The electrical installation is the nervous system of a prime London renovation — and, like a nervous system, it is almost entirely invisible once the house is complete. The quality of the specification determines whether the client spends the next twenty years with reliable power, excellent light, and seamless technology, or with nuisance trips, inadequate sockets, and systems that cannot be extended without opening finished walls. Getting it right means designing the system before first fix, specifying the right products, and understanding the relationship between the electrical installation and every other system in the house.
The Design Sequence
Electrical design on a prime renovation should begin at RIBA Stage 3 (Developed Design), in parallel with the mechanical services design and the lighting design. The three are closely interdependent: the lighting designer specifies the luminaires and control zones; the mechanical engineer specifies the plant loads and controls wiring; the electrical engineer coordinates both into a single distribution design and produces the load schedules, circuit layouts, and cable routes.
On a prime London townhouse, the electrical engineer's deliverables should include: a load schedule (total connected load and calculated maximum demand), a distribution board schedule (circuits, ratings, protective devices), a lighting circuit layout (tied to the lighting designer's zones), a power circuit layout (socket positions, appliance connections, EV charger provision), a data and communications layout, and a specification for the switchgear, wiring, and containment. These drawings are the basis for the tender to specialist electrical contractors and for the Building Regulations Part P compliance documentation.
Distribution and Metering
Incoming supply: A prime London townhouse typically has a single-phase 100A supply from the DNO (Distribution Network Operator). This is adequate for a house without a large EV charger or significant electrical heating load; a house with two EV chargers (7.4kW each), an air source heat pump (10–15kW), and underfloor heating in multiple zones may approach or exceed the 100A limit, triggering a supply upgrade application to the DNO. DNO upgrade lead times in London can be six to twelve months — this must be identified and applied for early.
Main distribution board (MDB): The MDB should be a modern consumer unit (Type 2 surge protection device included, as required by BS 7671:2018+A2:2022) with sufficient ways for all circuits plus 25% spare capacity for future additions. In a large townhouse with multiple floors and many circuits, a dual-board arrangement (main MDB at basement level, sub-distribution board at upper floors) avoids excessively long cable runs and simplifies future maintenance. All boards should be in accessible locations — meter cupboards, plant rooms, or utility areas — not in finished joinery where access requires a contractor.
RCD and RCBO protection: Modern wiring regulations require RCD (Residual Current Device) protection on all circuits; the most resilient approach uses individual RCBOs (combined MCB and RCD) for each circuit rather than shared RCDs across multiple circuits. With shared RCDs, a fault on any one circuit trips all circuits on that RCD — a nuisance in any room, unacceptable in a kitchen or bedroom. Individual RCBOs cost more but make fault-finding faster and eliminate nuisance tripping.
Cable Routes and Containment
In a prime renovation, all cables are concealed — in walls (chased into plaster), under floors (in conduit within the screed or timber floor), or above ceilings (in accessible ceiling voids). Surface-run cables in trunking are not acceptable in a finished prime interior.
The cable routes must be agreed and confirmed before first fix — the electrician must know where every cable runs before chasing walls or running under floors, because changing cable routes after plastering or screeding is extremely disruptive. A cable schedule that documents every circuit's route, in sufficient detail for any competent electrician to run the cable without interpretation, is the right deliverable.
Conduit in screed: All cables in concrete or sand-cement screed should be in conduit (rigid PVC or corrugated plastic), not loose in the screed. Conduit allows cables to be withdrawn and replaced without breaking out the screed — a significant practical benefit in a house that will be occupied for decades. The conduit must be sized for the cables it carries plus a draw-wire for future additions.
Low-voltage data and AV cabling: Data, AV, and control cabling (Cat 6A for data, coaxial for AV distribution, KNX or similar for controls) should be run in separate containment from mains power cables. Physical separation reduces interference and simplifies future changes. In a KNX or similar smart controls installation, the controls wiring is a star topology from the distribution board to each device — a fundamentally different routing from the ring/radial topology of power circuits — and must be planned separately.
Lighting Circuits
Circuit zoning: Lighting circuits in a prime renovation are zoned by room and by control group within rooms — not by floor. A room with ceiling lighting, wall lighting, and table lamp circuits fed from switched outlets may have three or four separate lighting circuits. This granularity is necessary to support scene-based lighting control (Lutron, KNX) where each circuit is independently dimmable.
Dimmer compatibility: LED luminaires require TRIAC or leading-edge dimmers that are compatible with the specific driver in the luminaire. Not all LED drivers are dimmable; not all dimmable LED drivers are compatible with all dimmer types. The lighting designer, luminaire supplier, and electrical engineer must agree on the dimmer specification before procurement — a circuit full of luminaires that buzz or flicker at low dim levels because the driver and dimmer are incompatible is an expensive and difficult problem to fix in a finished interior.
Emergency lighting: In a large townhouse or any building undergoing a change of use, Building Regulations and the fire risk assessment may require emergency lighting on escape routes. This is typically self-contained emergency LED fittings (with integral battery and self-test facility) at the head and foot of each staircase and at escape route junctions.
Power Circuits
Socket provision: Prime residential design should provide generous socket provision — the most common client complaint in a newly completed renovation is insufficient sockets. The standard for a prime London renovation: a minimum of four double sockets per habitable room, with additional circuits for specific appliances (kitchen worktops, home office, dressing room). Island units in kitchens should have flush-mount pop-up sockets. All sockets in a prime interior finish should be in a consistent, specified finish (brushed brass, polished nickel, or matt black are common choices in prime renovations) to a named brand (Hamilton, Wandsworth, Forbes & Lomax, or equivalent).
Dedicated appliance circuits: Large appliances require dedicated circuits: oven (32A or 45A cooker circuit), dishwasher, washing machine, tumble dryer, wine fridge, ice maker. These should be identified in the electrical design and included in the load schedule; adding them as afterthoughts during fit-out may require additional circuits from an overloaded board.
EV charging: A prime renovation should be futureproofed for EV charging even if the client does not currently own an electric vehicle. This means a 32A, 7.4kW single-phase circuit from the distribution board to the garage or parking space, with a 32A isolator at the parking end, ready for a charger to be connected without additional electrical work. If there is space for two vehicles, install two circuits.
Smart Controls Integration
A KNX or Lutron-based smart home system fundamentally changes the electrical installation. Instead of conventional light switches (which directly switch the circuit), the installation uses actuators (relay modules that switch the circuits) controlled by pushbutton panels (which send commands to the actuators via the bus). The pushbutton panels require a KNX bus cable (typically YCYM 2×2×0.8mm) from each panel to the nearest bus junction; the actuators sit in the distribution board or in local distribution points.
This topology means the electrical first fix is more complex and requires more coordination: the electrician must install not only the power and lighting circuits but also the bus cabling to every switch position. The controls programmer (the KNX or Crestron integrator) must define the system architecture before first fix so the electrician knows which devices are connected to which actuators.
The payoff is a system that can be reprogrammed without opening walls: if the client wants a different lighting scene, or wants to add automation (time-based, occupancy-based, or scene-triggered), the programmer can deliver it via software without physical alteration.
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