Summary:
PME protection is one of the most important — and misunderstood — parts of an EV charger installation. This post explains what PME is, why it matters under BS 7671, and how to meet regulations safely with the right standalone devices and pre-built solutions.
What Is PME Protection?
PME (Protective Multiple Earthing) is a type of earthing arrangement widely used in the UK’s TN-C-S systems. In most homes and small businesses, the neutral and earth conductors are combined within the supply cable and then separated at the property.
While PME is safe under normal conditions, it becomes dangerous if the supply neutral is lost — known as a PEN fault. When this happens, exposed metal parts (like a car chassis connected to an EV charger) can rise to mains voltage, creating a serious electric shock risk.
That’s where PME protection comes in.
Why EV Chargers Need PME Protection
Regulation 722.411.4.1 of BS 7671 (18th Edition + A2:2022) requires EV charge points to disconnect automatically in the event of a PEN fault — unless an alternative earthing arrangement (like TT) is used.
EV chargers with built-in PEN fault detection are becoming more common, but many units — including several Tesla Wall Connector versions — don’t include it. Installers therefore need an external PME protection device to remain compliant and safe.
How PME Protection Works
A PEN fault detection unit continuously monitors the voltage between line, neutral, and earth conductors.
If the voltage strays outside safe limits (typically ± 10 % of nominal), it instantly disconnects the EV charger from the supply.
Modern PME devices — like the WCED 3-Phase PEN Fault Detection & Surge Protection Unit — combine several safety features in one enclosure:
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✅ PEN Fault Detection (400 V 3-Phase)
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✅ Type 2 Surge Protection (SPD)
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✅ RCBO Overcurrent Protection
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✅ Optional Main Isolator
This saves space and simplifies wiring, especially in three-phase commercial installs or Tesla multi-charger setups.
Choosing the Right PME Protection Device
When selecting PME protection, consider:
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Charger Compatibility – Tesla, Zappi, Hypervolt, and others have different earthing needs.
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Single vs Three Phase – Match your protection device to the supply.
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RCBO or MCB – For added fault and overload protection, choose RCBO.
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Surge Protection – Required under BS 7671 A2:2022 unless risk assessed otherwise.
At Eco Harmony, we stock several ready-to-install options:
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3-Phase PME 40 A RCBO + Surge Protection — ideal for Tesla Wall Connector installs.
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PEN Fault Detection with Surge Protection — compact and compliant.
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3-Phase PME MCB Standalone Unit — for when your charger already includes RCBO protection.
Installation Tips for Electricians
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Always verify supply type before connecting any EV charger.
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Test PEN detection function after installation using manufacturer guidance.
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Mount units in a dry, accessible location (IP 40 + for indoor, IP 65 + for outdoor).
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Ensure surge protection modules are replaceable and labelled.
If you’re wiring multiple chargers, consider using a TPN Distribution Board + SPD — you’ll even get 25 % off MCBs when bought together.
Real-World Example
A recent installer in Manchester fitted a Tesla Gen 3 Wall Connector on a three-phase supply. The charger had DC leakage detection but no PME protection, so they used the Eco Harmony 3-Phase PME RCBO + SPD Unit.
Result? The install passed inspection without issue, the homeowner’s insurance was satisfied, and the charger’s operation remained uninterrupted — all for less wiring time.
Conclusion
PEN and PME faults may be rare, but compliance and safety aren’t optional. By fitting a dedicated PME protection device with surge protection and RCBO in one enclosure, you can future-proof your installations, protect your clients, and avoid callbacks.
Eco Harmony supplies trusted UK-made WCED protection products that help installers stay safe, compliant, and efficient — without overspending.
👉 Explore PME Protection Solutions: https://ecoharmony.co.uk/collections/surge-protection-pme