BS 7671 Amendment 4:2026 — The Complete Technical Guide

1. What is Amendment 4 and why does it matter?

BS 7671 — the Requirements for Electrical Installations — is the UK national standard jointly maintained by the IET and BSI. It is the primary way the industry demonstrates compliance with the Electricity at Work Regulations 1989. Amendment 4 is the fourth update to the 18th Edition since its original publication in 2018, and it is issued as a second full consolidated edition — known in the industry as the Orange Book — absorbing all previous amendments (A1, A2, A3) into a single document.

This is not a minor correction. Amendment 4 introduces completely new chapters and sections that did not exist before, reflecting just how rapidly the electrical landscape has changed since 2022. Battery energy storage, Power over Ethernet, and smart ICT infrastructure have all moved from niche applications to everyday installations — and the regulations are now catching up.

2. Chapter 57 — Stationary Secondary Battery Installations

This is the headline change. Chapter 57 is the first dedicated chapter for battery energy storage systems (BESS) in BS 7671. Until now, there was no specific regulatory framework — designers and installers had to rely on PAS 63100, manufacturer instructions, and best practice guidance. That gap is now formally closed.

What does Chapter 57 cover?

The chapter applies to permanently installed secondary battery systems where the primary purpose is electrical energy storage and supply. This covers domestic battery storage (typically paired with solar PV), commercial BESS, and grid-connected battery arrays, including vehicle-to-home (V2H) and vehicle-to-grid (V2G) configurations.

It does not apply to batteries within pluggable UPS units, fire safety systems (BS 5839), emergency lighting systems (BS 5266), or central safety power supply systems.

Protective devices for bidirectional energy flow

One of the most practically important requirements is that all protective devices must be suitable for two-way energy flow. This rules out many conventional unidirectional overcurrent devices that have been routinely applied to battery-backed circuits. Regulation 551.7.1 has been redrafted to require a suitable protective device wherever bidirectional flow is possible, and there is a new prohibition on connecting a source to the load side of an RCD under certain conditions.

Stationary batteries are now formally classified as generating sets under Regulation 551.7.2.1, not loads. The previous Regulation Group 551.8 has been deleted and its content migrated into Chapter 57.

Location, ventilation, and fire risk

The chapter is detailed on where battery systems can and cannot be sited:

• Thermal runaway — fire risk mitigation measures must be appropriate to the battery chemistry. Lithium-ion and lead-acid present very different profiles.
• Ventilation — adequate ventilation must be demonstrated, particularly for lead-acid systems which can produce hydrogen.
• Escape routes — batteries must not be located where a fire would compromise means of escape. Loft installations common in legacy retrofits may now need revisiting.
• Isolation — dedicated isolation procedures during maintenance and testing are required. Unlike a conventional supply, a BESS is a continuous energy source that cannot simply be switched off at the meter.

3. Section 716 — Power over Ethernet (PoE)

Power over Ethernet has become a mainstream delivery mechanism for LED lighting drivers, IP cameras, access control, BMS sensors, and small appliances in commercial buildings. Despite widespread deployment, BS 7671 had no specific framework for PoE installations. Section 716 addresses this directly.

The voltage limits — read carefully

Standard BS 7671 SELV and PELV limits are 50 V AC and 120 V DC. Part 7 special location sections can modify these, and Section 716 does so significantly:

The 60 V limit in dry locations accommodates PoE++ (IEEE 802.3bt Type 4) which can deliver up to 90 W per port. The 15 V limit elsewhere reflects the increased hazard from DC in damp environments.

Cable and connector requirements

All 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. This is a specific and testable requirement. Key practical implications:

• Where existing telecoms cabling is repurposed for PoE, it must be assessed for suitability — conductor CSA, connector ratings, and patch panel terminal ratings all need checking
• Power sourcing equipment (PoE switches and injectors) must comply with BS EN 62368-3
• PoE systems must be tested for both data performance and electrical safety compliance

4. Section 545 — Functional Earthing for ICT Systems

Modern ICT infrastructure requires both protective earthing (for shock protection) and functional earthing (for signal integrity and EMC compliance). Until Amendment 4, there was no dedicated BS 7671 provision for functional earthing, creating uncertainty particularly around separate earth electrodes for IT equipment and the interaction between FE and PE conductors.

The core principle

What Section 545 introduces

• Minimum conductor CSA for functional bonding conductors
• Identification requirements — FE conductors must be clearly distinguishable from PE conductors
• Main functional earthing terminal (MFET) — the ICT equivalent of the main earthing terminal
• Equipotential bonding ring conductors — for data centres and broadcast environments requiring a consistent reference potential
• Combined PE/FE conductors — permitted, but with specific requirements on CSA and identification

This section is directly relevant to school, hospital, commercial, and industrial installations where structured cabling and server infrastructure co-exist with conventional electrical systems.

5. Section 710 — Medical Locations

Section 710 has been completely overhauled to align with IEC 60364-7-710:2021 and its CENELEC adoption. This is the most substantive revision of any existing section in Amendment 4.

Revised group classification

Group 2 requirements

Group 2 locations attract the most demanding requirements under the revised section:

• Medical IT systems — a transformer and insulation monitoring device (IMD) must be installed to maintain supply during a first fault. The IMD alerts staff before disconnection on a second fault, maintaining the principle that a Group 2 supply must never fail silently.
• Two independent supplies — mandatory for Group 2 to eliminate single-point failure
• UPS — must be provided and positioned as close as possible to the equipment it supports, minimising the length of potentially vulnerable cabling
• Supplementary bonding test schedule — a new requirement to record resistance measurements of supplementary protective equipotential bonding conductors; this must be included in all commissioning and periodic inspection documentation

6. Other Notable Changes

Chapter 81 — Energy Efficiency (new, introductory)

Chapter 81 introduces a framework for energy efficiency in LV installations, aligned with the UK’s net-zero trajectory. At this stage it is advisory — following Appendix 17 guidance on power factor correction and circuit layout is not mandatory. However, this signals clear direction of travel, and the expectation is that future editions will strengthen these provisions as the regulatory landscape around building energy performance evolves.

Regulation 521.5.1 — Ferromagnetic enclosures

A clarifying note has been added: for switchgear and controlgear assemblies complying with BS EN IEC 61439, conductors carrying up to 200 A may pass through separate apertures in ferromagnetic enclosures. Above 200 A through separate holes, a temperature-rise test must confirm safe operation.

Regulation 521.10.202 — Cable support in fire conditions

A new note clarifies that the intent of this regulation is to prevent hanging or collapsed cables from blocking escape routes or impeding firefighting — it is not a requirement for circuit integrity of general wiring. Fire survival requirements remain in Chapter 56, BS 5839, BS 5266, and BS 8519.

Section 537 — Firefighter’s switches

Regulation 537.4.2 now requires firefighter’s switches to be located in positions identified by the fire engineer as part of the building’s fire strategy. This formalises the requirement for collaboration between electrical designers and fire engineers. Regulation 537.4.2.1 has been deleted.

Section 551 — Low-voltage generating sets

Significant revisions reflect the reality of bidirectional energy systems. Regulation 551.7.1 has been redrafted with a new requirement for suitable protective devices in bidirectional flow scenarios, and a prohibition on connecting a source to the load side of an RCD under certain conditions. Regulation 551.7.2 has been split into two separate regulations.

Chapter 65 — EICR documentation

• EICRs must now include recipient guidance based on the Appendix 6 model
• Photographic and thermographic images may be appended as supporting evidence — now formally acknowledged in the regulations
• Signatures must be from those conducting the inspection and authorising the report
• Important: issuing a Further Investigation (FI) code does not automatically result in an Unsatisfactory outcome — overall condition must be assessed on its merits

Appendix updates — cable rating data

New current-carrying capacity data has been added for buried cables installed in ducts, enabling more accurate volt drop and cable sizing calculations rather than relying on conservative assumptions.

7. Qualifications and Competency

If you already hold the 18th Edition qualification, a focused one-day Amendment 4 update course is the accepted route — no need to resit the full exam. Training providers will be under pressure from late summer as the October deadline approaches. Book early.

8. Key Dates at a Glance

Frequently Asked Questions