Introduction
In April 2026, the Institution of Engineering and Technology (IET) and the British Standards Institution (BSI) published Amendment 4 (2026) to BS 7671:2018 — the UK’s national standard for electrical installation safety, better known as the IET Wiring Regulations (18th Edition).
This is not a minor housekeeping update. Amendment 4 introduces substantial changes across several areas of electrical safety, incorporating new technologies that have reshaped the industry over the past few years — from energy storage systems to Power over Ethernet infrastructure. For builders, electrical contractors, and site managers, understanding what has changed is not optional. The previous version of the standard is being withdrawn six months from the amendment’s publication date.
This guide explains what has changed, who it affects on construction sites, and what practical steps you need to take to stay compliant.
What Is BS 7671 and Why Does It Matter to Builders?
BS 7671 is the UK national standard that sets out the requirements for electrical installations in buildings and construction sites. It underpins almost every aspect of electrical safety on a build — from temporary site distribution boards and generator connections to permanent wiring in completed structures.
Compliance with BS 7671 is a legal expectation, not merely best practice. The Electricity at Work Regulations 1989 require that all electrical systems are constructed, maintained, and operated to prevent danger. On construction sites specifically, the Construction (Design and Management) Regulations 2015 (CDM 2015) require that electrical safety is addressed within the Construction Phase Plan. Any electrical installation — temporary or permanent — that does not meet the current edition of BS 7671 creates a compliance risk and, more importantly, a genuine safety risk to workers and future occupants.
Amendments to BS 7671 are issued to keep the standard aligned with new technology, updated European and international standards, and lessons learned from real-world incidents. When an amendment is published, electrical professionals are expected to familiarise themselves with the changes and apply them to new work.
What Has Changed in Amendment 4 (2026)?
1. Stationary Secondary Batteries — A New Chapter
One of the most significant additions in Amendment 4 is a dedicated chapter covering stationary secondary batteries. This reflects the rapid growth of battery energy storage systems (BESS) on commercial and residential construction projects, as well as on construction sites themselves where battery storage is increasingly used to support temporary power supplies.
The new chapter sets out requirements for the safe installation of battery systems, including protections against thermal runaway, adequate ventilation, disconnection arrangements, and the interface between battery systems and other parts of the installation. For builders involved in projects incorporating solar PV with battery storage, or sites using battery-powered distribution systems, this chapter introduces specific duties that did not previously exist in a consolidated form within the Wiring Regulations.
What this means in practice: If you are installing or commissioning any battery energy storage system as part of a building project, your electrician must now work to the requirements of this new chapter. Principal contractors should ensure that any specialist subcontractors engaged for BESS work are working to the 2026 amendment.
2. Major Revisions to Medical Locations (Section 710)
Section 710, which covers electrical installations in medical locations, has been significantly revised. Medical locations are now formally classified into three groups:
- Group 0: Areas where no applied parts are used (waiting rooms, corridors)
- Group 1: Areas where applied parts are used but interruption of supply is not life-threatening
- Group 2: Areas such as operating theatres and intensive care units, where interruption of supply could be life-threatening
For Group 2 areas, the revised standard requires medical IT systems incorporating a transformer and insulation monitoring device. These systems are designed to maintain supply during a first electrical fault and alert staff before any disconnection occurs. Two independent power supplies and an uninterruptible power supply (UPS) must also be provided, positioned as close as possible to the equipment they support.
What this means in practice: Builders and M&E contractors working on healthcare construction or fit-out projects must ensure their designs and installations meet the new Group classifications. This is particularly relevant for hospital ward refurbishments, new healthcare facilities, and dental surgery fit-outs.
3. Power over Ethernet (PoE) — Section 716 Updated
Section 716, covering Safety Extra Low Voltage (SELV) and Protective Extra Low Voltage (PELV) systems, has been updated to include specific provisions for Power over Ethernet (PoE) connections. PoE is increasingly used across commercial and public buildings to power devices such as access control systems, IP cameras, VoIP phones, and smart building sensors — all areas relevant to modern construction projects.
The amendment specifies that PoE electrical connections must comply with BS ISO/IEC 11801-1 and must be capable of supporting a continuous operating current of 750 mA per contact.
What this means in practice: Where PoE systems are being installed as part of a building’s fixed infrastructure — for example, in a school, office, or hospital project — the installation must now meet these updated technical requirements. Data cabling and M&E teams need to be aware of the additional electrical duties that apply.
4. Incorporation of Amendment 3 (2024)
Amendment 4 formally incorporates the content of Amendment 3:2024 into the main body of the document. This means the current version is now designated BS 7671:2018+A4:2026 and represents a consolidated update. Professionals working from earlier printed copies should be aware that the standard has evolved considerably from the original 2018 edition.
5. Continued Alignment with CENELEC and IEC Standards
Amendment 4 continues the process of aligning BS 7671 with European (CENELEC) and international (IEC) standards. This is relevant for contractors working on cross-border projects or supplying products that require CE or UKCA marking. It also means that for certain technical requirements, reference to the underlying international standard may be needed for full context.
What Is the Transition Period?
The previous version of the standard — BS 7671:2018+A2:2022+A3:2024 — will be formally withdrawn six months from the April 2026 publication date. This means electrical work specified, designed, or contracted after that withdrawal date should comply with Amendment 4.
During the transition period, work already underway or designed prior to the withdrawal date will generally be assessed against the version current at the time of design. However, any new projects should begin the process of working to Amendment 4 immediately to avoid having to revise designs and specifications later.
What Builders and Site Managers Need to Do Now
Review your existing specifications. If you are mid-project on a healthcare, commercial, or residential scheme incorporating battery storage or PoE systems, discuss with your M&E engineer or electrical contractor whether the Amendment 4 requirements affect your design.
Update procurement and subcontractor requirements. When engaging electrical subcontractors, ensure your contracts reference compliance with BS 7671:2018+A4:2026. This protects you legally and ensures the work is carried out to the current standard.
Brief your site supervisors. While the detailed technical requirements of Amendment 4 sit with your electrical teams, site supervisors and principal contractors benefit from understanding what has changed — particularly around battery storage systems, which present new hazards on site during installation and commissioning.
Check your temporary electrical installation. Construction site temporary installations must comply with BS 7671, including Part 7 provisions for construction sites specifically. While Amendment 4 may not dramatically alter your site setup in most cases, it is good practice to confirm with your electrical contractor that your temporary installation is assessed against the current edition.
Training and CPD. Electrical professionals — including those working in construction — are expected to keep their knowledge current. If your electrical team have not yet studied the Amendment 4 changes, the IET offers guidance and training packages alongside the published standard.
Where to Get the Current Standard
BS 7671:2018+A4:2026 is available for purchase directly from the IET at theiet.org. The standard is not free to download, but the IET does publish supplementary guidance documents and the Wiring Regulations 18th Edition Guidance Notes series which many electricians find useful alongside the core standard.
The HSE’s guidance on electrical safety in construction (HSG141) provides practical interpretation of the legal requirements for site-based electrical work, and is a useful companion document for site managers who need to understand the regulatory context without working through the technical detail of BS 7671 itself.
Summary
Amendment 4 (2026) to BS 7671 represents the most significant update to the UK’s electrical installation standard in several years. The key changes — a new chapter on stationary secondary batteries, revised classifications for medical locations, and updated PoE provisions — reflect the rapid evolution of technology in modern construction.
For builders and electrical contractors, the practical implications are clear: new projects must be designed and built to the updated standard, subcontractor requirements should be updated accordingly, and electrical professionals must invest time in understanding what has changed.
As construction sites become increasingly complex electrical environments — with battery storage, EV charging infrastructure, smart building systems, and temporary high-capacity power supplies all present simultaneously — staying current with BS 7671 is not just a compliance matter. It is a fundamental part of keeping workers and future building users safe.
Internal Links of Interest https://buildersafety.org/risk-assessment-for-general-electrical-work/
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