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Wiring Matters – Issue 81 – July 2020

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Wiring Matters – Issue 81 – July 2020

Here is what you will find in the July 2020 (Issue 81) of the IET Wiring Matters magazine.

History of insulation resistance testing

There has been a lot of activity on the IET Engineering Communities forum recently regarding the background of the 1 megohm minimum value for insulation resistance. Let’s take a look at how this value was arrived at in BS 7671:2018+A1:2020.

Draft for Public Comment: IET Code of Practice for Electrical Energy Storage Systems, 2nd Edition

The IET are happy to announce that the Draft for Public Comment for IET Code of Practice for Electrical Energy Storage Systems 2nd Edition is now live.

This Code of Practice looks at Electrical Energy Storage System (EESS) applications and provides information for practitioners to safely and effectively specify, design, install, commission, operate and maintain a system. This 2nd Edition has been updated to take account of developments in the industry, and progress in standardisation.

The all-new 5th Edition of the IET Code of Practice for In-Service Inspection and Testing of Electrical Equipment

In this article, James Eade, author of the 5th Edition, gives a brief insight into the changes to this important Code, due for publication later this year.

Amps per Pound

The idea of sizing a cable to reduce energy loss in distribution is nothing new and has been considered for many years, but with competitive tendering for work and the continual search for cost reductions (also known as ‘value engineering’), the modern design of an electrical installation tries to reduce the materials utilised to a minimum.

Asbestos guidance for electricians

Asbestos was widely used in building construction, both as a building material and for its useful insulation and fire protection properties, for many years during the 20th century.

Its use was progressively reduced between the 1970s and 1999 when all remaining forms were finally prohibited in the UK with the implementation of the Asbestos (Prohibitions) (Amendment) Regulations 1999. Asbestos has also been removed from various properties over the years for various reasons, for example, because of damaged material, or for refurbishment and demolition, but a substantial proportion of the original products still remain. These materials, if undetected, can present an ongoing risk to workers carrying out building repair and maintenance or improvement and refurbishment work. Workers at potential risk include electricians and other building trades. 

Amendment number 1 to BS 7671:2018+A1

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Amendment 1 of BS 7671:2018 was published at the beginning of February this year and may be implemented immediately. The amendment concerns Section 722 of BS 7671:2018 (electric vehicle charging installations). In this article, we give a brief overview of some of the main changes to Section 722.

Protection against electric shock

Regulation 722.411.4.1 concerning the use of protective multiple earthing (PME) supply has been redrafted. Indent (iii) has been fully revised. In addition, Regulation 722.411.4.1 now includes an additional indent (iv) to cover single-phase installations and a further additional indent (v) has been added. Regulation 722.411.4.1 does not allow PME to be used to supply an electric vehicle (EV) charging point located outdoors (or that might be used to charge a vehicle located outdoors) unless you meet (i) or (ii) or (iii) or (iv) or (v) of 722.411.4.1.

A summary of the requirements of the indents to Regulation 722.411.4.1 is as follows.

Regulation 722.411.4.1(i) refers to a situation where a connecting point is supplied from a three-phase installation used to supply loads other than charging points and where the load is sufficiently well balanced.

Regulation 722.411.4.1(ii) requires a very low resistance earth electrode to mitigate the effects of an open-circuit (PEN) conductor fault on the supply.

Regulation 722.411.4.1 (iii) has been revised and refers to a voltage monitoring device (or functionality within the charging equipment) that detects PEN conductor failure. The informative Annex to Section 722 describes that suitable arrangements include measurement of the voltage between either:

   a. the circuit protective conductor (CPC) and a suitable measurement earth electrode, or
   b. the CPC and a reference point derived from the line conductors of a three-phase system provided that suitable precautions are also taken to disconnect the device when the supply to one or more of the line conductors is interrupted.

Regulation 722.411.4.1 now includes an additional new indent (iv) to cover protection by a device (or functionality within the charging equipment) for a single-phase installation.

Finally, Regulation 722.411.4.1 includes an additional new indent (v), which allows protection against electric shock to be provided by the use of an alternative device to those in (iii) or (iv), providing that it does not result in a lesser degree of safety than using (iii) or (iv). The indent states that equivalent means of functionality could be included within the charging equipment.

The touch voltage threshold of 70 V mentioned in Regulation 722.411.4.1 is on the basis that Table 2c (ventricular fibrillation for alternating current 50/60 Hz) of IEC 60479-5{ed1.0} gives a value of 71 V for both-hands-to-feet, in water-wet conditions with medium contact area (12.5 cm2).

Regulation 722.411.4.1 includes some important notes. Note 5 explains that BS 7671 does not deal with the safety requirements for the construction of electrical equipment. Where equipment to be used is not covered by a British or Harmonized Standard, the electrical installation designer should establish that the manufacturer of the equipment has ensured that the equipment satisfies the safety objectives of the relevant directive(s).

Note 6 states that creating a TT earthing system for charging equipment or for the whole installation, as an alternative to using a PME earthing facility with one of methods (i) to (v) above, may not be an appropriate solution, due to the inability to provide sufficient separation from buried metalwork connected to the supply PEN conductor.

What is protective multiple earthing (PME)?

The Electricity Safety, Quality and Continuity Regulations 2002 (ESQCR) (as amended) permit the distributor to combine neutral and protective functions in a single conductor, provided that (in addition to the neutral to Earth connection at the supply transformer) there are one or more other connections with Earth. The supply neutral may then be used to connect the CPCs of the customer’s installation with Earth if the customer’s installation meets the requirements of BS 7671.

PME has been almost universally adopted by distributors in the UK as an effective and reliable method of providing their customers with an earth connection. Such a supply system is described in BS 7671 as TN-C-S. However, whilst a PME terminal provides an effective and reliable facility for the majority of installations, under certain supply system fault conditions (external to the installation), a potential can develop between the conductive parts connected to the PME earth terminal and the general mass of Earth.

The potential difference between true Earth and the PME earth terminal is of importance when:

   a. body contact resistance is low (little clothing, damp/wet conditions), and/or
   b. there is relatively good contact with true Earth. 

Contact with Earth is always possible outside a building and, if exposed-conductive-parts and/or extraneous-conductive-parts connected to the PME earth terminal are accessible outside the building, people may be subjected to a voltage difference appearing between these parts and Earth.

Residual current device (RCD) protection

The requirements for RCD protection have been redrafted. The Regulation now contains further requirements for Type B and Type A or Type F RCDs, to take account of DC fault current, as follows (extract below):

“Except where provided by the EV charging equipment, protection against DC fault currents shall be provided by:

(i) an RCD Type B, or

(ii) an RCD Type A or Type F in conjunction with a residual direct current detecting device (RDC-DD) complying with BS IEC 62955 as appropriate to the nature of the residual and superimposed currents and recommendation of the manufacturer of the charging equipment.”

ANNEX A722 (Informative)

Annex A722 has been redrafted. This Annex now includes guidance on the voltage monitoring device described in Regulation 722.411.4.1 (iii). In addition, the Annex now includes an example arrangement of a separated system as described in Regulation 722.413. 

Conclusion

It is important to note that this article gives only a very brief overview of some of the changes in the Amendment to BS 7671:2018. For more information, please refer to BS 7671:2018, Amendment 1:2020.

By: Geoff Cronshaw – IET Wiring Matters – Issue 79

Wiring Matters – Issue 79 – March 2020

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Issue 79 (March 2020) of Wiring Matters includes articles on Amendment 1 to BS 7671, the private rented sector, the Electrotechnical Assessment Specification and the return of our Mythbusters column.

Amendment number 1 to BS 7671:2018+A1

Amendment 1 of BS 7671:2018 was published at the beginning of February this year and may be implemented immediately. The amendment concerns Section 722 of BS 7671:2018 (electric vehicle charging installations). In this article, we give a brief overview of some of the main changes to Section 722.

The Electrotechnical Assessment Specification – January 2020 Edition

The Electrotechnical Assessment Specification (EAS) Committee is made up of a wide range of experts who are passionate about the electrotechnical industry. It includes representatives from the competent person scheme providers, certification and registration bodies, industry trade associations, the Ministry of Housing, Communities and Local Government, the Health and Safety Executive, Electrical Safety First and the IET (which also provides administrative support to the committee).

Mythbuster #5 – Will any old terminal block do?

In this issue, James Eade investigates terminals and connectors.

The Electrical Safety Standards in the Private Rented Sector (England) Regulations 2020

Between 17 February and 16 April 2018, the government invited comments on the Electrical Safety Standards Working Group’s decision to make a recommendation to introduce mandatory inspection and testing for private rented properties.

Getting important labelling right leaves a lasting impression

What you leave behind after an installation speaks volumes. While electrical labelling is most importantly about safety, it should also be convenient, professional, time-saving, making your life easier and leave a lasting impression with your customers.

You can read the full story’s here

Millions more UK homes to be powered by renewables

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Details of the next round of the Contracts for Difference scheme, which opens in 2021, have been set out today, Monday 2 March.

This latest round will be open to renewable technologies including onshore wind and solar, with proposals to include floating offshore wind. The scheme will also be changed to facilitate the deployment of energy storage.

Local communities will have a more effective voice on developments that impact them, through proposals for tough new guidance on community engagement for developers of onshore wind across Great Britain, also announced today. They will have a definitive say on whether projects are allowed to proceed. It will remain the case that no English onshore wind project can proceed without the consent of the local community.

The Committee on Climate Change have said that we need to quadruple renewable energy generation in the UK to reach net zero by 2050, and today’s announcement is a step in that direction.

Secretary of State for Business and Energy Alok Sharma said:

Ending our contribution to climate change means making the UK a world leader in renewable energy.

We are determined to do that in a way that works for everyone, listening to local communities and giving them an effective voice in decisions that affect them.

RenewableUK’s Chief Executive Hugh McNeal said:

The government is pressing ahead with action to meet our net zero emissions target quickly and at lowest cost to consumers and businesses. Backing cheap renewables is a clear example of the practical action to tackle climate change that the public is demanding, and this will speed up the transition to a net zero economy.

Today’s consultation outlines proposals to ensure the Contracts for Difference scheme can support the increased ambition required, including:

  • making the UK a world-leader in new technologies such as floating offshore wind, which would allow wind farms to be built further away from the shore and increase clean energy capacity
  • supporting our renewables supply chain to enhance productivity and increase competitiveness, boosting the UK’s world-class clean energy industry
  • improving the scheme to better support energy storage, so projects can provide power when the wind stops blowing or the sun is not shining

This is part of the Year of Climate Action, a defining year for our country and our planet, in the run up to the UK hosting the UN Climate Change Conference (COP26) in November.

Over 10% of NHS estate to switch to 100% renewable electricity in April in landmark deal

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NHS Property Services (NHSPS) has announced two new energy contracts via Inspired Energy. British Gas will provide 100% renewable electricity and Corona will provide natural gas to all their properties across England by April 2020.

NHSPS is responsible for around 10 per cent of the NHS estate, totalling more than 34 million sq ft, with over 3,500 properties and 5,000 employees, and is committed to actively making its sites more environmentally friendly.

By moving to 100% renewable electricity, NHSPS will offset over 40,000 tonnes of CO2 per year, demonstrating its dedication to tackling climate change while promoting sustainable practices with all its buildings.

The use of renewable electricity won’t increase costs to either NHSPS tenants or NHSPS itself. With the implementation of a new procurement strategy, as part of the new contracts, it will be able to deliver some of the best prices in the market, while managing risk and maintaining budget certainty.

The move follows the launch of the ‘For a greener NHS’ campaign and forms part of NHSPS helping to transform the NHS estate so that it can provide sustainably run buildings that help to deliver excellent patient care.

The NHS is currently responsible for around 4-5% of the UK’s carbon footprint. In September 2019, Simon Stevens, Chief Executive of NHS England, said the NHS would be accelerating its efforts to tackle climate change with a series of co-ordinated measures to reduce its carbon output – saying that the health service should also embolden staff to lead discussions with the public about wider measures needed to address climate change.

As well as switching to 100% renewable electricity by April 2020, NHSPS is also committing £1.5m in 2019/20 towards an LED upgrade programme, among other measures.

As well as being responsible for over 11% of the NHS estate itself, NHSPS provides property and facilities management expertise to the NHS. At a time of major change and increasing demand for the NHS, NHS Property Services is reducing costs, creating a more fit for purpose estate and generating vital funds, all of which are reinvested back into the NHS estate to support improvements in frontline patient care.

Commenting on the deal, Martin Steele, Chief Operating Officer at NHS Property Services, said: “Switching to 100% renewable electricity for all our buildings is a landmark moment in efforts to transform our NHS portfolio into a sustainable estate. We take our responsibility towards reducing the environmental impact of our buildings very seriously. This move will also help us to improve the wellbeing of our people and patients whilst reducing NHS operating and maintenance costs.”