What are the earthing arrangements for electric vehicle charging points?

The top electric cars and new EV models on the market support ever-faster charging, which means higher-power charge points. Even domestic EV chargers offer up to 22kW if you have a three-phase electricity supply.

Look underneath an electric vehicle, and you will notice that the high-voltage components are hidden away, usually behind bright orange safety covers with clear warning notices. But what about the charging points?

Electrical safety is an obvious consideration when installing a home charging point, and this is governed by several regulations from the Institution of Engineering and Technology (IET), including:

• The IET Code of Practice for Electric Vehicle Charging Equipment Installation
• The IET Wiring Regulations Requirements for Electrical Installations

So what are the options when earthing electric vehicle charging points – and do you need to earth an EV charging point at all?

Earth Rods For EV Charge Points

Earth rods are fast and cost-effective. They consist of a conductor (e.g., a metal rod) driven down into the ground — literally an electrical connection into the ‘earth’.

They are a way to comply with the IET Wiring Regulation 722.411.4.1, which aims to prevent electric shock hazards from arising in the event of a fault with the domestic electricity supply’s own TNCS earthing system.

What Does Tncs Stand For?

TNCS (PME) is the earthing system used in most domestic electricity supplies in the UK. It stands for:

• Terra (‘Earth’ in Latin)
• Network (meaning the earth connection is via the supply network)
• Combined (neutral and earth cables are combined in the supply cable)
• Separate (neutral and earth cables are separate from the electric meter onwards)

PME (Protective Multiple Earthing) is an alternative common name for this arrangement.

In the event of a failure in this earthing system, EV domestic charging points must have an alternative way to prevent a potentially fatal (or damaging to equipment) electric shock.

Pros And Cons Of Ev Charge Point Earth Rods

As mentioned, earth rods are fast, easy, and cost-effective to install alongside a standard domestic EV charge point. However, they are not a perfect solution, as outlined below.

Some of the objections to earthing rods for domestic charge points include the following:

• Visual impact of the rod or conduit running from the charge point into the ground
• Risk of impacting buried utilities, including gas, water, and other electricals
• Proximity risks due to multiple earth rods buried too close together

In the worst-case scenario, the current discharged from an earth rod could re-emerge via nearby metal objects if they are too close to each other underground, creating a new risk of electric shock or material damage to buildings, vehicles, and possessions.

Alternatives To Charge Point Earth Rods

Increasingly, domestic EV charging points are being designed to comply with the regulations but do not need an earth rod to run from the charger into the ground. So how is this possible?

The answer lies in sophisticated electronics, similar to the systems that shut off an EV charger once the battery reaches 100% to avoid over-charging it.

In this case, similar control systems monitor the mains power supply for indications of an electrical fault or a failure in the supply’s TNCS (PME) earthing arrangement.

What If There’s A Fault?

No-earth charging systems have been around since at least 2017. In the event of a fault on either the earth or neutral wire in the mains supply, the charger disconnects from the vehicle automatically.

IET Wiring Regulation 722.411.4.1 was amended in 2020 to allow several ways to protect against a supply fault, including using devices that disconnect the live and earth connections in under five seconds in response to certain fault conditions.