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18 January 2018, in News, by Lewis Delicata

BS 7671 18th Edition Wiring Regulations due 1st July 2018

The BS 7671 Wiring Regulations written by the IET (The Institution of Engineering and Technology) set out the standards for electrical installations in the UK and many other countries. The IET plays a key role in electrical installation standards and safety, and is known for its independent and trusted voice. It manages the national committee JPEL/64 and publishes the IET Wiring Regulations BS 7671.

The 18th Edition of BS 7671 Wiring Regulations will be released on 1st July 2018, with the aim of being implemented on 1st January 2019.

Significant Changes due in BS 7671:2018

BS 7671 Wiring Regulations are mostly based on the IEC (International Electrotechnical Committee) and CENELEC (European Committee for Electrotechnical standardisation) standards. With every update made to BS 7671, a committee of experts and professional always considers any recent updates made to the International and European electrical installation standards.

Recently updates have been made to the IEC and CENELEC standards, which presents the perfect timing for the Wiring Regulations to be updated and harmonised.

The 18th Edition also includes a brand new section based around energy efficiency and the technology to install smart devices.

Changes to Section 722

Section 722 (electric vehicle charging installations) provides requirements for the supplies to electric vehicles. There are a number of significant changes in Section 722.

Protection against electric shock

Regulation 722.411.4.1 concerning the use of protective multiple earthing (PME) supply has changed. The exception for a dwelling if none of (i), (ii), or (iii) is reasonably practicable has been deleted. This now means that PME cannot be used unless you meet (i), or (ii), or (iii) of 722.411.4.1. As a reminder of those regulations:

  • Regulation 722.411.4.1(i) refers to a situation where a connecting point is supplied from a 3-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) refers to protection by a voltage operated device. An important change is that the regulation now makes the point that this device could be included within the charging equipment. It is worth noting that this device will also require an earth electrode.

The touch voltage threshold of 70 V mentioned in 722.411.4.1(i), 722.411.4.1(ii) and 722.411.4.1(iii) 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).

What is PME?

The Electricity Safety, Quality and Continuity Regulations 2002 (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 circuit protective conductors of the customer’s installation with Earth if the customer’s installation meets the requirements of BS 7671.

This 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. Whilst a protective multiple earthing 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.

External influences

In addition to IPX4 (protection against presence of water), Section 722 now requires IP4X as well to protect against presence of solid foreign bodies (AE3 – i.e. very small), and protection against impact (AG2 – i.e. medium severity).

Any wiring system or equipment selected and installed must be suitable for its location and able to operate satisfactorily without deterioration during its working life. Suitable protection must be provided, both during construction and for the completed installation.

RCD protection

Regulation 722.531.2.101 has been redrafted concerning RCD protection. The regulation now contains further requirements for both Type A and Type B RCDs to take account of DC fault current.

Socket-outlets and connectors

It is now required that where a BS 1363-2 socket-outlet is used for EV changing it must be marked ‘EV’ on its rear, except where there is no possibility of confusion, a label shall be provided on the front face or adjacent to the socket-outlet or its enclosure stating: ‘suitable for electric vehicle charging’.

Socket-outlets must be fit for purpose. They must be suitable for the load, and for the external influences such as protection against mechanical damage and ingress of water.

Changes to Section 753

Extension of scope – embedded electric heating systems for surface heating

The scope of Section 753 has been extended to apply to embedded electric heating systems for surface heating. They also apply to electric heating systems for de-icing or frost prevention or similar applications, and cover both indoor and outdoor systems. These include heating systems for walls, ceilings, floors, roofs, drainpipes, gutters, pipes, stairs, roadways and non-hardened compacted areas (for example, football fields, lawns). Heating systems for industrial and commercial applications complying with IEC 60519 and IEC 62395 are not covered.

Consequently, Section 753 now includes additional requirements to cover wall heating, heating conductors and cables where laid in soil and concrete etc. Additional requirements are also included to cover prevention of mutual detrimental influence.

Documentation is also covered. The designer will be required to provide appropriate information about approved substances in the surroundings of the heating units.

Additional requirements for wall heating systems

For wall heating systems (which may be more vulnerable than floors and ceilings from penetration) the standard contains additional requirements to protect against the effects of overheating caused by a short circuit between live conductors due to penetration of an embedded heating unit.

Regulation 753.424.101 requires that for wall heating systems the heating units shall be provided with a metal sheath or metal enclosure or fine mesh metallic grid. The metal sheath or metal enclosure or fine mesh metallic grid shall be connected to the protective conductor of the supply circuit.

Regulation 753.424.102 requires special care to be taken to prevent the heating elements creating high temperatures to adjacent material. This may be achieved by using heating units with temperature self-limiting functions or by separation with heat-resistant materials. Separation may be accomplished by placing on a metal sheet, in metal conduit or at a distance of at least 10 mm in air from the ignitable structure. A note adds that a larger separation distance may need to be considered depending on adjacent material.

Fire Protection

Since electricity was introduced to buildings, fire protection has been of paramount importance. RCDs can reduce the chance of fires associated with earth faults. However, whilst RCDs can detect earth faults they aren't able to reduce the risk of electrical fire due to series or parallel arcing between live conductors because there is no leakage current to earth. Details will be included in BS 7671:2018 for the installation of arc fault detection devices (AFDDs) to mitigate the risk of fire in final circuits of a fixed installation due to the effect of arc fault currents.

New section – energy efficiency

With global warming and reducing our consumption of energy becoming a big focus around the world, we have to consider how electrical installations can provide the required level of service and safety for the lowest electrical consumption. The draft proposals enable a client to specify the level of energy efficiency measures applied to an electrical installation. Installations can also be awarded points for energy efficiency performance levels, for example, transformer efficiency. These points can be added together with points for efficiency measures to give an electrical installation an efficiency class, ranging from EIEC0 to EIEC4, depending on the number of points awarded.