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PEN pal: The electrical safety of EV charging points

Author : William Darby, Carlo Gavazzi UK

04 April 2022

The electrical safety of EV charging points is critical. A common approach to providing protection against a damaged protective earth and neutral (PEN) conductor is to use earth rods. However, by installing a simple relay, it is possible to protect against a damaged PEN simply, cheaply and without the need for additional earthing, says William Darby, Managing Director of Carlo Gavazzi UK.

On 15 December 2021, the Government published an amendment to the Building Regulations and launched Approved Documents to cover the installation of infrastructure for the charging of electric vehicles, in both residential and non-residential buildings, in England.

The amendment is the latest in a line of initiatives to increase the number of electric charging points available, to support the growth in plug-in electric vehicles (EVs) on the UK's roads. As a result of introducing these regulations, the Government "expect[s] up to 145,000 charge points to be installed every year".

It is critical that all new charge points are electrically safe, which means the electrical supply must be installed in line with the IET Wiring Regulations, BS7671:2018.

The majority of EV charging is expected to take place at home. EV chargers for most residential applications are generally 7kW and operate on a low-voltage 230V single-phase supply. The regulations require EV chargers to have adequate earthing to ensure the user does not receive an electric shock.

A TN-C-S earthing arrangement is commonly used on low-voltage distribution systems in the UK. In this type of system, the neutral and earth functions are combined in one conductor – the protective earth and neutral (PEN) conductor – on the supply side of the installation. The PEN conductor is earthed in numerous positions, generally with earth electrodes – an arrangement commonly termed ‘protective multiple earthing’, or ‘PME’. However, for the installation inside of a home, the protective earth and neutral are kept separate.

Although this arrangement is generally very reliable, there can be a problem when there is a loss of neutral on the supply side and the EV charger installation is located outside of the bonded zone of a home... 

Read the full article in the April issue of DPA

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