EV Charger Installation

The part that happens before the drill comes out

Fitting a charge point to a wall is straightforward. Establishing that the supply can carry it, and that the earthing arrangement is safe for a substantial metal object being touched outdoors, is the actual work.

A domestic charge point is an unusual load. It draws close to its maximum for hours at a time, often overnight, often unattended. Nothing else in a house behaves like that, which is why the design rules for charge points are stricter than for a socket of the same rating.

Load assessment

Every installation starts with what the supply can carry. That means the rating of the main service fuse, the size and condition of the tails and consumer unit, and an assessment of maximum demand across the existing installation with diversity applied — the recognition that the shower, oven, immersion and kettle are unlikely to run flat out simultaneously.

A charge point does not benefit from diversity in the same way. It is treated as a continuous load, because that is what it is.

Where the sum exceeds what the service can supply, there are three routes:

• Load management. A current transformer on the incoming supply tells the charge point how much headroom is left, and the unit throttles down when the house demand rises. This is the usual answer and it works well.
• A reduced charging rate. Limiting the unit to a lower current permanently. Simple, and often perfectly adequate for overnight charging.
• A supply upgrade. The network operator’s job, not ours, and it carries its own cost and timescale.

Earthing and PEN fault protection

Most homes are supplied under a PME arrangement, where the earth for the installation is taken from the incoming combined neutral and earth conductor. It is a sound system with one specific failure mode: if that conductor breaks somewhere in the network, the earthed metalwork in the property can rise to a dangerous voltage relative to true earth.

Inside a house, main bonding keeps everything at the same potential and the risk is contained. Outside, standing on soil or a wet drive with a hand on a charging car, it is not. The regulations respond to this by requiring either a device that detects the voltage excursion and disconnects the charge point, or an installation method that gives the charge point its own earth electrode independent of the supply.

We establish the earthing arrangement at survey rather than assuming, because the answer changes the specification and the cost.

Smart charging requirements

Charge points sold for private use in the UK must meet smart charge point regulations. In practice that means default charging schedules that sit outside peak demand periods unless you deliberately override them, a randomised start delay of up to several minutes to stop thousands of cars switching on at once, retention of settings through a power interruption, and measurement and security requirements on the unit itself.

None of this restricts you in daily use — you can override a schedule whenever you want. It does mean that commissioning involves getting the unit onto your network and into your account, which is worth ten minutes of your time on the day.

Working with solar and storage

Where there is an array, the useful setting is the one that only charges from surplus. The charge point watches the export at the meter and matches it, ramping up on a bright afternoon and backing off when a cloud passes or the oven goes on.

It is genuinely useful, and it is genuinely slow. A modest array on a mixed day may deliver only a few kilowatt-hours into the car. Where there is a battery as well, the sensible configuration is a hierarchy: house first, then car from surplus, then battery, then export — or a different order, depending on your tariff. We set that with you at commissioning.