Tag Archives: electric vehicle

The 4^th Edition of the IET Code of Practice for Electric Vehicle Charging Equipment Installation is now available. Our Managing Director, who is the lead author of the publication, provides a commentary on the key changes and new information.

The 4^th Edition, available from the IET, is updated to BS 7671:2018 + A1:2020, and also includes:

• guidance for on street installations updated to cover a wide range of situations
• new information on load unbalance in three-phase installations
• guidance on the selection and use of new open-PEN detection
• guidance on the dangers associated with TT islands, and safe separation distances below ground for earth electrodes
• Amendment 1 (2020) to BS 7671:2018 in its entirety

Open PEN detection where PME conditions apply

Regulation 722.411.4.1 (iii), (iv) and (v) permit the use of protective devices which detect open-circuit protective earth and neutral (PEN) conductors in the PME supply.

These devices are relatively new, and there are no product-specific standards available at present. The 4^th Edition provides the guidance that installers need to select and install these new protective devices.

The device described in 722.411.4.1 (iv) is only suitable for installations with single-phase supplies, and should not be used for single-phase charging equipment in a three-phase installation. An important feature of the wording in 722.411.4.1 (iii) and (iv) is that the devices shall not be capable of re-closing onto the conditions they detect are hazardous. In order to provide equivalent safety, a device described in 722.411.4.1 (v) must also have the same feature.

A new approach to phase unbalance in three-phase systems

Our Managing Director has developed a new approach to determining whether exception (i) to Regulation722.411.4.1 applies in a three-phase system. This method removes the need for calculations using the formulas in Annex 722, A722.1 and A722.2, and relies only on knowledge of the worst-case unbalance conditions, and either use of a lookup table, or application of a rule-of-thumb.

This method is described fully in Annex J of the IET Code of Practice for EV Charging Equipment Installation 4^th Edition.

Updated guidance on deriving a TT earthing arrangement from a TN supply

Unsafe installation practices have been observed where a separate TT supply is used for electric vehicle charging equipment. Further, this approach may not offer any benefit at all in small curtilage properties, such as a common semi-detached dwelling.

New and extended guidance is now included, to help designers and installers:

• determine when it is unsafe to employ a TT earthing arrangement in installations with TN supply earthing arrangements
• understand the risks associated with driving electrodes
• ensure adequate separation distances below ground, between exposed-conductive-parts connected to different earthing arrangements
• ensure an adequate separation distance below ground between the TT earth electrode, and buried conductive parts connected to the TN earthing arrangement, and understand that in certain cases, distribution network operators require a greater separation distance

Other new or revised guidance

There is an update to the section on Vehicle as storage, including new material by Dr Andrew Crossland and Mark Collins of Advance Further Energy, and new arrangements for installation of EVSE in prosuming installations by our Managing Director. The section on Integration and smart infrastructure has also been updated to include new material from Cameron Steel of Silver EMS.

The DNO notification process has been updated, and guidance is now included on earthing arrangements for the installation of Mode 4 (DC rapid charging) EVSE, some of which employs isolation between the AC source and the DC vehicle charging supply.

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