A PEN fault detection device is one way to deal with an open-PEN risk on a PME (TN-C-S) supply when you install an outdoor EV charger. It is not a brand of charger and it is not optional decoration. If the combined neutral and earth in the street is lost, metalwork on the car and the charger can rise to a dangerous voltage. UK practice is to design that out, often with a device built into the charger or a separate protective arrangement, or by using a different earthing method where that is the right design.
Check pEN fault detection on a home EV charger before you accept a price
Ask for the earthing type in writing after the survey. If the supply is TT already, the design is different and a rod and RCD arrangement may be the story instead of a PEN device. Do not buy the device yourself from a marketplace and expect any installer to warranty the mix.
The price effect of pEN fault detection on a home EV charger
Open-PEN protection is part of a compliant install, so it should sit inside the headline price when the charger includes it. If the quote adds a separate device, earth electrode or conversion, that line needs a reason. It is not a surprise extra to discover on the day.
A miss that shows up later: pEN fault detection on a home EV charger
The mistake is assuming every charger sold online is legal to connect outdoors in the UK, or that bonding the water pipe is a substitute for the correct protective measure. Bonding and open-PEN protection answer different faults.
Write pEN fault detection on a home EV charger into the quote
The quote and the certificate should state the earthing arrangement and how open-PEN risk is dealt with. If those words are missing, ask before you pay a deposit.
PEN fault detection on a home EV charger
Most modern UK homes are PME. The installer has to know the earthing system at your cut-out, not guess from the age of the kitchen. Many current wallboxes include open-PEN protection. Older or imported units may not, which is one reason a cheap online charger becomes expensive once a competent person refuses to connect it.
- Confirm PME, TN-S or TT from the survey, not from a neighbour
- Prefer a charger the installer will warranty with its protective device
- Do not treat a caravan hook-up lead as equivalent protection
- Ask which device or method is used if the unit does not include it
Frequently asked questions
Does every home need a PEN fault device?
No. It depends on the earthing system and the design. PME outdoor charging is the common case where open-PEN protection is discussed. TT supplies are designed differently.
Can I add one later?
Sometimes, but it is better chosen with the charger. A later retrofit can mean changing the unit or the board.
Is this the same as an RCD?
No. An RCD detects some leakage and shock faults. Open-PEN protection addresses a lost combined neutral and earth on PME. You can need both functions in the design.
Will a grant form ask about it?
Competent installs follow the wiring rules whether or not a grant is involved. The certificate is the evidence, not a forum post.
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How this guide was prepared
This guide was written by the Local EV Installers Editorial Team. We compare official guidance, legislation and established consumer information, separate general information from project-specific advice, and show publication dates and sources. We do not accept installer accreditation claims at face value.