Amendment 4 to the 18th Edition Wiring Regulations

By AM Specialists Group Ltd 19th October 2026

The Institution of Engineering and Technology (IET) and the British Standards Institution (BSI) have published Amendment 4:2026 to BS 7671:2018, the 18th Edition of the IET Wiring Regulations. The update introduces changes affecting battery storage, Power

What is Amendment 4?

BS 7671 sets out requirements for designing, installing, inspecting and testing electrical installations in the UK. Amendment 4 updates the 18th Edition to reflect developments in electrical technology and modern installation practices.

The revised standard, BS 7671:2018+A4:2026, replaces the previous version incorporating Amendments 2 and 3.

Key changes introduced

1. Battery storage

New Chapter 57 covers stationary secondary battery installations used to store and supply electrical energy. Contractors should review requirements for installing and protecting these systems, alongside relevant fire safety guidance and manufacturer instructions.

2. Power over Ethernet

New Section 716 addresses systems distributing extra-low-voltage DC power through information technology cables. Contractors working with PoE should familiarise themselves with the applicable installation and verification requirements.

3. ICT earthing and bonding

Section 545 introduces updated requirements for functional earthing and equipotential bonding in information and communication technology (ICT) systems. These changes are relevant to buildings with extensive communications infrastructure and electronic equipment.

4. Medical locations

Section 710 has undergone substantial revision, including changes relating to power supplies, medical insulation monitoring and supplementary equipotential bonding. Contractors working in healthcare environments should review the revised provisions and update inspection and testing procedures where necessary.

What should electrical contractors do?

Businesses should review their compliance arrangements and identify any changes required. Key actions include:

Update technical resources: Ensure staff have access to the current edition of BS 7671.
Review competence: Identify training needs for electricians, designers, inspectors and testers.
Check procedures: Review installation, inspection and testing processes.
Update documentation: Ensure project specifications and quality assurance records reflect applicable requirements.
Inform subcontractors: Communicate relevant changes across the supply chain.

Does Amendment 4 apply retrospectively?

The revised standard does not automatically require upgrading every existing electrical installation. An installation compliant with an earlier edition is not necessarily unsafe simply because the regulations have changed.

However, contractors should establish which requirements apply when undertaking new installations, additions or alterations, considering the circumstances and relevant legal obligations.

Preparing for compliance

Amendment 4 reflects the evolving demands of electrical installations, particularly as battery storage and connected technologies become more widespread.

Reviewing technical resources, staff competence and compliance documentation can help contractors identify gaps and prepare for the requirements relevant to their work.

For detailed guidance, consult the IET and the full text of BS 7671:2018+A4:2026.