18th edition amendment 1: The IET reverses over earth rods.

The growing demand for electric vehicle chargers and the development of new technology have forced the IET to update the 18th edition wiring regulations.

By Gordon Routledge
Monday 3rd February 2020

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Since the introduction of the 18th edition wiring regulations, the default method of installing a residential EV charge point has been to drive an earth rod. Creating a TT earth arrangement and separating the EV charger from the TN-C-S (PME) main electrical supply earth. The reason for this is to protect the charge point user from danger should the incoming supply develop a fault in the combined protective earth and neutral conductor (PEN).

Video report: Gary Hayers and Joe Robinson get to grip with the new amendment

What's the problem with earth rods?

Installing earth rods is time-consuming and potentially dangerous. Lots of residential EV chargers are installed close to the incoming electrical supply cable alongside the gas meter, above water mains and sewerage pipes. The potential to hit one or more of them with an earth rod is always a risk.

Installing earth rods is time consuming and risks puncturing buried services.

An alternative approach

The original 18th edition also allowed another way of compliance. What became known as a unicorn device. Called a unicorn as the technology didn't exist when the regulations were published. In other words, intelligent electronics which could monitor the incoming supply looking for a PEN fault and disconnecting the EV charger. However, the original reference contained within regulation 722.4.4.1 (iii) left a few grey areas. The regulation specified a voltage measurement of 70V RMS been the protective conductor and Earth. That's the earth with a capital E, the stuff we stand on. So how can you measure that without an earth electrode?

Indent (iii) closed with a note "Equivalent functionality could be included within the charging equipment."

The arrival of the unicorns.

Over the last year, several manufacturers have released chargers with PEN fault monitoring devices to exploit the closing clause of indent iii. Most of them use a voltage monitoring circuit which looks for abnormal supply voltages. This approach is covered in a new ident 722.411.4.1 (iv). Indent

The Zappi charger from Myenergi uses a more sophisticated approach, which is claimed will detect PEN faults not captured by clause (iv). We reported on this issue during the draft phase of the new amendment. The Myenergi technique is covered by the new 722.411.5.1 (v)

Charge-points from Pod Point, Andersen and Myenergi with PEN fault protection.

Does this spell the end of TT installations and earth rods?

Will this mean the end of TT earthing in EV charger installations?

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The new 722.411.4.1 amendment ends with NOTE 6

Creating a TT earthing system for charging equipment or the whole installation as an alternative to using a PME facility with one of the methods (i) to (v) above may not be an appropriate solution due to the inability to provide sufficient separation from the buried metalwork connected to the supply PEN conductor.