Last edited 12 May 2021

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ECA Institute / association Website

18th Edition Wiring Regulations

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[edit] Introduction

With the introduction of the 18th Edition Wiring Regulations in 2018, electricians are expected to perform all work in accordance with the changes, updates and corrections that came into effect since the 17th Edition.

Some of the changes have proven harder to implement than others. A significant set of corrections was published in December 2018 (outlined below).

From its member helpline, the Electrical Contractors' Association (ECA) has picked a few of the most frequently asked questions and summarised them below:

[edit] Residual current devices (RCDs)

Chapter 41 - protection against electric shock, Regulation 411.3.4

The application of RCDs was expanded and revised for certain situations. The Regulation now requires that, within domestic premises, additional protection by an RCD shall be provided for AC final circuits supplying luminaires.

This was new, and most likely a response to the many new ways we now use lighting in our homes, with the introduction of LEDs, advanced lighting displays, and the fact that consumers are now able to purchase luminaires and put them up themselves.

Another change sees the period between testing RCDs (by pushing the ‘T’ or ‘Test’ button) increased from ‘quarterly’ to ‘six-monthly’, which means that the task can be conveniently done when the clocks are changed.

[edit] Arc fault detection devices

Chapter 42 - protection against thermal effects, Regulation 421.1.7

This new regulation recommends that arc fault detection devices (AFDDS) are installed to help mitigate the risk of fire in AC final circuits in the event of arc faults. They are recommended for premises with sleeping accommodation, and locations with risk of fire due to the nature of processed or stored materials, such as barns, woodworking shops, or stores of combustible materials.

[edit] Surge protection devices

Chapter 44 - Protection against voltage disturbances and electromagnetic disturbances, Regulation 443.4

This amended section now stipulates that protection against overvoltage by means of surge protection devices (SPDs) has to be provided. This is applicable where the consequence of an overvoltage would result in serious injury or loss of life, serious disruption of public services, interruption of industrial activity, or if it would affect a large number of co-located individuals.

[edit] Electric vehicles

Section 722 - electric vehicle charging installations

These changes are relatively small, but they will have big implications. Particularly for charging points installed at a dwelling, outside a building, on a TN-C-S earthing system. As with other changes, these are to keep the UK’s standards in tandem with the technical intent of worldwide standards.

In the 18th Edition, the option to use a protective multiple earthing (PME) facility has been reduced. There are ways that PME can be used, but these are often difficult to achieve. Therefore, most installations will rely on separation of the earthing system and making the electric vehicle (EV) a TT system (using an electrode in the ground).

Newly recognised types of RCDs are specifically picked up in section 722 for EVs, but general awareness of these in the wider industry is very low. The new devices are electronic in nature and have a different reaction to circuits containing power electronics that can distort the waveform. The industry and its customers are only just becoming aware of these products, the costs are high in comparison to existing devices, and availability is limited.

[edit] December 2018 Corrections

In December 2018, 11 corrections to the 18th Edition were published in a corrigendum. Some of these include:

  • Five labels oversized in Section 514;
  • A new colour is available to identify a functional earthing conductor;
  • Update regarding alignment of a zone in Figure 701.1f to match the words detailed in Regulation 701.32.3;
  • In medical locations of group 1 and group 1, a minimum of two lighting circuits shall be provided from separate sources of supply;
  • Change to the zone markings in Fig 701.1f;
  • Appendix 4 last row of the table covers 90 ºC 'thermosetting' cables, and not thermoplastic cables;

There are many other changes within the 18th Edition. Find out more about the changes, relevant training and other updates at

[edit] About this article

This article was written by Gary Parker, ECA Senior Technical Support Engineer. It was previously published under the title 'Refresh your 18th Edition knowledge this bank holiday' on the ECA website in August 2019 and can be accessed HERE.

[edit] Related articles on Designing Buildings Wiki


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