Many smart home projects fail not because the technology doesn't work but because the electrical first fix wasn't designed for it. Standard UK domestic wiring has evolved for traditional switches and simple circuits. Smart home devices, particularly smart switches and dimmers, have different wiring requirements. Getting this wrong during first fix means either an expensive rewire or compromising on the smart home setup you wanted.
This guide is designed to help you have an informed conversation with your electrician before first fix begins, so the wiring is right from the start.
The Neutral Wire Problem
This is the most common issue. Traditional UK two-way switch wiring uses a switch line and a common, but does not provide a neutral wire at the switch position. Most smart switches and dimmers require a neutral wire to power their electronics continuously, even when the light is off.
There are workarounds: some smart switches (Philips Hue, Shelly, Sonoff) offer no-neutral versions that work with a small amount of current flowing through the lamp (the so-called "ghost current"). These work with LED bulbs in many cases, but can cause flickering with some LED models and incompatibility with others. They're not as reliable as neutral-wire versions.
The clean solution is to wire all switch positions with a neutral wire. In new build or first-fix work, this is straightforward: run three-core and earth cable (which includes a neutral) to switch positions instead of the standard two-core. Cost impact is minimal during first fix. Retrofitting after plastering is expensive.
Tell your electrician explicitly: "I want neutral wires run to all switch positions." If they look blank or confused, you need a different electrician for this part of the work.
Lighting Circuit Design
Standard UK lighting circuits run multiple lights in a loop from the consumer unit, with switches wired back from each light. For smart lighting, there are two approaches:
Smart bulbs (Philips Hue, LIFX, Innr). Standard wiring. The intelligence is in the bulb. The switch sends constant power to the bulb, and control is via an app or smart hub. Limitation: if someone turns the light off at the physical switch (cutting power), the bulb can't be controlled remotely until power is restored. Use smart switches that send signals but maintain power, or smart rotary dimmers compatible with your bulb brand.
Smart switches or dimmers at the switch position. Standard (non-smart) bulbs or downlights, controlled by a smart switch or dimmer module. Requires neutral wire at the switch as discussed. The switch handles the intelligence. This is generally more reliable for whole-house installations than smart bulb approaches.
For a new build or substantial renovation, smart switches with neutral wires and conventional fittings is the more robust approach. It uses the fittings you've specified (and can upgrade or replace without rewiring), and the switches operate independently of which brand of smart home system you use.
CCTV and Smart Doorbells
Wired security cameras are significantly more reliable than wireless. If you're doing building work, run Cat6 network cables to the planned positions of any external CCTV cameras. PoE (Power over Ethernet) cameras draw both power and data over a single Cat6 cable, simplifying installation. Wireless cameras need power sockets nearby or battery replacement, and Wi-Fi reliability outdoors can be poor.
Smart video doorbells (Nest, Ring, Arlo) come in both wired and battery versions. Wired versions use the existing doorbell transformer circuit. They typically require 8-24V AC. If your existing doorbell wiring is old or the transformer is undersized, some wired video doorbells won't work reliably. During first fix, run a 2-core low-voltage cable from the proposed doorbell position to the location of the transformer or a new junction, and check the transformer output voltage is appropriate for the device you intend to install.
EV Charger Wiring
If you don't have an EV now but might in the next five to ten years, the time to run the cable infrastructure is during building works. A 7kW home charger (the standard domestic charging speed) requires a dedicated 32A radial circuit from the consumer unit to the garage or parking area. The cable is typically 6mm2 twin and earth.
Running this cable while walls are open and groundworks are in progress costs perhaps £300-£500 in additional materials and labour. Running it retrospectively through finished walls, possibly under a patio, costs significantly more. Even if you cap the cable off at both ends for now, the infrastructure is there when you need it.
Consumer Unit Planning
Smart home additions create additional circuit requirements: EV charger, ASHP, solar PV inverter, hot tub, home office circuits, garden circuits. Plan the consumer unit size early. A consumer unit specified for a standard domestic load and then asked to accommodate all of these additions will run out of ways quickly.
Install a consumer unit with spare ways. A unit with 20 ways when you currently need 14 is trivially more expensive than a 14-way unit during installation, and may save a board changeover later. Also consider whether an energy monitoring consumer unit or CT clamp monitor is worthwhile: it lets you track per-circuit consumption and optimise your energy use.
Draw a room-by-room socket and switch plan before first fix. Go through every room and think about where you'll put furniture, where you'll use screens, where charging cables will run, and where you might want speaker cables, network points, or future control panels. The pain of this exercise is trivial compared to adding sockets to finished walls.
Data and Low-Voltage Points
Beyond standard electrical work, think about these low-voltage points during first fix:
- USB charging points in bedrooms, kitchen, and study (either integrated socket inserts or nearby USB chargers wired to a fused spur)
- Smart thermostat positions: a backplate with live, neutral, and switched connections for a Nest, Tado or Honeywell smart thermostat
- Outdoor socket circuits (RCD protected, rated for outdoor use) for garden equipment and external lighting
- Loft light and socket for future equipment (solar inverter, storage batteries, networking equipment)
- Low-voltage wiring for video doorbell intercom systems if you're planning a lobby or multi-unit setup
All of these are minor cost additions during first fix. All of them are disproportionate cost additions in retrospect.