Fuse board replacement and consumer unit upgrades across London

The consumer unit — often called the fuse board or fuse box — is the distribution board that receives the incoming electricity supply from the meter and splits it into individual circuits: ring finals for sockets, radial circuits for fixed appliances, lighting circuits, and dedicated circuits for the cooker, shower, and EV charger. Each circuit is protected by either a miniature circuit breaker (MCB) or, in a modern board, a residual current circuit breaker with overcurrent protection (RCBO).

When a fault occurs — an overloaded circuit, a short circuit, or a ground fault — the relevant protective device operates and disconnects only that circuit, leaving the rest of the installation energised. In an older board protected only by rewireable fuse wire, this protection is slower, less precise, and provides no protection against electric shock.

The 18th edition wiring regulations (BS 7671:2018) and its amendments set the current baseline for electrical installations in the UK. A consumer unit that does not meet these requirements is not automatically illegal to own — existing installations are not retrospectively required to upgrade — but any new installation, replacement, or notifiable alteration must comply. More practically, a non-compliant board will generate C2 observations on an Electrical Installation Condition Report (EICR) that lenders, insurers, and conveyancers increasingly require before approving a mortgage or completing a sale.

Three generations of consumer unit design are still in service across London properties. The oldest — rewireable fuse wire boards in wooden or Bakelite enclosures — date from the 1960s and 1970s. These offer no RCD protection whatsoever: if you touch a live conductor, there is nothing in the board to disconnect the supply fast enough to prevent a fatal shock. The fuse wire does protect against sustained overcurrent, but it operates far too slowly for electric shock protection and the correct fuse rating is easily defeated by replacing blown wire with a higher-rated substitute.

The second generation — plastic consumer units with a single split-load RCD — was the standard installation from roughly the mid-1990s through to the early 2010s. These provide RCD protection across all circuits, but group them onto one of two RCDs. A single fault — a failing light fitting, a damp socket, a deteriorating appliance — trips the RCD and kills every circuit on that side simultaneously: half the sockets in the house, all the downstairs lighting, the refrigerator, the burglar alarm. This nuisance tripping is not merely inconvenient; it creates pressure to bypass the protection rather than identify the fault.

A third deficiency in all consumer units installed before 2022 is the absence of a surge protection device (SPD). Amendment 2 to BS 7671:2018 introduced a requirement for SPDs on all new installations in dwellings. Transient overvoltages from nearby lightning strikes or switching events in the distribution network can destroy connected electronics in milliseconds. An SPD clamps these transients before they reach circuit wiring and connected equipment.

In most London leasehold flats, the consumer unit is within the demised premises and replacement falls under the leaseholder's right to carry out internal repairs and improvements. However, many leases contain a clause requiring the leaseholder to obtain the freeholder's or managing agent's written consent before carrying out structural alterations or major electrical work.

Whether a consumer unit replacement qualifies as an "alteration" under your lease depends on the specific wording. Consumer unit replacements are not structural, do not alter the building fabric, and in most leases are treated as like-for-like electrical maintenance. That said, we recommend reviewing your lease and, where there is any doubt, obtaining written consent from the freeholder or managing agent before works commence. This protects you from any future dispute and provides a paper trail alongside the Part P notification.

Where the meter and incoming supply equipment is located in a communal area, the freeholder's consent and often a communal area permit will be required before any work near the incoming supply. We can advise on this during the survey visit.

Part P of the Building Regulations (England) requires that notifiable electrical work in dwellings is either carried out by a registered competent person scheme member or notified to the local authority building control department. Consumer unit replacement is explicitly listed as notifiable. Failure to notify means the work has no Building Regulations status — it is technically an unauthorised building works.

The practical consequence emerges at the point of sale. Your conveyancer will raise a requisition for any electrical installation certificates or Building Regulations completion certificates for work carried out since 2005. Absent documentation for a consumer unit replacement is a red flag that can delay or abort a sale. A buyer's surveyor noting an undocumented replacement board can lead to a retention on completion funds until the issue is regularised — a process that typically involves an inspection and fee to the local authority.

As NICEIC-registered electricians, we self-certify and submit the Part P notification to your local authority building control on your behalf. You receive the Electrical Installation Certificate and the Building Regulations completion certificate as part of the standard job package — no additional steps required.