Helpful video reference. The video above from Vartia Electrics shows the installation of an isolation switch and dedicated EV board in a UK domestic property. The channel uses correct UK wiring colours, isolates properly at the consumer unit and discusses the Wylex enclosure used for the EV board. Worth watching before the job to understand how the two units relate to each other.
1. Choose the right EV board
A dedicated EV board is typically a small consumer unit with a 100A or 63A main switch and one or two ways for circuit breakers. Common choices are a Wylex NHXS1100 or similar single-way unit for a single charger, or a two-way board if a future circuit is anticipated.
The board must be rated for the prospective fault current at the point of installation. Check the Ze value at the supply origin - on a typical UK TN-C-S supply this is often 0.2 to 0.35 ohms. The PSCC at that point determines the minimum short-circuit rating required for the board and its breakers.
2. Plan the supply route and cable size
The EV board is usually fed from a switch fuse isolator unit positioned near the main consumer unit, which in turn is fed from the meter tails. The sub-main cable between the switch fuse and the EV board is typically 16mm² or 25mm² twin-and-earth, depending on the length of the run and whether it passes through insulation or enclosed spaces.
Use the On-Site Guide current-carrying capacity tables and correction factors to confirm the cable can carry the design current under the actual installation conditions. A 25mm² cable clipped direct can carry around 110A before correction - more than enough for a 32A charger circuit, but the correction factors for enclosed spaces or bundled cables can reduce this significantly.
3. Isolate the upstream supply safely
Before connecting anything at the main consumer unit or switch fuse, achieve safe isolation. Switch off at the consumer unit main switch, lock out if possible, and test at the intended connection point - line-to-neutral, line-to-earth and neutral-to-earth with a calibrated voltage tester. All three must read zero before you touch any conductor.
4. Position and fix the EV board
Mount the EV board on a non-combustible surface - plywood backed with fire-retardant paint or directly on a masonry wall. Position it as close to the charger as the cable route allows, and ensure the cable entry knockouts line up with the incoming supply direction. Fix it level and securely with the correct number of screws for the enclosure size.
5. Run and connect the feed cable
Install the sub-main cable from the switch fuse to the EV board. Clip it at regular intervals, protect it where it passes through holes in joists or walls, and route it to avoid safe zones where other services run. At the EV board end, connect line, neutral and earth to the incoming terminals and torque to the manufacturer's specification. At the switch fuse end, connect to the load side terminals in the same way.
6. Fit the charger circuit RCBO
Inside the EV board, fit the RCBO for the charger circuit. BS 7671 Section 722 requires RCD protection for EV charger circuits, and the type of RCD required depends on the charger. Most modern AC home chargers (7kW, 32A) require at minimum a Type A RCBO, which detects both AC and pulsating DC fault currents. Some chargers - particularly those without a built-in DC fault sensor - require a Type B RCBO. Check the charger manufacturer's installation requirements before ordering the RCBO.
The RCBO should be rated at 32A and have a 30mA sensitivity for EV circuits unless the charger specifies otherwise.
7. Check earthing and open PEN fault protection
On a TN-C-S (PME) supply, BS 7671 Section 722.411.4.1 requires open PEN fault protection at EV charger circuits. If the PEN conductor in the DNO's supply cable breaks, the earth in a PME installation can rise to line voltage. An open PEN detection device disconnects the charger supply if this happens, protecting anyone touching the charger body or a vehicle being charged.
The open PEN protection device is typically built into modern smart chargers, but if it is not, a separate open PEN protection relay must be fitted in the EV board. Confirm which arrangement the charger uses before commissioning.
8. Test, commission and document
Carry out the required tests: insulation resistance between live conductors and earth on the completed circuit, continuity of the circuit protective conductor, earth fault loop impedance (Zs) at the charger end, and RCD operation time under BS EN 61008. Record all results on the Schedule of Test Results attached to the Electrical Installation Certificate.
Notify the installation through your competent person scheme (NAPIT, NICEIC or equivalent). Register the charger with the manufacturer if the warranty or OZEV grant requires it. Leave copies of the certificate with the homeowner.
When to call us
Richard installs dedicated EV boards and charger circuits across east Kent as part of a complete EV charger installation package. If you are planning a home charger and want the electrical infrastructure done properly, get in touch.
EV charger wiring in Sandwich and east Kent
Richard designs and installs the complete electrical infrastructure for home EV chargers, including switch fuse isolators, dedicated EV boards and charger circuits.
Contact Richard