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Changes in the 18th edition of the IET Wiring Regulations primarily affect electrical designers and installers, but there are changes that are directly relevant to multidisciplinary building services projects, particularly where battery storage, smart building infrastructure, healthcare or energy management systems are involved.
For professionals, the key updates in BS 7671:2018+A4:2026 include a new chapter dedicated to stationary secondary batteries to support safe energy storage integration, alongside a new section addressing functional earthing and equipotential bonding for ICT systems.
Furthermore, the amendment introduces specific requirements for Power over Ethernet (PoE), to reflect its growing role in smart building infrastructure, and mandates a major revision to Section 710 concerning medical locations.
The IET Wiring Regulations BS 7671 have been used for the safe design and installation of low-voltage electrical installations in the UK since the 1880s. Since becoming a British Standard, they have been formally titled ‘Requirements for electrical installations’, as ‘regulations’ are now generally statutory and BS 7671, in itself, is not statutory. Because of the history of the document, however, the text will always be known as ‘the regs’.
As requirements, they are guidance, and there may be other ways of installing electrical services – but electrical installations that conform with the current BS 7671 are likely to achieve conformity with the relevant parts of the statutory Electricity at Work Regulations 1989, insofar as they apply, and there is a HSE note in BS 7671 to clarify this.*
BS 7671 is produced and revised by the IET and the BSI. Committees and sub-committees have representatives from most of the industry bodies, and CIBSE is represented by members of the CIBSE Electrical Services Group.
Some of the more relevant technical updates in Amendment 4 are below.
Fire safety
Chapter 42: Protection against thermal effects
Regulation 422.2 (Protected escape routes) has been modified slightly. Cables that meet the requirements of Regulation 422.2.1 can be installed in a protected corridor. In addition, cables installed in a fire-resisting enclosure are now deemed to be outside the protected escape route. Regulation 422.2.1 now lists the cables permitted for installation in protected escape routes.
Section 521: Types of wiring system
A note has been added clarifying the intent of Regulation 521.10.202. Wiring systems are to be supported such that they will not be liable to premature collapse during fire and trap people.
Section 537: Isolation and switching
Regulation 537.4.2 has been redrafted and firefighters’ switches are now required in locations specified by the fire engineer to support the building’s overall fire strategy.
Chapter 56: Safety services
Chapter 56 has been updated and aligned with other current BSs.
Appendix 13: (Informative) Escape routes and fire protection
The guidance in the first part of Appendix 13 (Cables in protected escape routes) has been redrafted to take account of BS 9991 and BS 9999, and a fire safety strategy is to be prepared by the fire engineer based on appropriate guidance.
Energy transition (battery storage and bidirectional power)
Section 551: Low-voltage generating sets
Regulation 551.7.1 has been redrafted. An indent (c) has been added, which requires a suitable protective device where energy flow is bidirectional. An indent (d) has also been added, which prohibits the connection of a source to the load side of an RCD under certain conditions.
Regulation 551.7.2 has been redrafted to form two regulations. Regulation 551.7.2.1 requires the generating set to be installed on the supply side of all protective devices and that stationary batteries (Chapter 57) be considered a generating set, not a load. Regulation 551.7.2.2 sets out the requirements for the low-voltage switchgear and controlgear assembly when a generating set is used as an additional source of supply, in parallel with another source, and is connected via LV switchgear.
Chapter 57: Stationary secondary batteries
A new chapter, this deals with requirements for stationary secondary battery installations where the designed purpose is for storage and supply to electrical installations.
Digital buildings (Power over Ethernet)
Section 716: Power over Ethernet
This new section deals with requirements for the distribution of ELV DC power using balanced, information technology cables and accessories primarily designed for data transmission, as specified in BS EN 50173-1, using power feeding sourcing equipment in accordance with BS EN IEC 62368-3.
Critical environments (medical locations)
Section 710: Medical locations
There is a major revision of the section, with requirements for independent supplies in medical locations of group 2 and the inclusion of a schedule of test results for recording the resistance of supplementary protective equipotential bonding conductors.
Energy efficiency
Chapter 81: Low-voltage electrical installations Part 8-1: Functional aspects – energy efficiency
A new Chapter 81 concerning energy efficiency has been introduced. This refers the reader to the Building Regulations for England and Wales, Scotland, and Northern Ireland for guidance on the requirements. The chapter also refers the reader to BS HD 60364-8-1:2019, Low-voltage electrical installations Part 8-1: Functional aspects – Energy efficiency. The guidance previously given in Appendix 17 has been deleted.
Appendix 17 (Informative) Energy efficiency
This appendix has been deleted and a new Chapter 81, concerning energy efficiency, has been introduced instead.
Cable installation and sizing
Section 536: Coordination of electrical equipment for protection, isolation, switching and control
Regulation 536.4.202 has been redrafted and now covers the coordination between low-voltage switchgear and controlgear assembly and the overload protective device. The regulation now contains load curtailment as one of the conditions to be satisfied.
Appendix 4: Cable ratings
The reference methods for buried cables have been updated. Distinct methods and corresponding current-carrying capacities now apply based on whether the cable is installed in direct contact with soil or enclosed within a conduit or duct. Tables 4A2, 4D4A, 4E4A, 4H4A and 4J4A have been revised to reflect these changes.
Compliance, CPD and reporting
Chapter 65: Periodic inspection and testing
Regulation 653.1 now requires the notes for the person producing the report (provided in Appendix 6) to be taken into account on the Condition Report. Regulation 653.2 now requires the report to include guidance for the recipient(s) based on the model in Appendix 6. A note has also been added pointing out that photographic and/or thermographic images can be appended to the report.
Appendix 6: (Informative) Model forms for certification and reporting
The notes for the person producing the condition report have been redrafted. Items have been rearranged for clarity.
Training and experience
As this Amendment 4 does not have significant new requirements, it has generally been considered that electrical operatives carrying out installation works do not require a specific new qualification. But they must be aware of the requirements in the new Amendment relevant to their work, especially if they are a qualified supervisor or duty holder, or supervising operatives or helping to train apprentices.
General CPD or regular toolbox talks should be encouraged to inform operatives of the amendments and assess their understanding. As required in the Electricity at Work Regulations 1989, people carrying out work must be competent or properly supervised.
Engineers or designers may require formal training and qualifications, depending on their work, and, again, must be competent or properly supervised. CPD, by itself, may not be adequate.
Although Amendment 4 introduces relatively few fundamental design changes, it reflects the continuing evolution of electrical installations as buildings become increasingly electrified, digitalised and integrated with renewable energy systems.
Please contact BSI if you identify an inaccuracy, ambiguity, gap or technical inconsistency in any standard.
About the author
Leon Markwell MCIBSE is senior engineer at IET and chair of the CIBSE Electrical Services group
NOTES
This HSE note infers that where a design may fall outside the remit of BS 7671, requires Building Regulations special requirements, has specific external influences beyond those referenced in BS 7671, or requires a higher degree of design requirements, as evidenced by a robust and suitable risk assessment, because of the respective installations’ usage or design, the designer and installation duty holder must account for this (the duty holder carries the legal, statutory responsibility for health and safety under UK law, under the Electricity at Work Regulations 1989).