3 February 2020 heralded the publication of the first amendment to BS 7671:2018 Requirements for electrical installations (IET Wiring Regulations 18th Edition). Graham Kenyon discusses an important aspect of this update.
The changes will support the rollout of electric vehicle charging equipment infrastructure.
Use of a PME earthing terminal
The principal change introduced in Amendment 1 relates to Regulation 722.411.4.1. This makes it possible to use the emerging technology of open-PEN detection devices, which were not available when BS 7671:2018 was published. This change should be well-received in the industry, as it is not always practicable, or safe, to derive a TT earthing arrangement, where other parts of the installation have a different earthing system such as TN-C-S (PME) or TN-S.
The PME earthing terminal may be used for installations with a single-phase supply (to the whole installation) where:
- An additional earth electrode is provided that meets the requirements of 722.411.4.1 (ii). It may be impractical to achieve a low enough earth electrode resistance in many single-phase installations.
- A single-phase open-PEN detection device is used, that complies with 722.411.4.1 (iii), (iv) or (v). A device complying with (iii) will require a measurement earth electrode in single-phase installations. A device to (iii) or its equivalent in (v) may be installed in or near the charging equipment, or upstream of the charging equipment. A device to (iv) or its equivalent to (v) is intended to be installed in or near the charging equipment.
The PME earthing terminal may be used for installations with three-phase supplies (to the whole installation) where:
- The three-phase installation is sufficiently well balanced so that it is unlikely that the touch voltage will exceed 70 V rms if the PME supply neutral breaks, according to 722.411.4.1 (i).
- An additional earth electrode is provided that meets the requirements of 722.411.4.1 (ii). Depending on the anticipated worst-case phase unbalance, it may be possible to achieve a low enough earth electrode resistance in three-phase installations.
- An open-PEN detection device is used, that complies with 722.411.4.1 (iii) or (v). The device may be installed in or near the charging equipment, or upstream of the charging equipment. If the device is upstream in a three-phase portion of the network, it may protect single-phase charging equipment downstream. Where a device to (iii) requires an earth electrode, it may be installed on single-phase circuits or in/near single-phase charging equipment.
The relevant distribution network operator (DNO) should be consulted regarding the use of open-PEN detection devices for on-street installations. Street lighting supplies are often effected through three-phase distribution mains and therefore would typically be classed as three-phase supplies for the purposes of Regulation 722.411.4.1.
What is the problem with deriving a TT earthing system for the charging equipment as an alternative for PME supplies?
The problems with deriving a TT earthing system from a PME supply in a particular installation may include:
- Ensuring sufficient separation below ground from buried metalwork connected to the PME earthing system. If too little separation is provided, the vehicle is, for all practical purposes, connected to the PME earthing system.
- Simultaneous contact assessments are required, between the charging equipment/vehicles and extraneous-conductive-parts and exposed-conductive-parts connected to the original installation earthing system.
- The possibility of returning a touch voltage in PME broken neutral situations, for someone standing next to the vehicle on charge, if they are standing above buried metalwork or extraneous-conductive-parts connected to the PME earthing system. This may be just as hazardous as the original PME risk, under certain ground/soil conditions.
- The possibility of striking buried services if driving rods or excavating to install earth electrodes.
The above situations are more likely to be found in small curtilage properties, such as many dwellings.
Further guidance – 4th Edition of the IET Code of practice for EV charging equipment installation
The 4th Edition of the IET Code of practice for EV charging equipment installation is due to be published very soon. This is a major update with extensive guidance on Amendment 1:2020, and the topics discussed in the article.
Improvements include information on:
- Use of open-PEN detection devices.
- Issues with TT systems, including recommended separation distances underground.
- Improved risk assessment forms.
- Phase unbalance in three-phase systems, including a table and rule-of-thumb which can be used to avoid complex calculations.
In this interview following the London electric vehicle charging infrastructure strategy launch, at the IET, Savoy Place, London, on Monday 17 June 2019, Graham discusses the challenges that, particularly in UK cities, must be overcome to realise our climate change and pollution commitments.
Our Managing Director, Graham Kenyon, was pleased to support London Mayor Sadiq Khan’s launch of the plan for the electric vehicle charging infrastructure in London on Monday 17 June 2019.
Graham, Chair of the IET’s Wiring Regulations Policy Committee, author of the 3rd Edition of the IET’s Code of practice for electric vehicle charging equipment installation, chaired a technical question and answer session as part of the launch event.
Read more about the launch in this IET Member News article.
G Kenyon Technology Ltd, as a content partner with the IET Academy, has developed an on-line course for designers and installers of Electric Vehicle Charging Equipment Installations.
Learn on-line, at your own pace
This course will cover: the design of electrical installations for, and specification of, electric vehicle charging equipment installations; the requirements detailed in Section 722 of BS 7671:2018; and recommendations of the IET Code of Practice for Electric Vehicle Charging Installations, 3rd Edition. It provides an understanding of the key requirements for protection against electric shock, including selection and use of earthing systems, and introduces vehicle-as-storage, wireless power transfer (WPT) and smart infrastructure installations.
Many electrical installations now incorporate new technologies, including embedded generation and home or building automation systems. As use of these technologies becomes more widespread, we need to be ever mindful that control of power to a circuit no longer relies on simple human switching operations. Electrical energy storage technologies that are capable of operating in island mode, continue to provide power when the grid is isolated.
Some incidents that have occurred recently when implementing energy storage systems outside the UK prompted Dr Andrew Crossland and myself to write an article for IET’s Wiring Matters. The article highlights the risks, and discusses safe isolation.
Further guidance on electrical energy storage systems can be found in the IET Code of Practice for Electrical Energy Storage Systems.
Note: G Kenyon Technology Ltd cannot be held responsible for the contents of other web-sites linked from this post.
IET publishes Corrigendum for the 18th Edition
The IET have today (20 December 2018) published a Corridengum to BS 7671:2018 (IET Wiring Regulations 18th Edition).
To download the Corrigendum, please visit the IET’s dedicated BS 7671 web page.
G Kenyon Technology Ltd are not responsible for the contents of web-sites linked from this post
7 January 2018 Principal Speaking at Seminar BS 7671:2018 18th Edition of the IET Wiring Regulations Interpreted by the experts
Hear about key changes being introduced in 18th Edition, from key committee experts.
BS 7671:2018 Requirements for Electrical Installations should be used for new designs from 1 January 2019. If you’ve been wondering what has changed and what you might need to do differently, attending this update seminar just four days later will give you the answers.
The three experts have active roles in the JPEL/64 committee led approach to the IET Wiring Regulations, so are well-placed to interpret the new edition and explain how it impacts the way you work.
Benefit from the discussion encouraged throughout the day, with plenty of time for delegates to question what, why and how with our panel as well as other delegates. You won’t get such comprehensive clarification by reading articles or sifting through the Regs themselves.
7 January 2019 IET London: Savoy Place
John Bradley, Chair, JPEL/64 – Electrical Installations
Mark Coles, Head of Technical Regulations, IET and Secretary, JPEL/64 Sub-Committee D – External Influences
Graham Kenyon, Chair IET WRPC, Chair JPEL/64 Sub-Committee D – External Influences
1. The content of this post was provided as an IET mailshot in March 2018.
2. G Kenyon Technology Ltd cannot be held responsible for the content of external web-sites linked from this post.
Our Principal, Graham Kenyon, will be speaking at the IHEEM Electrical Seminar being held on the 19th September 2018 at the Thackray Medical Museum in Leeds.
For further information see, the IHEEM web-site.
NOTE: G Kenyon Technology Ltd cannot be held responsible for the contents of other web-sites linked from this post.
Graham’s article in the latest IET Wiring Matters explores earth fault loop impedance values for supplies up to 100 A, following the update of ENA Engineering Recommendation P23 in 2018.
The article can be viewed here.
G Kenyon Technology Ltd are not responsible for the contents of other web-sites linked from this page.
The suite of Guidance Notes to support the recently published BS 7671:2018 Requirements for electrical installations (IET Wiring Regulations 18th Edition) is now available to order from the IET on their web-site. Guidance Note 3 is already available, along with the On-Site Guide.
Included in this, are the following publications, for which our Managing Director and Principal Consultant, Graham Kenyon, is proud to be the author of the amendments in the latest Editions.
Order your copies now.
IET Guidance Note 5: Protection Against Electric Shock, 8th Edition
IET Guidance Note 6: Protection Against Overcurrent, 8th Edition
IET Electrical Installation Design Guide, 4th Edition
IET Code of Practice for Electric Vehicle Charging Installations, 3rd Edition
Graham is also an acknowledged contributor for the following Guidance Notes:
- Guidance Note 1: Selection and Erection, available September 2018
- Guidance Note 3: Inspection and Testing, available August 2018
- Guidance Note 8: Earthing and Bonding, available November 2018