1. 18th Edition

The 18th Edition (BS 7671:2018) is launched

BS 7671:2018 was issued on the 2nd July 2018 and is intended to come into effect on 1st January 2019. Installations designed after 31st December 2018 are to comply with BS 7671:2018.

In this article Geoff Cronshaw answers some of the typical questions that are raised and look at the impact that some of the changes introduced by the 18th Edition will have on the industry. We focus on electric vehicle charging, surge protection, and arc fault detection.


The IET often gets asked why is there a new edition or amendment to the IET Wiring Regulations (BS 7671). The IET Wiring Regulations (BS 7671) are based on European Standards which in turn are usually based on International Standards. As the UK is a Member of CENELEC (the European Standards organisation) the UK have to implement the technical intent of published CENELEC Harmonisation documents. The CENELEC Harmonisation documents are regularly updated to keep pace with new emerging technology such as electric vehicle charging, surge protection and arc fault detection.

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 of the 18th Edition.

Protection against electric shock

Regulation 722.411.4.1 concerning the use of a 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.

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) 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.

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), and protection against impact (AG2).

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 charging 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 the requirements concerning surge protection

Clause 443 of the 18th Edition (BS 7671:2018) deals with the protection of electrical installations against transient overvoltages (surge protection) of atmospheric origin transmitted by the supply distribution system, and against switching overvoltages generated by the equipment within the installation. Clause 443 contains significant changes.

The AQ criteria (conditions of external influence for lightning) for determining if protection against transient overvoltage is needed is no longer included in BS 7671. Protection against transient overvoltage now has to be provided where the consequence caused by overvoltage affects:

  1. serious injury to, or loss of, human life
  2. interruption of public services and/or damage to cultural heritage
  3. interruption of commercial or industrial activity, and
  4. interruption affects a large number of collocated individuals.

For all other cases, a risk assessment would have to be performed in order to determine if protection against transient overvoltage is required. If the risk assessment is not performed, the electrical installation will have to be provided with protection against transient overvoltage.

However, an exception not to provide protection is included for single dwelling units where the total value of the installation and equipment therein, does not justify such protection.

There are different types of SPDs. Type 1 are generally installed at the origin of the installation and type 2 are generally installed at distribution boards within the installation.  It is important that SPDs are selected and installed in accordance with the manufacturer’s instructions.

The introduction of arc fault detection

Protection against fire

Protection against fire resulting from the electrical installation and the use of the electrical installation has been necessary ever since electricity was first introduced into buildings. Chapter 42 of the 18th Edition contains the requirements for the protection of persons, livestock and property against fire caused by electrical equipment, against burns and overheating and for including precautions where particular risks of fire exist.

The 18th Edition now recommends 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. The 18th Edition gives examples of where such devices can be used as follows:

  1. premises with sleeping accommodation
  2. locations with a risk of fire due to the nature of processed or stored materials, i.e. BE2 locations (e.g. barns, woodworking shops, stores of combustible materials)
  3. locations with combustible constructional materials, i.e. CA2 locations (e.g. wooden buildings)
  4. fire propagating structures, i.e. CB2 locations, and
  5. locations with endangering of irreplaceable goods.

Arcs can be caused by Insulation defects in cables, damage to cables by impact and penetration of nails and screws, loose terminal connections etc. Switching arcs caused by fluorescent lighting, for example, should not cause the AFDD to operate.

An AFDD is designed to operate (trip) when a dangerous arc is detected by analysing the signature of an arc. AFDDs can be installed in distribution boards and consumer units to protect final circuits. AFDDs should be installed in accordance with the manufacturer’s instructions. When installing components of a different manufacturer to the existing equipment in a distribution board or consumer unit it is important to seek advice from the manufacturer that the new equipment is suitable and compatible.


Section 710 (medical locations) contains particular requirements.

Regulation 710.421.1.201 states: “In medical locations of Group 1 and 2 Arc Fault Detection Devices (AFDDs) are not required to be installed. In medical locations of Group 0 Arc Fault Detection Devices (AFDDs) shall be used subject to a risk assessment.”


Important: this article only gives a brief overview of some of the changes within the 18th Edition (BS 7671:2018). For more information refer to BS 7671:2018.