EV Chargers and the Importance of Open PEN Fault Protection

With the rapid uptake of electric vehicles across the UK, domestic EV charge points have become a standard addition to many properties. However, unlike most household loads, an EV charger introduces a direct conductive connection between the electrical installation and a vehicle chassis parked outdoors.

That changes the risk profile significantly.

One of the most critical safety considerations in UK installations is Open PEN fault protection — particularly on TN-C-S (PME) earthing systems.

This article explains:

• What an Open PEN fault is • Why it is dangerous • What BS 7671:2024 requires • The protection methods available • What electricians and property owners should understand

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1. What Is a PEN Conductor?

In a typical UK TN-C-S (PME) supply provided by the DNO, the Protective Earth (PE) and Neutral (N) functions are combined in a single conductor in the supply network. This is known as the PEN conductor (Protective Earth and Neutral).

If that conductor becomes open circuit upstream of the installation, it is referred to as an Open PEN fault.

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1. What Happens During an Open PEN Fault?

If the PEN conductor is lost:

• The installation loses its earth reference • The neutral can float • Exposed-conductive-parts can rise toward line voltage

In a typical domestic setting, bonding and parallel paths often limit the rise in potential.

However, with an EV charger:

• The vehicle chassis is connected to CPC • The vehicle is in contact with the ground (via tyres, damp ground, or a person standing on earth) • The charging cable creates a path outside the equipotential zone

This can result in the vehicle body reaching a dangerous touch voltage relative to true earth.

Under certain load imbalance conditions, this could approach 230V to earth — posing a serious electric shock risk.

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1. Why EV Chargers Are Different

EV charge points are typically:

• Installed externally • Connected to PME earthing systems • Used by members of the public • Providing simultaneous contact between installation earth and true earth

BS 7671:2024 (Section 722) recognises this elevated risk and mandates specific protection measures where PME is used.

This is not optional.

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1. What Does BS 7671:2024 Require?

Section 722 of BS 7671:2024 requires that where a TN-C-S system is used to supply EV charging equipment outdoors, provision must be made to protect against dangers arising from an Open PEN conductor.

There are 3 main compliant approaches:

1. Built-in Open PEN Fault Detection (Most Common)

Modern chargers such as:

• Rolec • Easee • Pod Point

often incorporate internal voltage monitoring that:

• Detects abnormal line-to-earth voltage • Detects neutral displacement • Automatically disconnects all live conductors

This is the most common method in domestic installs.

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1. Installation of a Separate Earth Electrode

A TT arrangement can be created for the charger by:

• Installing an earth electrode • Separating the charger earth from PME • Ensuring adequate disconnection times

However, this introduces:

• Additional design considerations • Earth resistance testing requirements • Potential nuisance tripping if not designed properly

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1. Use of a Device Providing Automatic Disconnection on PEN Failure

External PEN fault protection devices are also available, though less common in domestic settings where built-in protection is present.

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1. What Happens If It Is Not Installed?

Without compliant Open PEN protection:

• The installation is non-compliant with BS 7671:2024 • Certification cannot be issued correctly • There is genuine shock risk • Insurance implications may arise • DNO requirements may be breached

For landlords, this also creates potential EICR issues and liability exposure.

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1. How Does an Open PEN Device Actually Detect the Fault?

Most modern units monitor:

• Voltage between Line and Earth • Voltage between Neutral and Earth • Line voltage imbalance

If the device detects that:

• Line-to-earth voltage exceeds safe thresholds • Neutral is no longer stable • Voltage rises beyond preset parameters

It disconnects both Line and Neutral within milliseconds.

This removes the dangerous potential difference before someone can make contact.

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1. Key Installation Considerations for Electricians

When installing an EV charger, electricians should ensure:

• Supply earthing arrangement is correctly identified • Main bonding is verified and compliant • Ze values are appropriate • Charger incorporates compliant PEN fault protection or suitable alternative • RCD type is correct (typically Type A with 6mA DC detection or equivalent) • Certification is completed correctly

Failure in any of these areas results in a non-compliant installation.

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1. The Bigger Picture

As EV adoption grows, the grid is evolving — but PME earthing remains common in the UK.

Open PEN fault protection is not an “extra” feature.

It is a critical life safety mechanism.

When installed correctly, EV chargers are extremely safe. When installed incorrectly, they can introduce a unique and serious hazard.

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Final Thoughts

For homeowners, landlords and businesses:

If you are installing an EV charger, ensure the installer can clearly explain:

• The earthing system • The Open PEN protection method used • How compliance with BS 7671:2024 is achieved

For electricians:

Section 722 is not an area to cut corners. Understanding the mechanism of PEN failure and the protective measures available is now fundamental competence in modern domestic installations.

Frequently Asked Questions (North East UK)

What are my legal electrical responsibilities as a Landlord in Newcastle? As a landlord in the North East, you are legally required to ensure that all electrical installations in your rental property are safe when tenants move in and are maintained in a safe condition throughout the duration of the tenancy. This includes obtaining a satisfactory Electrical Installation Condition Report (EICR) every 5 years or at the start of a new tenancy. Switch Electrical & Mechanical Services provides comprehensive EICR audits for landlords across Newcastle, Sunderland, and Gateshead.

How much does an EICR cost for a standard property in the North East? The cost of an EICR depends on the size of the property and the number of circuits. Switch Electrical & Mechanical Services provides highly competitive, transparent pricing for landlords in the North East. We also offer discounted rates for landlords with multiple properties or HMOs requiring block certification.

What happens if my rental property fails an EICR? If an EICR identifies 'C1' (Danger Present) or 'C2' (Potentially Dangerous) codes, the installation is deemed 'Unsatisfactory'. Landlords have exactly 28 days to complete the necessary remedial work. Our team at Switch Electrical & Mechanical Services can provide immediate, fixed-price quotes for all remedial work following an inspection to ensure you remain legally compliant.