Category Archives: 18th Edition Regulations

Can I install a metal consumer unit with a TT earthing system?

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High earth fault loop impedance values associated with TT earthing systems mean the earth fault current level is unlikely to be sufficient to operate the distributor’s protective device within the permitted time of 1 second, as required in Regulation 411.2.4, or at all in some cases, depending on Earth resistance values.

There is nothing to prevent a metal consumer unit being installed with a TT earthing system, but it’s important to ensure that an earth fault cannot develop between the meter tails and the metallic enclosure before the RCD.

Methods of reducing an earth faults include keeping the meter tails as short as possible, the installation of proprietary clamps and glands to secure the cables and prevent strain on the terminations, minimising the risk of damage to the meter tails and a subsequent earth fault.

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

New amendment to BS 7671 (IET Wiring Regulations) Amendment 1

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The IET has announced a new amendment to BS 7671:2018 (IET Wiring Regulations 18th Edition). The national Wiring Regulations committee, JPEL/64, agreed the publication of Amendment 1, which will consist of a stand-alone update to Section 722: Electric Vehicle Charging Installations.

The amendment, which is due to publish in early 2020, will be free to view on the IET website, and only form part of a consolidated new Regulations following the next major amendment to BS 7671, expected in 2022.

The amendment follows advances in technology that were not available when BS 7671:2018 published, enabling a more practical solution for the installation of charging points. Functionality built directly into charging equipment uses existing technology, but employed in a new way, allowing charging points to be deployed more widely than ever before.

The updated Section 722 will make installing charging points quicker and easier, and will reduce the cost of installations for both installers and consumers.

The UK government is investing £400 million to accelerate the roll-out of charging infrastructure to help meet its target of at least 50% of new car sales to be ultra-low emission by 2030*.

Mark Coles, Head of Technical Regulations at the IET, is proud of the way that JPEL/64 has been able to respond to the changes in technology. He explains: “JPEL/64 has been able to address a new opportunity for electric vehicle charging equipment that provides a practical, cost-saving solution benefiting industry, consumers and government alike, to help the UK lead the way in the roll-out of infrastructure to support the electric vehicle revolution.

“This update to the IET Wiring Regulations puts the electrical industry at the forefront of driving technological innovation to ensure the installation of practical, safe charging points that are accessible to all.

“By producing Amendment 1 to BS 7671:2018 as a stand-alone, free-to-view document, this updated Section 722 will reach industry much quicker than a full, consolidated amendment would allow, enabling installers to take advantage of BS 7671:2018+A1:2020 as soon as possible.”

Keep an eye on theiet.org/updates to for information on the Draft for Public Comment and publication information.

Proposed timeline

  • 04 September 2019: Amendment 1 approved by JPEL/64
  • October 2019: The Draft for Public Comment for Amendment 1 will be available for 60 days to allow industry to respond to the proposed changes (see theiet.org/updates for details)
  • January 2020: Amendment 1 will publish as a free-to-view document on the IET website and come immediately into effect, eschewing the usual 6-month adjustment period to ensure industry can immediately take advantage of the changes

BS 7671:2018 – Section 708 (caravan/camping parks) And Section 721 (caravan and motor caravans)

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Section 708 caravan/camping parks

This particular requirement of 708 applies to the electrical installations in caravan/camping parks and similar locations providing connection points for supplying leisure accommodation vehicles (including caravans) and tents.

The scope of Section 708 has been extended to cover circuits intended to supply residential park homes in caravan parks, camping parks and similar locations. In addition changes have been made to socket outlet requirements, RCD protection, and external influences.

Protection against electric shock

General requirements

As you would expect the protective measures of obstacles; placing out of reach, in a non-conducting location and protection by earth-free local equipotential bonding are not permitted. These measures are contained in Sections 417 and 418 of BS 7671:2008 and are not for general application. The protective measures of section 417 provide basic protection only and are for application in installations controlled or supervised by skilled or instructed persons. The fault protective provisions of Section 418 are special and, again, subject to control and effective supervision by skilled or instructed persons.

Protective multiple earthing

As stated in Regulation 708.411.4 The Electricity Safety, Quality and Continuity Regulations 2002 (ESQCR) prohibit the connection of a PME earthing facility to any metalwork in a leisure accommodation vehicle (including a caravan).

This does not preclude the use of a PME earthing facility as the means of earthing for other purposes, such as to the installations of permanent buildings.

External influences

Any wiring system or equipment selected and installed must be suitable for its location and able to operate satisfactorily during its working life. Suitable protection must be provided, both during construction and for the completed installation. Regarding presence of solid foreign bodies, a minimum degree of protection of IP4X is now required. Regarding presence of water a minimum degree of protection of IPX4 is required.

Equipment must be protected against mechanical impact IK 08 (see BS EN 62262) and/or located to avoid damage by any reasonable foreseeable impact.

Caravan pitch socket-outlets

The requirements for socket outlets have been redrafted to prevent the socket contacts being live when accessible.

Regulation 708.55.1.1 requires that every socket-outlet or connector shall either comply with:

  1. a) BS EN 60309-2 and shall be interlocked and classified to clause 6.1.5 of BS EN 60309-1:1999 to prevent the socket contacts being live when accessible; or

 

  1. b) – be part of an interlocked self-contained product complying with BS EN 60309-4 and classified to clauses 6.1.101 and 6.1.102 of BS EN 60309-4:2006 to prevent the socket contacts being live when accessible.

The current rating is to be not less than 16 A but may be greater if required. At least one socket-outlet should be provided for each caravan pitch. Where socket-outlets are grouped in pitch supply equipment, there should be one socket-outlet for each pitch limited to a group of four.

 Overcurrent protection

Every socket-outlet shall be individually protected by an overcurrent protective device, in accordance with the requirements of Chapter 43.

A fixed connection for a supply to a mobile home or residential park home shall be individually protected by an overcurrent protective device, in accordance with the requirements of Chapter 43.

Isolation

Regulation 708.537.2.1.1 now requires at least one means of isolation to be installed in each distribution enclosure. This device shall disconnect all live conductors.

RCD protection

Each socket-outlet must be protected individually by an RCD having a rated residual operating current not exceeding 30mA. The RCD must disconnect all live conductors including the neutral.

Requirements for RCD protection have been extended to cover supplies to residential park homes. A final circuit (from the metering point) intended for the

fixed connection for a supply to a mobile home or a residential park home shall be individually protected by an RCD having a rated residual operating current not exceeding 30 mA accessible to the consumer. Devices selected shall disconnect all live conductors.

PME

As mentioned previously, the ESQCR prohibit the connection of a PME earthing facility to any metalwork in a leisure accommodation vehicle (caravan). If the caravan supply is derived from a permanent building that is supplied by a PME system then the caravan supply will have to be part of a TT system having a separate connection to Earth independent from the PME earthing.

The separation of the earthing can be effected at the main distribution board. The IET’s Guidance Note 7 publication Special Locations provides detailed information. This enables the exposed-conductive-parts connected to each system to be more readily identified and inspected periodically. An earth electrode for the TT system should be provided nearby and located so that the resistance areas of the PME supply earthing and earth electrode do not overlap.

Alternatively, the separation of the earthing can be made at the caravan pitch supply points. In this instance, earth electrodes will be required at these points.

Again, The IET’s Guidance Note 7 provides detailed information.

Section 721 caravans and motor caravans

The particular requirements of 721 apply to the electrical installations of caravans and motor caravans at nominal voltages not exceeding 230/440 V AC or 48 V DC

Note there are some exceptions.

This section contains a number of changes including requirements for electrical separation, RCDs, proximity to non-electrical services, and protective bonding conductors.

Protective equipotential bonding

Regulation 721.411.3.1.2 requires structural metallic parts that are accessible from within the caravan to be connected through main protective bonding conductors to the main earthing terminal within the caravan.

The requirements for connections of protective bonding conductors have been clarified. Regulation 721.544.1.1 states that the terminations of protective bonding conductors connecting the conductive structure of the unit shall be accessible and protected against corrosion.




Provision of RCDs

The requirements for RCD protection have also been redrafted.

Regulation 721.415.1 states that where protection by automatic disconnection of supply is used, a residual current device with a rated residual operating current not exceeding 30 mA, complying with BS EN 60947-2 (Annex B), BS EN 61008-1, BS EN

61009-1 or BS EN 62423 breaking all live conductors, shall be provided having the characteristics specified in 415.1.1.

Each supply inlet shall be directly connected to its associated RCD.

Please note this implies that there may not be any taps or junctions in this connection.

An RCD is a protective device used to automatically disconnect the electrical supply when an imbalance is detected between live conductors. In the case of a single-phase circuit, the device monitors the difference in currents between the line and neutral conductors. If a line to earth fault develops, a portion of the line conductor current will not return through the neutral conductor. The device monitors this difference, operates and disconnects the circuit when the residual current reaches a preset limit, the residual operating current (IΔn).

Proximity to non-electrical services

The requirements for proximity to non-electrical services have been redrafted.

Regulation 721.528.2.1 requires that where cables have to run through a gas cylinder storage compartment, they shall pass through the compartment at a height of not less than 500 mm above the base of the cylinders and shall be protected against mechanical damage by installation within a conduit system complying with the appropriate part of the BS EN 61386 series or within a ducting system complying with the appropriate part of the BS EN 50085 series.

Switchgear and controlgear

The installation to the caravan should have a main disconnector, which will disconnect all the live conductors. This should be placed in a suitable position for ready operation within the caravan to isolate the supply. When a caravan only has one final circuit then the isolation can be afforded by the overcurrent protective device as long as it fulfils the requirements for isolation.

An indelible notice in the appropriate language(s) must be permanently fixed near the main isolation point inside the caravan to provide the user with instructions on connecting and disconnecting the supply (refer to Figure 721 of BS 7671).

The inlet to the caravan must be an appliance inlet complying with BS EN 60309-1. This should be installed not more than 1.8 m above ground level, in a readily accessible position, have a minimum degree of protection of IP44, and should not protrude significantly beyond the body of the caravan.

The connecting flexible cable

The means of connecting the caravan to the pitch socket-outlet should be provided with the caravan. This must have a plug at one end complying with BS EN 60309-2, a flexible cable with a continuous length of 25 m (±2 m). The connecting flexible cable must be in one length, without signs of damage, and not contain joints or other means to increase its length; and a connector if needed that is compatible with the appropriate appliance inlet. The cable should be to the harmonized code H05RN-F (BS EN 50525-2-21) or equivalent, include a protective conductor, have cores coloured as required by Table 51 of BS 7671 and have a cross-sectional area as shown in Table 721.

Periodic inspection & testing

The purpose of periodic inspection and testing is to provide an engineering view on whether or not the installation is in a satisfactory condition where it can continue to be used safely. Periodic inspection and testing is necessary because all electrical installations deteriorate due to a number of factors such as damage, wear, tear, corrosion, excessive electrical loading, ageing and environmental influences. IET Guidance Note 3 gives the recommended initial frequencies for inspection of electrical installations for construction sites, caravan/camping parks, and in caravans.

Conclusion

It is important to be aware that this article (which is based on an article from Issue 67 of Wiring Matters) only gives a brief overview of requirements for electrical installations on caravan/camping parks, and in caravans. Refer to BS 7671:2018 for more information.

Order Now – Eighteenth Edition – BS 7671:2018 (Electrical Regulations)

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You can now order your copy of the Requirements for Electrical Installations, IET Wiring Regulations, Eighteenth Edition, BS 7671:2018 (Electrical Regulations) and the On-Site Guide (BS 7671:2018) (Electrical Regulations) 

Requirements for Electrical Installations, IET Wiring Regulations, Eighteenth Edition, BS 7671:2018 (Electrical Regulations)

The IET Wiring Regulations are of interest to all those concerned with the design, installation and maintenance of electric wiring in buildings. The market includes electricians, electrical contractors, consultants, local authorities, surveyors and architects. This book will also be of interest to professional engineers, as well as students at university and further education colleges. All users of the IET Wiring Regulations need to be aware of the coming changes in the 18th Edition (BS 7671:2018). This is intended to come into effect on 1st January 2019, although industry needs to start preparing for this from its point of publication (2nd July 2018).

On-Site Guide (BS 7671:2018) (Electrical Regulations) Spiral-bound – 2 Jul 2018

The On-Site Guide is an essential guide to BS 7671. It incorporates the extensive changes in BS 7671:2018, making this a vital guide for keeping up to date. It enables the competent electrician to deal with installations (up to 100 A, 3-phase) providing essential information in a convenient, easy-to-use format. The 18th Edition IET Wiring Regulations publishes in July 2018 and comes into effect on 1st January 2019. All new installations from this point must comply with BS 7671:2018.

     

All above links on this page offer you the ability to order the above publications via Amazon directly.