Electrical Specification in London Renovations: First Fix, Consumer Units, and EV Charging

Electrical work in a London renovation is governed by BS 7671 (the IET Wiring Regulations), and all notifiable works must be carried out by a Part P registered electrician who can self-certify to Building Control. The electrical specification determines what is possible in a completed building — circuits that are not run at first fix cannot be added without opening walls. This makes pre-construction electrical planning one of the highest-leverage activities in the entire project.

This guide covers what a complete electrical specification includes, how to think about future-proofing, and the common decisions that are worth getting right at design stage.

The consumer unit (fuse board)

The consumer unit is the heart of the electrical installation. It houses the main switch, RCDs (residual current devices), and MCBs (miniature circuit breakers) for each circuit. In any significant renovation, the consumer unit should be reviewed and typically replaced if it is more than 20–25 years old or if it does not meet current BS 7671 requirements.

Current requirements: since the 18th Edition of the Wiring Regulations (2018), all new consumer units must be metal-clad (fire-resistant) when installed in a domestic property. Plastic consumer units are no longer compliant for new or replacement installations.

RCD protection: all circuits in a domestic installation require RCD protection. The preferred configuration is dual RCD (split load board) or RCBO (residual current circuit breaker with overcurrent protection) per circuit. RCBOs are more expensive but superior: if one circuit trips, only that circuit goes down rather than half the board.

Circuit count: plan for expansion. A consumer unit with no spare ways at practical completion will cause problems within years as technology requirements change (EV charging, additional circuits for outbuildings, smart home systems). Specify a board with at least 4–6 spare ways beyond current circuits.

Socket and outlet specification

Sockets are the most frequently moved or added item in post-completion renovation regret lists. Planning them carefully at first fix costs nothing extra; moving them after plastering is expensive.

Principles for socket layout:

• —Every usable wall in a bedroom should have double sockets within reach of where furniture will be placed. For a typical bedroom, this means sockets at both sides of the bed position, on the wall opposite the bed, and adjacent to a desk or dressing table position — minimum 4 double sockets per bedroom.
• —Living rooms and open-plan spaces: sockets on all walls, at intervals of no more than 3m, plus floor boxes in the centre of large rooms if a sofa or island seating arrangement is anticipated.
• —Kitchens: worktop-height sockets (150mm above worktop level) at intervals of no more than 600mm along working runs, plus sockets inside appliance housing (for integrated fridge, dishwasher, and washing machine power supply), plus a dedicated socket for the boiling water tap unit if specified.
• —Home office: minimum 4 double sockets at desk height; consider a floor socket for a central desk.

USB sockets: USB-A and USB-C integrated socket modules are standard in quality renovations. Specify at bedside positions, kitchen worktop positions, and home office positions at minimum.

Outdoor sockets: weatherproof double sockets at the rear of the property (near the terrace or garden area) and at the front (for seasonal lighting, car cleaning). These require RCD protection and appropriate IP-rated enclosures.

Lighting circuits

Refer to the lighting design specification for detailed circuit planning. Key electrical specification points:

Dimmer compatibility: specify trailing-edge (capacitive/reverse-phase) dimmers for all LED lighting circuits. Leading-edge (TRIAC) dimmers cause flickering and buzzing with LED drivers. Confirm the dimmer model is on the luminaire manufacturer's approved list — not all trailing-edge dimmers are compatible with all LED drivers.

Circuit labelling: all lighting circuits must be clearly labelled in the consumer unit and on a circuit schedule. This seems obvious but is routinely omitted by electricians who expect to remain familiar with the installation. A labelled schedule saved in a property file is essential for future maintenance.

Emergency lighting: not typically required in domestic properties but worth considering for deep basement conversions where the only escape route could be through an unlit stairwell in a power cut. Battery-backed emergency luminaires are a low-cost provision.

Dedicated circuits

The following items require dedicated circuits (a circuit that serves only that appliance):

• —Electric shower or bath pump: 10.5kW shower requires a 10mm² cable and 45A MCB
• —Induction hob (70cm): typically 7.2kW, requiring 10mm² cable and 40A MCB
• —Double oven: typically 3–6kW; dedicated 6mm² circuit
• —Tumble dryer: dedicated 2.5mm² 16A circuit
• —EV charger (see below)
• —MVHR unit: typically a dedicated spur
• —Hot tub or swim spa (if applicable): requires specialist electrical design

EV charging

EV charging provision is now standard in any quality London renovation and is becoming a Building Regulations requirement in certain scenarios (new builds and major renovations with off-street parking under Part S).

Options:

• —3-pin 13A socket (granny charger): adequate for overnight charging of most EVs (provides approximately 8–10 miles of range per hour). No specialist installation required — any outdoor socket works. Slow, but functional for low-mileage users.
• —7kW home charger (Mode 3, Type 2): the standard home EV charging solution. Provides approximately 30–35 miles of range per hour. Requires a dedicated 7kW (32A) circuit in 6mm² cable from the consumer unit, with a 40A MCB and appropriate RCD protection. An OZEV-approved smart charger is required to qualify for the OZEV grant (currently up to £350 for eligible properties). Smart chargers communicate with the grid for off-peak scheduling.
• —22kW three-phase charging: only relevant where three-phase supply is available. Most London residential properties have single-phase supply; a three-phase upgrade requires DNO (Distribution Network Operator) application and significant cost.

For any property with off-street parking, run a 6mm² cable to the parking position at first fix even if EV charging is not being installed immediately. The cable cost at first fix is trivial; the disruption to install it later is not.

Consumer unit location and meter position

In London's terraced housing, the electricity meter is typically near the front door, in a hallway cupboard, or in a communal area (for flats). The consumer unit should be accessible but not prominent — a meter/consumer unit cupboard with ventilation slots in the door is the standard solution.

Do not locate the consumer unit in a bathroom, kitchen (in a position where it could be subject to steam or splashing), or in a position accessible to children without adult supervision. A loft installation is acceptable if there is a permanent loft ladder and adequate light.

Smart home electrical infrastructure

If a smart home system (Lutron, KNX, Control4, or simpler Zigbee/Matter-based systems) is being specified, the electrical infrastructure must support it:

• —Wired smart systems (KNX, Lutron RadioRA): require dedicated bus cable (2-core screened for KNX, or proprietary Lutron cable) run from each switch position to a central hub location. This is entirely separate from the power wiring and must be specified to the electrician at first fix.
• —Wireless smart systems (Hive, Lightwave, Zigbee): no additional cable required, but backbox depth must accommodate smart switch modules (typically 35mm deep versus 25mm for standard switches).

Specifying the smart home system after first fix is a common and expensive oversight. The cable cost at first fix is negligible; the disruption to retrofit it is not.

Electrical installation condition report (EICR)

For any renovation of an existing property, an EICR should be commissioned before work begins to identify pre-existing deficiencies. The EICR establishes what is present, what requires immediate rectification, and what can be retained. It provides a baseline that protects the client (and the contractor) if disputes arise about pre-existing conditions.

On completion of the electrical works, the installing electrician issues an Electrical Installation Certificate (EIC) covering the new and altered circuits. This document should be retained with the property records — it is required for future sale and for insurance purposes.