PEN fault protection and earthing for EV chargers

Earthing is the part of an EV installation most people never think about, and one where installers sometimes add cost. This guide explains the problem it solves and the three ways installers deal with it, so you can judge a quote.

What a PEN fault is

Most UK homes have PME earthing (protective multiple earthing, also called TN-C-S). The supply cable uses a single combined conductor for neutral and earth, called the PEN conductor, and your installation’s earth connects to it at the incoming supply. That works well and is why a normal house is safe.

The risk is an open-PEN fault: the PEN conductor breaks somewhere upstream. Then the earthed metalwork in your installation can rise to a dangerous voltage compared with the ground outside. For an EV outdoors, the person standing on the ground and touching the car is the person at risk. The regulations work to a touch-voltage threshold of 70V.

This is why Regulation 722.411.4.1 of BS 7671 singles out outdoor charge points. In its words as reported by the IET, PME may not be used “to supply an electric vehicle (EV) charging point located outdoors (or that might be used to charge a vehicle located outdoors)” unless one of five options is met.

The five ways the rule can be met

1. A balanced three-phase installation that also supplies other loads.
2. A very low resistance earth electrode (a TT-type arrangement).
3. A voltage monitoring device, or charger functionality, that detects PEN conductor failure.
4. A device or charger functionality for a single-phase installation.
5. An equivalent alternative device that is no less safe than options 3 or 4.

Devices in options 3 and 4 must not be capable of re-closing onto the hazard they detect. The IET published a standard for them, IET 01:2024 (open-PEN conductor detection devices, or OPDDs), on 1 October 2024, with errata in February 2026. The IET’s code of practice warns that single-phase devices should not be used for single-phase charging equipment in a three-phase installation, which matters for the few homes with a three-phase supply (see 7kW vs 22kW).

BS 7671:2018+A4:2026 was published on 15 April 2026 and the previous version is withdrawn on 15 October 2026. Sources disagree about whether Amendment 4 changed the PME exception, and the standard itself is paywalled, so we cannot confirm either way. Treat the regulation numbers on this page as the IET and NICEIC describe them.

Three solutions compared

The earth rod range is wide because no installer publishes a price list. Trade estimators disagree, with one at the lower end and another quoting more, and EV Install Pro puts earthing work with a rod in a similar span. Octopus says an earthing unit will be fitted where needed. Faithful Spark quotes earth electrodes at survey.

The rod is also not always practical. The IET notes that creating a TT system for charging equipment “may not be an appropriate solution” because of the inability to separate it from buried metalwork connected to the supply PEN conductor. Tesla’s UK manual says a dedicated earth rod is generally not practical for the Wall Connector.

Which chargers have it built in

This is from our charger data, which reads each maker’s specification. “Yes” means the maker states built-in open-PEN protection. It does not replace the upstream RCD your installer fits.

Our reviews, such as the Easee One, say the same for each model. If you are still choosing, our best home EV chargers roundup compares them.

What to ask your installer

Four questions settle most disputes. Which earthing system do I have (PME, TN-S or TT)? Does the charger have built-in open-PEN protection, and which clause does the maker cite? If you are adding a device or an electrode, why, and what does it cost? And will the test results go on the Electrical Installation Certificate? A good installer answers without hesitation. If an installer insists on an earth rod without mentioning built-in protection, get a second quote.

Earthing and bonding are real safety work, so leave them to a registered electrician; our how-to guide explains why. If you park on the street with a pavement channel, the council’s licence may specify open-PEN protection and sometimes an earth rod; see cross-pavement charging. For what each extra costs, see the installation cost guide.