Replacing a consumer unit is one of the most common — and most regulated — jobs in domestic electrical work. This guide covers everything: when replacement is needed, current regulations, Part P requirements, typical costs, and what the job involves from start to finish.
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Written and reviewed by Andrew Moore, founder of Elec-Mate, against BS 7671:2018+A4:2026, IET Guidance Note 3 and the IET On-Site Guide.
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Not every consumer unit needs replacing. A well-installed, modern unit with adequate protection for the circuits it serves can remain in service for decades. However, several conditions make replacement necessary or strongly advisable.
If the property still has a rewirable fuse board (with porcelain or Bakelite fuse holders and fuse wire), it should be replaced. Rewirable fuses offer limited overcurrent protection, provide no RCD protection, and the fuse wire can be replaced with the wrong rating by an unqualified person. The board itself may also be a plastic enclosure, which no longer meets current regulations for domestic premises.
If the existing consumer unit has no RCD protection at all, it does not meet the current requirements of BS 7671, which require 30 mA RCD protection for almost all circuits in a domestic installation, including all socket-outlet circuits and cables concealed in walls. While there is no legal requirement to upgrade an existing installation retrospectively, the safety benefit of adding RCD protection is substantial — an RCD can prevent fatal electric shock and reduce the risk of electrical fires.
When new circuits are being added — for an EV charger, a kitchen extension, a garden office, or additional sockets — and the existing consumer unit has no spare ways, a replacement with a larger board is necessary. This is often combined with upgrading the RCD protection architecture at the same time.
Scorch marks, melted plastic, loose connections producing heat, or physical damage to the enclosure all require immediate replacement. These conditions indicate that the board has been subjected to fault conditions or has deteriorated to the point where it presents a fire risk. An electrician discovering these conditions during an EICR would typically classify them as C1 (Danger Present) or C2 (Potentially Dangerous).
Consumer units installed before January 2016 may have plastic enclosures. While there is no requirement to replace them solely because of the enclosure material, if the board is being replaced for any reason, the new unit must have a metal enclosure compliant with BS EN 61439-3. Many electricians recommend replacing older plastic boards proactively, particularly where they are mounted on combustible surfaces.
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A consumer unit change in 2026 must comply with BS 7671:2018+A4:2026 — the 18th Edition of the IET Wiring Regulations with Amendment 4. The key regulatory requirements are:
For full details on the regulatory framework, see the Consumer Unit Regulations guide.
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Replacing a consumer unit is always notifiable under Part P of the Building Regulations (England and Wales). This applies regardless of whether it is a like-for-like replacement, an upgrade, or part of a larger project. There are no exceptions — even if the old board is being replaced with an identical unit, the work is notifiable.
There are two routes to compliance with Part P:
The electrician is registered with an approved competent person scheme — NICEIC, NAPIT, ELECSA, BRE, or equivalent. The electrician self-certifies the work and notifies building control through the scheme. This is the most common route and avoids the need for a separate building control inspection. The scheme provider issues a building regulations compliance certificate to the homeowner.
If the electrician is not registered with a competent person scheme, the work must be notified to the local authority building control department before the work begins. A building control officer will inspect the completed work and issue a completion certificate. This route is more expensive (building control fees typically £200-£400) and takes longer.
A full Electrical Installation Certificate (EIC) is required for a consumer unit replacement. A Minor Works Certificate is not appropriate — the work involves the replacement of a distribution board, which is defined as requiring a full EIC in BS 7671. The EIC must include the design, construction, and inspection and testing sections, together with a complete schedule of test results for every circuit.
Arc Fault Detection Devices (AFDDs) are an additional layer of protection that detect dangerous electrical arcing — sparks caused by damaged cables, loose connections, or deteriorated insulation that can start fires. Unlike RCDs (which detect earth leakage) and MCBs (which detect overcurrent), AFDDs use electronic monitoring to identify the characteristic waveform signatures of series and parallel arcs.
Regulation 421.1.7 of BS 7671:2018+A4:2026 recommends the installation of AFDDs to BS EN 62606 in AC final circuits of a fixed installation to mitigate the risk of fire due to arc fault currents. The regulation uses "recommends" rather than "shall", so AFDDs remain advisory rather than mandatory — but A4:2026 is already the current edition of BS 7671 and this is live regulatory text. Many competent person schemes and building control bodies treat AFDD provision on bedroom and high-risk circuits as strong best practice.
Where AFDDs are fitted, on-completion verification is required: Regulations 421.1.7, 532.6, and 651.2(e) require the installer to confirm that each AFDD shows the correct operational indication and can be tested in accordance with the manufacturer's instructions. This confirmation must be recorded on the EIC schedule of inspections.
The cost of an AFDD RCBO is typically £80–£120 per circuit compared to £30–£50 for a standard RCBO. When specifying a consumer unit for a replacement, it is worth discussing AFDD provision with the customer — particularly for bedroom circuits and any circuits in locations with a higher fire risk such as roof spaces or areas with combustible structural materials.
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Start free trialThe cost of a consumer unit change depends on several factors: the size of the board, the type of protection (RCBO vs split-load), the condition of the existing wiring, and whether any additional work is needed.
6-8 ways, dual RCD, standard circuits
10-14 ways, individual RCBOs, SPD
12-16 ways, AFDDs on bedroom circuits
New tails, meter tails upgrade, earth rod
These prices include the consumer unit, all protective devices, labour, testing, the EIC, and Part P notification through a competent person scheme. VAT is typically included for domestic work. Prices vary by region — London and the South East tend to be at the higher end, while the North and Midlands are typically lower.
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Try it free for 7 daysA straightforward consumer unit replacement typically takes one day for a competent electrician. The process involves isolating the supply, removing the old board, installing the new board, reconnecting all circuits, testing every circuit, and producing the EIC. Here is what happens at each stage:
Before the day of the change, the electrician should survey the existing installation. This includes noting the number of circuits, identifying the cable sizes and types, checking the condition of the meter tails and earthing, and assessing whether any circuits need modification. This is also when the new board is specified and ordered.
On the day, the supply is isolated at the main fuse (by the DNO if a sealed cut-out is involved, or by the electrician if an isolator is available). The old board is disconnected — each circuit is carefully labelled and recorded before disconnection. The old board is then removed from the wall.
The new consumer unit is mounted and the meter tails connected. Each circuit is reconnected to its designated protective device (RCBO or MCB), following the design for the new board layout. The SPD is installed and connected. Earth and bonding connections are made up.
Torque tightening is essential. Every terminal — main switch clamp, RCBO/MCB screw terminals, neutral bar connections, and earth connections — must be tightened to the manufacturer's specified torque value. Under-torqued terminations are the leading cause of loose connections, overheating, and premature board failure. Use a calibrated torque screwdriver and consult the consumer unit manufacturer's data sheet for each terminal type.
Once all circuits are connected and the supply is restored, every circuit must be tested. The full testing sequence includes continuity of protective conductors (R1+R2), insulation resistance, polarity, earth fault loop impedance (Zs), prospective fault current (Ipf), and RCD testing on every RCD/RCBO.
The electrician completes and issues the Electrical Installation Certificate (EIC) with all test results. The circuit chart is printed and fixed inside the consumer unit door. The Part P notification is submitted through the competent person scheme. The homeowner receives copies of the EIC and the building regulations compliance certificate.
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Try it free for 7 daysRecord all existing circuits, cable types, cable sizes, and the condition of the meter tails and earthing. Check the DNO cut-out and confirm whether a temporary disconnection is needed. Photograph the existing board for reference. Specify the new consumer unit based on the number of circuits, RCD architecture (RCBO or split-load), and any additional requirements (SPD, AFDD, spare ways for future circuits).
Isolate at the main switch and, if necessary, pull the DNO fuse or arrange a temporary disconnection. Carry out safe isolation procedure — prove-test-prove using a GS38-compliant voltage indicator. Lock off and apply warning labels. Inform the occupants that the supply will be off for the duration of the changeover.
Disconnect all circuits from the old board, labelling each cable clearly. Remove the old board. Mount the new metal consumer unit. Connect the meter tails (typically 25mm² for 100A supply). Install the main switch, SPD, and all RCBOs or MCBs. Reconnect each circuit to its designated protective device following the design layout. Torque all terminals — main switch clamp, RCBO/MCB screws, neutral bar, and earth connections — to the manufacturer's specified values using a calibrated torque screwdriver. Under-torqued terminations are the most common practical failure mode on consumer unit replacements.
Restore the supply and carry out the full testing sequence on every circuit: continuity of protective conductors (R1+R2), insulation resistance at 500V DC, polarity verification, earth fault loop impedance (Zs), prospective fault current (PSCC and PEFC), and RCD operating time for every RCBO. Record all results in the schedule of test results.
Complete the Electrical Installation Certificate with all design, construction, and test data. Apply the circuit chart inside the consumer unit door. Submit the Part P notification through your competent person scheme. Issue copies of the EIC to the homeowner and retain your own copy for at least six years.
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