or RCD bank then torque-tightened to manufacturer spec.
Test plus Certify
Insulation resistance, earth fault loop, RCD trip times plus polarity are all tested. An EIC is issued plus the work is notified to Building Control.
Wiring a consumer unit is regulated work, not a how-to project
This guide explains how a consumer unit is wired so you understand exactly what your electrician is doing on the day. It is not a step-by-step to wire your own board. Replacing or installing a consumer unit is notifiable under Part P of the Building Regulations. Doing it without certification is a criminal offence in England plus Wales, invalidates home insurance plus will fail any future EICR or conveyancing check.
That said, knowing the structure of the job helps you spot a sloppy install. A modern consumer unit (sometimes called a fuse board or distribution board) sits between your incoming supply plus every circuit in the property. It carries three jobs: switching, protecting plus distributing. Every wire entering the box has a defined role.
The incoming side
Power arrives from the meter via two thick insulated cables called meter tails. These are typically 25mm² on a 100A service. They terminate first into the main switch at one end of the consumer unit. The main switch is a double-pole isolator, meaning it cuts both line plus neutral when operated, allowing the whole installation to be killed in a single movement.
Sitting next to the main switch is the main earthing terminal (MET). The supply earth from the DNO (or an earth electrode on TT systems) lands here. Every circuit protective conductor (CPC, the green-and-yellow earth wire) eventually traces back to this terminal. Main protective bonding to incoming gas plus water services also originates here, typically in 10mm² green-and-yellow.
The protective devices
Beyond the main switch sits the busbar, a copper strip that carries the supply across the unit. Each protective device clips onto the busbar. There are three families used on UK domestic boards in 2026:
- MCBs (Miniature Circuit Breakers) trip on overload or short circuit. They do not provide RCD protection on their own.
- RCDs (Residual Current Devices) trip on earth fault, providing shock protection at 30mA. Older boards use one or two RCDs covering banks of circuits.
- RCBOs (RCD plus MCB combined) give every circuit its own dedicated RCD plus MCB. This is the modern standard plus what BS 7671 effectively pushes installers toward.
Some installs also include an AFDD (Arc Fault Detection Device) on circuits feeding sleeping accommodation or HMOs, plus a Surge Protection Device (SPD) at the supply. Both are now BS 7671 recommendations on a high-integrity board.
The outgoing circuits
Each existing circuit (ring final, lighting, cooker, shower, EV charge point, immersion, smoke alarms) terminates at its own protective device. The line conductor goes under the breaker terminal. The neutral lands on the neutral bar associated with that RCD bank (or onto a dedicated neutral terminal on an RCBO). The CPC lands on the earth bar. Every termination is torqued to the manufacturer's stated value, normally between 1.0 plus 3.5 Nm depending on conductor size.
Cables enter the enclosure through fire-rated grommets. The unit is metallic (almost always steel since the 2016 amendment to BS 7671) which provides additional fire containment compared to the older plastic units, which is why metal consumer units are now standard.
Typical consumer unit
install cost ranges
Pricing depends on board size, RCBO vs split-load, accessibility plus whether remedial work is needed. These are typical Milton Keynes plus Bedfordshire ranges.
Consumer Unit Replacement Cost Bands
Prices include parts, labour, EIC certification plus Building Control notification. Remedial work uncovered during testing (faulty cabling, missing bonding) is quoted separately.
From isolation to certificate
in one working day
A standard domestic consumer unit replacement runs to a 4 to 6 hour timeline plus a brief power-off window of 2 to 3 hours.
Isolate plus Survey
DNO contacted, pull-out fuse permission confirmed. Existing circuits identified, labelled then tested for safe disconnection.
Remove plus Mount
Old board removed. New metal enclosure mounted, tails dressed in. Main switch plus MET terminated first.
Wire Each Circuit
Every circuit conductor terminated to its RCBO or RCD bank. Torque-checked. Power restored circuit by circuit.
Test plus Certify
Full BS 7671 test sequence. Electrical Installation Certificate issued. Notification submitted to Building Control.
Four checks before
any consumer unit install
Part P registration
Only a Part P registered electrician can self-certify the work. Without that registration, the job has to be inspected by Building Control which is slower plus pricier.
Metal enclosure
Since the 2016 amendment, all domestic consumer units must have a non-combustible (metal) enclosure. Plastic units are no longer compliant on new installs.
RCBO over split-load
An RCBO board (one device per circuit) means a single fault only takes out one circuit not half the house. Worth the modest cost uplift on every modern install.
EIC certificate retained
Always get the Electrical Installation Certificate plus Building Control notice in writing. You will need both for sale, remortgage, EICR plus landlord compliance.
Consumer Unit Upgrades in Milton Keynes
C-Lec Electrical fits new consumer units to BS 7671 across Milton Keynes, Bedford plus the surrounding Bedfordshire area. Free quote, certified install, EIC plus Building Control notification handled in full.
RCBO board vs
split-load board
Both are compliant on a new install. Each is wired slightly differently. The choice changes how the house behaves when something faults.
Modern standard
- ●Each circuit has its own dedicated RCD plus MCB combined into one device.
- ●A fault on the kitchen ring only takes the kitchen ring offline. Lights, fridge plus router stay live.
- ●Wiring is cleaner inside the enclosure. Each circuit has its own neutral terminal on the RCBO body.
- ●Slightly higher parts cost. Stronger shock plus fault protection across the whole installation.
- ●Recommended on every new build, every full rewire plus every EV charger install.
Older compliant style
- ●One or two main RCDs cover banks of circuits. Each circuit also has its own MCB.
- ●A single earth fault can trip the whole RCD bank, taking out half the house at once.
- ●Lower parts cost. Simpler busbar layout inside the enclosure.
- ●Still compliant where each circuit is correctly grouped under the right RCD bank.
- ●Common in 2010 to 2018 installs. Often the board being replaced when homeowners ring us today.
For the wider context on consumer unit types, RCD vs RCBO, AFDDs plus when a board upgrade is genuinely needed, head back to our full guide to consumer units where every common homeowner question is answered in one place.
Back to the Consumer Units Guide
This article sits inside our complete Consumer Units knowledge base. The hub covers every topic from RCBOs plus AFDDs through to landlord requirements plus BS 7671 wiring regulations.
More on consumer
unit wiring
If you would rather understand the unit itself before getting into the wiring, our short explainer on what is a consumer unit covers every part of the box in plain language. Once you are ready to look at numbers, our pricing breakdown for how much to change a consumer unit sets out current 2026 ranges. For the formal rules, the dedicated consumer unit wiring regulations guide breaks down the BS 7671 sections that apply. If you need a board fitted in Milton Keynes, our consumer unit upgrades service page is the fastest route to a quote.