Understanding BS 7671:2018+A4:2026 Wiring Regulations

BS 7671:2018+A4:2026 | A Technical Review of the Latest Wiring Regulations

Published: May 2026 | Industry Insights by TMUK Group Ltd

On 15 April 2026, the IET and BSI officially published **Amendment 4 (A4:2026)** to the 18th Edition Wiring Regulations. This update represents the most significant shift in UK electrical standards since the 2018 release, specifically targeting the rapid integration of renewable energy storage, smart building technology, and advanced healthcare safety.

As of today, Amendment 4 can be implemented immediately. For all new designs and installations commissioned after **15 October 2026**, compliance with the latest standards is mandatory. The previous consolidated version (A3:2024) will be formally withdrawn on that date.

1. New Chapter 57: Stationary Secondary Batteries

The most consequential update is the introduction of **Chapter 57**, which provides the first dedicated regulatory framework for stationary secondary batteries used for energy storage and supply. With the surge in Solar Photovoltaic (PV) installations and commercial Energy Storage Systems (ESS), these regulations formalise safety requirements that previously existed only in fragmented best-practice guides.

• Location Restrictions: New regulations strictly prohibit the installation of battery storage in specific high-risk areas, such as lofts and designated escape routes in residential settings.
• Thermal Management: Mandatory requirements for fire-risk mitigation, including thermal runaway protection and specific ventilation provisions to prevent gas buildup.
• Bi-directional Protection: Advanced rules for hybrid and bi-directional inverters, ensuring protective devices are correctly coordinated for current flow in both directions.

2. Section 716: Power over Ethernet (PoE)

Smart building technology now frequently utilises data cabling to power low-wattage devices like LED lighting, sensors, and access control. Amendment 4 introduces **Section 716**, bringing PoE under the official scope of BS 7671.

• Thermal Derating: Electricians must now account for the heat buildup in dense cable bundles carrying PoE feeds. Derating factors must be applied to ensure the current-carrying capacity of data cables is not compromised.
• Voltage Limits: Clear requirements for SELV and PELV systems to ensure safe operation alongside standard 230V infrastructure.

3. Major Revision of Section 710 (Medical Locations)

To align with current NHS requirements and specialist sector risks, Section 710 has undergone a full revision. The primary focus is on enhanced safety and the verification of protective measures in patient-critical environments.

• Resistance Recording: Introduction of a mandatory schedule of test results to record the exact resistance of supplementary protective equipotential bonding conductors (measured in Ω).
• Continuity Requirements: Strengthened criteria for the electrical continuity of bonding to ensure patient safety during a fault condition.

4. Section 545: Earthing for ICT Systems

The standard now distinguishes between protective earthing (for safety) and **functional earthing** (for signal integrity). Section 545 provides requirements for functional-equipotential-bonding in information and communication technology systems, reducing the impact of electromagnetic interference (EMI) in data-rich environments.

5. Evolution of Periodic Inspection (EICR)

Amendment 4 introduces a significant change to the classification of Periodic Inspection and Testing results:

• The FI Code Change: The “Further Investigation” (FI) code no longer automatically renders an Electrical Installation Condition Report (EICR) “Unsatisfactory”. This allows for a more nuanced engineering judgement based on the specific nature of the investigation required.
• Evidence-Based Reporting: Inspectors are now encouraged to append thermographic and photographic evidence to reports to provide a clearer compliance narrative for the recipient.

Important Transition Deadlines

Is Your Facility Ready for Amendment 4?

TMUK Group Ltd remains at the forefront of regulatory compliance. Our engineering teams are already operating to Amendment 4 standards to ensure our clients’ infrastructure is future-proofed against evolving legislation.

Contact our Technical Team for a Compliance Review:

info@tmuk.org | 01384 901117

Kevin McCallum

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