Opinion: Why BS7671 amendment 1 is potentially dangerous

Could a potentially dangerous situation be lurking in the detail of the proposed changes to the 18th edition wiring regulations?

by Gordon Routledge
Thursday 24th October 2019

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*** UPDATE: - The 18th edition wiring regulations have now been updated with amendment 1 - see this article for the latest information. ***

IP66 testing — Electric Vehicles - BS 7671:2018 Amendment 1 - Public draft

In September the IET announced a fast track amendment to the latest wiring regulations. The aim is for the changes to hit the street in January 2020. Hitting the street is the issue behind the need to make some changes. Or rather, the growing demand for electric vehicle (EV) chargers appearing on driveways across the UK.

So what's the problem?

It's all to do with earth rods and PME (TNCS) supplies. Under the current, non-amended version of BS7671, you can't realistically install an EV charger to a PME supply. The way around this, in most residential projects, has been to fit an earth rod. The EV charger becomes a TT installation separated from PME supply.

However, earth rods are messy and can be tricky to install. Note for electricians. Check your liability insurance to see if you're covered for installations more than one-meter depth. Driving an earth rod into the ground creates a risk of hitting other services. So moving away from earth rods could be a wise move.

Buried away in section 722 of the current 18th edition was a clause which enabled installation directly to PME supplies.

722.4.4.1 (iii) - within the current 18th edition

"Protection against electric shock is provided by a device which disconnects the charging point from the live conductors of the supply and protective earth in accordance with Regulation 543.3.3.101(ii) within 5s in the event if the voltage between the circuit protective conductor and Earth exceeding 70v rms. The device shall not operate if the voltage exceeds 70v rms for less than 4 s. The device shall provide isolation. Closing or resetting of the device shall be by manual means only. Equivalent functionality could be included within the charging equipment."

We reported back in April that several manufacturers of EV chargers had introduced chargers to utilise clause (iii). Since then, there has been a lot of debate as to whether these devices work.

We reviewed the Zappi 2 charger from Myenergi in September and found the secret of how it works. The Zappi 2 identifies all potential PEN conductor failure modes.

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What changes with amendment 1

Indent (iii) as above has been modified to apply just to three-phase installations. The amended version introduces a new indent (iv) for single-phase installations.

722.4.4.1 (iv) - new indent proposed for amendment 1

"Protection against electric shock in a single-phase installation is provided by a device, or means of functionality included within the charging equipment, which electrically disconnects the vehicle from the charging point within 5 s in the event of the utilisation voltage at the charging point, between the line and neutral conductors, being greater than 253V rms or less than 207V rms."

In other words, it is identifying a PEN conductor fault by monitoring the supply voltage between live and neutral conductors. While this may sound a credible solution, it may not work in all types of PEN fault condition.