Consumer Unit Replacement Guide UK — 18th Edition Requirements and Pricing (2026)

When Should a Consumer Unit Be Replaced?

Several situations make a consumer unit replacement necessary or strongly advisable. Age is the most obvious trigger: a consumer unit that is older than 25 years — particularly if it contains rewireable fuses or older MCBs without any RCD protection — is unlikely to meet current standards and is a liability waiting to manifest. Rewireable fuse boards from the 1970s and 1980s are still found in service, and they should be treated as a C2 defect at minimum on any EICR.

An EICR that classifies the existing consumer unit as a C2 defect (inadequate protection) creates a direct obligation to replace it. This is the most common route to a consumer unit replacement job arising from a landlord EICR or a homeowner's pre-sale electrical inspection.

Other situations that typically necessitate or strongly indicate a consumer unit replacement include:

• Adding circuits that the existing board cannot accommodate, or upgrading the incoming supply amperage (typically from 60A or 80A to 100A)
• Damage to the existing board following flood or fire, even if it appears visually intact
• Installation of an EV charger, which requires a new dedicated circuit and is best served from a properly specified board with spare capacity
• A change in earthing arrangement — for example, switching from a TN-S to a TN-C-S (PME) supply — which requires the earthing and bonding to be reviewed and often upgraded

BS 7671 18th Edition Requirements for New Consumer Units

The single most important regulatory requirement for any new consumer unit installed in a domestic premises is that it must be in a non-combustible enclosure. In practice this means a metal enclosure — steel or similar — because plastic enclosures are combustible and are no longer acceptable for new installations.

This requirement was introduced by Amendment 3 to the 17th Edition of BS 7671 in 2015 and has been in force since January 2016. Amendment 2 (2022) to the current 18th Edition confirms and reinforces this position. The regulation exists because investigations into domestic fires identified consumer unit enclosures as a fire propagation risk in a small but significant number of cases — a fault arc inside a plastic board can ignite the enclosure itself.

RCD Protection Requirements

Every circuit in a domestic dwelling must have 30mA RCD protection. This is a fundamental requirement of Regulation 411.3.4 in the 18th Edition of BS 7671 and is not negotiable in a new or replacement consumer unit installation.

There are two main approaches to achieving whole-board RCD protection:

• Split-load consumer unit (dual RCD): the board is split into two groups of circuits, each protected by its own RCD. All circuits still get 30mA protection. This is the economical solution — the dual-RCD unit itself is cheaper and there are fewer individual components to install. The significant disadvantage is that if one RCD trips, it takes out every circuit on that half of the board — which can mean half the sockets and half the lighting going off simultaneously. Identifying the tripping circuit requires manually reconnecting circuits one at a time.
• All-RCBO consumer unit: each circuit has its own RCBO (Residual Current Circuit Breaker with Overcurrent protection), combining the functions of an MCB and an RCD in a single device. If one circuit trips, only that circuit is affected — every other circuit stays live. This is the superior solution from a discrimination and convenience standpoint, and it is increasingly specified as a minimum standard by social housing landlords, local authorities, and commercial clients.

Split-Load vs All-RCBO Consumer Units

The choice between a split-load dual-RCD board and a full RCBO board is one of the most common discussions on a consumer unit replacement job. Understanding the real-world differences helps both in scoping the job correctly and in advising clients.

Split-load advantages: cheaper unit cost (typically £120–£200 for the consumer unit), fewer individual components to install and test, and marginally faster to fit on a straightforward job. For a budget-conscious homeowner on an older property with stable circuits, a dual-RCD board does meet the regulatory minimum.

Split-load disadvantages: nuisance tripping affects multiple circuits at once, creating the potential for significant inconvenience and even safety issues (if half the lighting goes off on a staircase, for example). Fault-finding after a trip is slower and more disruptive for the occupant.

All-RCBO advantages: far better discrimination — a trip on the washing machine does not affect the freezer or the lights. No nuisance tripping of unrelated circuits. Increasingly required by social housing landlords, housing associations, and commercial clients as a contract condition. Often easier to certify cleanly because each circuit's protection is clearly identified and independent.

All-RCBO disadvantages: higher unit cost (typically £250–£450 for the consumer unit depending on size and brand) and a marginally higher component count. The cost difference narrows when labour is included, since the installation time difference between the two approaches is not dramatic on most domestic jobs.

Consumer Unit Sizing and Future-Proofing

Standard domestic consumer units are available in 10-way, 12-way, and 16-way configurations. The “ways” refers to the number of circuit breaker or RCBO slots, not counting the main switch. When sizing a replacement board, count the existing circuits, account for any that are being added at the same time (EV charger, solar PV inverter, heat pump), and then add spare ways.

The practical guidance is straightforward: install a larger board than you currently need. A 12-way board on a property that currently has 10 circuits costs very little more than a 10-way board but eliminates the need for another consumer unit replacement when the client fits an EV charger in three years. The same logic applies to a 16-way all-RCBO board on a large property — spare ways are cheap insurance against future changes.

For properties with a three-phase supply — more common in rural areas, large detached properties, and those connected to older commercial-type networks — a three-phase consumer unit (or distribution board) is required. Three-phase consumer units are larger, more complex to specify, and carry a higher price. If the property currently has a single-phase supply but three-phase is available at the street (e.g. in a rural area on an agricultural supply), it is worth discussing with the client whether upgrading to three-phase as part of the works makes sense for their future plans.

Pricing Consumer Unit Replacement

Consumer unit replacement pricing varies based on board specification, number of circuits, earthing and bonding condition, and access. The ranges below reflect 2026 market rates for straightforward domestic jobs in England outside London. Add 20–30% for London and the South East.

• Basic 10-way dual-RCD unit (fully installed, tested, EIC issued): £400–£600
• 12-way all-RCBO unit (fully installed, tested, EIC issued): £600–£900
• 16-way all-RCBO unit (fully installed, tested, EIC issued): £800–£1,200
• Three-phase distribution board (fully installed, tested, EIC issued): £1,000–£1,800

Several factors push a job toward the top of the range or beyond it: earthing improvements required (for example, upsizing the main earthing conductor or changing the earthing system type); main bonding work needed (absent or undersized bonding to gas and water services); a long isolation period due to tenanted property access constraints; rewiring of individual circuits found to be unsafe before they can be connected to the new board; or difficult consumer unit locations (high cupboards, cramped meter boxes, or split consumer unit arrangements).

Include all of this in your quote scope. A consumer unit replacement that turns into a half-day earthing and bonding job on top of the board change needs to be priced accurately upfront, or the conversation about additional cost becomes difficult mid-job.

Part P Notification

Consumer unit replacement is notifiable work under Part P of the Building Regulations in England and Wales. This means one of two things must happen: either the work is carried out by a registered member of a Competent Person Scheme (NICEIC, NAPIT, STROMA, or similar), in which case the scheme member self-certifies and notifies the relevant Local Authority Building Control (LABC) on the client's behalf; or the work is notified to Building Control before it begins, an inspector is involved, and a Building Control completion certificate is obtained after the work is done.

In practice, the second route is expensive and slow. Local authorities charge a Building Control fee for individual notifiable electrical jobs, and the process can take weeks. The entire reason that electricians join a Competent Person Scheme is to avoid this route — scheme membership enables the electrician to self-certify, which is faster, cheaper for the client, and keeps the paperwork entirely in the electrician's hands.

If you are carrying out consumer unit replacements without being registered with a Competent Person Scheme, either the client is paying Building Control fees on every job or the work is being done without any notification at all. Neither is acceptable. The Electrical Installation Certificate (EIC) you issue at the end of the job is not a substitute for Part P notification — both are required.

What to Check and Test During a Consumer Unit Replacement

A consumer unit replacement is not simply a like-for-like swap of the board. It is an opportunity — and a regulatory obligation — to verify the condition of the whole installation before connecting it to the new equipment. Key checks and tests include:

• Incoming supply condition: inspect the meter tails, their routing, and their condition. Tails must be sleeved or otherwise protected throughout their length where they pass through the consumer unit enclosure.
• Main bonding: check that main protective bonding conductors to gas and water services are present, correctly sized (minimum 10mm² for TN-C-S/PME supplies), and properly connected at both ends. Missing or undersized bonding is one of the most common defects found and must be addressed before the EIC is issued.
• Existing circuit condition: carry out insulation resistance tests on all circuits before connecting them to the new board. An insulation resistance failure on an existing circuit should be investigated and resolved before that circuit is energised from the new consumer unit.
• RCD test after installation: test each RCD or RCBO with the test button and with a purpose-made RCD tester to confirm correct operation and trip time within the 30mA / 40ms requirement.
• Electrical Installation Certificate (EIC): issue an EIC on completion, signed by both the designer and installer (which may be the same person) and the inspector. The EIC records the installation details, the test results, and confirms that the installation was inspected and tested in accordance with BS 7671.

Common Problems Found During Consumer Unit Replacement

No two consumer unit replacement jobs are identical, but certain problems appear with enough regularity that they are worth anticipating in every quote and every site assessment:

• Undersized main bonding conductors: properties that have had a supply upgrade from TN-S to TN-C-S (PME) over the years may still have 6mm² main bonding conductors from the original installation. TN-C-S requires a minimum of 10mm². This needs upsizing before the EIC can be issued — budget time and material for re-bonding to gas and water entry points.
• Absent bonding entirely: older properties and properties that have never had any electrical inspection work may have no main bonding at all. The gas and water bonds must be installed as part of the job. This is not optional and cannot be deferred.
• Unsafe DIY circuits by previous occupants: additional sockets, extra circuits, or modified ring mains carried out by non-qualified people are present on a meaningful proportion of domestic properties. These circuits must not be connected to the new consumer unit without investigation. Insulation resistance testing will often reveal the problem; further opening up of accessories or trunking may be needed to trace and assess the work before a decision can be made.
• Asbestos-backed consumer units: a small number of consumer units installed in the 1970s and 1980s used asbestos-containing backboards or enclosure materials. If you identify or suspect an asbestos-containing consumer unit, treat it as contaminated. Use appropriate PPE, do not drill or cut the board, and arrange proper licensed disposal of the removed unit. This is a health and safety obligation, not an optional precaution.

Talking to Clients About Consumer Unit Replacement

Clients rarely understand why they need a metal board, what the difference between an RCBO and an RCD is, or why the power needs to be off for most of the day. Taking ten minutes to explain the job properly before you start makes the day go more smoothly and reduces the chance of complaints or disputes after.

Key points to cover with clients before the job:

• Why a metal enclosure is required: explain that the regulation exists because of fire risk — if a fault arc occurs inside a plastic board, the enclosure itself can catch fire. A metal board contains and extinguishes the arc. This is a safety requirement, not a preference.
• Why all-RCBO is better: tell the client that an RCBO board means that if one appliance causes a trip, only that circuit goes off — not half the house. It is more convenient to live with, it is easier to diagnose faults, and it is increasingly the standard that letting agents and landlords expect on managed properties.
• What the disruption involves: a domestic consumer unit replacement typically requires four to eight hours with the power off. All sockets and switches will be checked during the testing phase. The client needs to be at home or have someone there to provide access, and should plan around having no power for the day. Fridges and freezers will be fine for a single day's isolation.
• What they receive at the end: an Electrical Installation Certificate documenting the installation and test results, a safer installation with proper RCD protection, and — where the work was notifiable — a Part P completion certificate that will appear in the property's building control history. This paperwork is relevant for conveyancing when the property is sold and should be kept safely.