18th Edition Wiring Regs: Changes at a Glance for Test and Measurement


The 18th Edition of the BS7671 Wiring Regulations has been finalised by the IET and will be issued on 2nd July 2018. It is set to supersede the previous 17th edition on 1st January 2019 and contains multiple changes, although not all of these are pertinent to test and measurement.

RCD Protection

The 18th Edition is characterised by increased prevalence of protective RCDs in a range of installations so there will be greater need for RCD testers and MFTs with a reliable RCD testing function. In particular, <30mA RCDs will now be a requirement on sockets rated up to 32A (unless deemed unnecessary by a risk assessment) rather than just 20A (411.3.3), whilst they will also be needed on all AC final circuits supplying luminaires within residential buildings (411.3.4). It is also important to note that Table 41.1 now applies to final circuits rated up to 63A (with sockets attached) so maximum disconnection times will apply to a greater number of circuits, thus requiring accurate testing with appropriate equipment.

Switching and Isolation

The new Chapter 46 of the 18th Edition Wiring Regulations discusses non-automatic local and remote isolation and switching when these measures are used to prevent or remove dangers associated with electrical installations and equipment. It also deals with switching used to control circuits and equipment although any circuits or equipment that come under BS EN 60204 are solely covered by that standard. Further changes have been made in chapter 56 which deals with protection, isolation, switching, control and monitoring.

Earthing Systems

There are several changes to earthing systems contained within the 18th Edition. Newly introduced regulations 542.2.3 and 542.2.8 define new requirements for earth electrodes whilst two further regulations (543.3.3.101 & 543.3.3.102) cover the installation of switching devices in protective conductors. The latter section refers to protective conductors in installations supplied by multiple power sources.

Overvoltage Protection

One of the most significant changes in the 18th edition is the overhaul of Section 443 which deals with overvoltage caused by atmospheric conditions, i.e. lightning. Where the need for protection against transient overvoltage used to be defined by the AQ criteria - effectively considering the frequency and likelihood of lightning strikes - these have now been replaced by criteria considering the potential consequences of lightning strikes. This will expand the scope where protection is required, except in certain single dwelling units, and once again these additional systems will need to be thoroughly tested.

Specialist Installations

Various specialist installations have been introduced into the scope of BS7671 whilst the regulations surrounding others have been modified. Of particular note to test and measurement, there will be new requirements for electrical installations in caravan/camping facilities (Section 708); installations in caravans and motor caravans (Section 721); and electric vehicle charging points (Section 722). A particular requirement for B-type RCDs in charging points and a repeal of exemptions for PME supplies are important and may require updated equipment.

Floor and Ceiling Heating Systems

Section 753 has been revised and now deals with all embedded electrical systems for surface heating. In addition to heating, other applications such as de-icing and frost prevention are now included within the section and both indoor and outdoor systems are considered.

Stay Tuned for the Full 18th Edition

This is just a summary of some of the main changes now that the 18th Edition has been finalised. A number of modifications and introductions have been made to other chapters which will have major implications on the design and installation of electrical systems although they may not directly involve different testing practices. It is therefore vital to make sure you are up to date on requirements before the 17th Edition is formally replaced at the beginning of 2019.