Helpful video reference. John Ward (jwflame), a UK electrician based in Poole, Dorset, walks through a real EV charger job where the existing consumer unit had to go before the charger could be connected. His "EV CHARGER installation UK - WHY did we change the consumer unit?" is worth watching before you get survey quotes, because it sets honest expectations about what installers find and why an upgrade gets recommended. John covers the earthing and protective device choices in plain language.
1. Check what type of consumer unit you have
Open the consumer unit cover (the plastic cover over the breakers, not the metal enclosure itself) and look at what protective devices are fitted.
- Single RCD with MCBs: One large RCD at the left, with multiple MCBs to its right. Common in homes rewired in the 1990s and early 2000s. A single fault on any circuit trips the whole house.
- Split-load dual RCD: Two RCDs, one for each half of the board. Better protection, but every circuit shares an RCD with others. If there is a spare way on the appropriate side, a charger can sometimes be added here.
- Full RCBO board: Each circuit has its own combined MCB and RCD (RCBO). The most flexible and safest arrangement. Adding a circuit means adding one RCBO to a spare way.
- Rewireable fuse box: Ceramic fuseholders with fusewire. This always needs replacing before an EV charger is installed.
The age of the board matters too. A plastic consumer unit of any type that is more than 15 to 20 years old may have aged components, a label that no longer reflects the circuits, or no surge protection. The survey is the time to flag this.
2. Count the spare ways
A 7.4 kW home EV charger on a single-phase supply needs a dedicated 32 A radial circuit. That means one spare way in the consumer unit reserved for that circuit and nothing else.
Count the breakers currently fitted and compare with the total number of ways (slots) the board has. A 10-way board that already has 10 MCBs has no spare way. The options then are to upgrade to a larger board, or to install a separate EV consumer unit in the garage or at the charging point location, fed from the main board.
On a split-load board, the spare way needs to be on the correct half. EV charger circuits should ideally be on the RCD side that handles other heavy loads, not grouped with sensitive equipment that trips easily.
3. Confirm the earthing arrangement
This is the step that catches out the most homeowners - and many installers who do not take it seriously enough.
Most UK homes have a PME (Protective Multiple Earthing) supply, also called TN-C-S. The earth and neutral are combined in the street cable and separated at the meter. If the neutral conductor in the street develops an open circuit fault, the earth in your home can rise to a dangerous voltage. This is known as an open PEN fault.
BS 7671:2018 and the OZEV grant conditions both require open PEN fault protection before an EV charger is connected to a PME supply. This is usually a device built into the charger itself, or a separate detector installed alongside the supply circuit at the consumer unit. Without it, neither a competent electrician nor the charger manufacturer should proceed.
Some properties, particularly rural ones, have a TT supply with their own earth electrode in the ground. TT supplies do not have the same open PEN risk, but they need a sound earth electrode and appropriate RCD protection for the charger circuit.
4. Assess the incoming supply capacity
Adding a 7.4 kW charger draws 32 A on a single phase. Your incoming main fuse (usually 60 A, 80 A or 100 A sealed in the cutout on the wall near the meter) sets the absolute limit for the whole property.
The electrician does a diversity calculation: total the maximum simultaneous loads across all your circuits and compare with the supply capacity. In most homes this is fine because not every circuit runs at full load at the same time. But in a property that already has electric heating, an electric shower and a high-power hob, adding 32 A of continuous EV charging can push the mains fuse. The network operator (not you, not the installer) controls the supply rating.
5. Check the meter tails and main switch
The meter tails are the thick cables running from your meter to the consumer unit. Old installations sometimes have 16 mm2 tails where the current board and supply rating would warrant 25 mm2. The main switch (usually 100 A in a modern installation) may also be undersized if it was installed when the board was originally fitted to a lower-rated supply.
Neither of these stops an EV charger going in by itself, but if the tails or switch are marginal, the electrician should note it on the job report and discuss it with you.
6. The upgrade decision: connect or replace?
After the survey, the electrician can give a clear recommendation.
Connect to existing board if: the board is a split-load or RCBO type in sound condition, a spare way is available on the appropriate side, the earthing is confirmed, and the supply capacity is adequate.
Replace the board if: no spare ways remain, the board is a single-RCD type or a rewireable fuse box, the board is in poor condition, or the earthing arrangement is unclear or unsatisfactory.
Replacing the consumer unit at the same time as fitting the EV charger is often cost-effective because the electrician is already on site and the job is notifiable either way. The combined cost is usually less than having the board changed as a separate job later.
When to call us
Richard covers EV charger installations across Sandwich and east Kent. If you are unsure what type of board you have, or whether your supply can handle a 7.4 kW charger, book a survey first. The survey looks at everything above, gives you a clear written quote, and tells you exactly what the job involves before any money changes hands.
Planning an EV charger in Sandwich or east Kent?
Richard carries out EV charger surveys and installations, including consumer unit upgrades where needed. OZEV-eligible installations, certified and documented.
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