BS 7671 Amendment 4: What Solar and Battery EPCs Must Do

Quick Answer

BS 7671 Amendment 4 at a Glance

BS 7671, the IET Wiring Regulations, is the UK national standard for low voltage electrical installations. The IET says Amendment 4 becomes the standard for all new low voltage installations, additions and alterations to existing installations, and periodic inspection and testing. It also folds Amendment 3 into the main document, so it replaces the separate PDF that went with the earlier book. For a solar or battery EPC, the date that matters is 15 October 2026.

What Is New for Solar and Battery Work

The IET's list of significant changes is short. One item bears directly on storage work.

What the public sources do not show is clause-level detail. The standard is paid, and the IET and NICEIC publish what changed, not the text. Read the new chapter in your own copy before you design or price a storage job after 15 October.

Which Edition Applies to Which Job

NICEIC attaches conditions to finishing an earlier design to the previous standard. It recommends telling the client the design follows a withdrawn standard. It also advises checking whether the contract requires the "latest" BS 7671, and whether insurers or licensing authorities specify the latest standard. If Amendment 4 affects the design, work out whether it adds cost and settle that with the client before work continues.

Certificates, Forms and Declarations

The IET publishes the model forms for BS 7671:2018+A4:2026 as free PDFs.

Battery Circuits and AFDDs

Arc fault detection devices are a common worry on storage jobs. NICEIC states that BS 7671 requires AFDDs only on socket-outlet circuits rated up to 32 A in four building types: care homes, high rise residential buildings, houses in multiple occupation and purpose-built student accommodation. It also says there is no requirement in BS 7671 to fit AFDDs within a circuit that supplies battery energy storage systems. That is NICEIC's answer in its FAQ, so check it against your copy of the standard before leaving an AFDD out of a design.

What EPC Teams Should Do Now

Where Design Software Fits

An edition change shows up in design documents: single-line diagrams, schedules and bills of materials. Design software like Reslink produces those from one 3D design, so a design revised for Amendment 4 updates across the documents instead of being redrawn. It does not decide whether a design meets BS 7671. A competent electrician has to check the design against the standard.

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Frequently Asked Questions

Q1. Who has to hold a copy of Amendment 4?

NICEIC says certified businesses must demonstrate access to Amendment 4 from 15 October 2026 to keep their certification. Before that date, firms working only to the previous edition do not need to show a copy. NICEIC also notes that single downloadable PDFs of BS 7671 are not legally available. A digital version is sold under an annual licence.

Q2. What else changed apart from batteries?

The IET lists a new section on functional earthing for ICT equipment, a new section on Power over Ethernet, and a major revision of Section 710 Medical Locations with a new test results schedule. It adds that further changes run through all parts of the standard, so its list of significant changes is not exhaustive.

Q3. Does Amendment 3 still matter after 15 October?

Not as a separate document. Amendment 3 is incorporated into the main text of Amendment 4. Until 15 October 2026, the IET says the earlier book, Amendment 2 and the free Amendment 3 PDF remain valid together.

Q4. Does Amendment 4 change anything for plug-in solar?

The IET's list of significant changes does not mention plug-in solar. The plug-in framework runs through SI 2026/848 and the interim product specification, covered in our UK plug-in solar guide. Check the standard's text if a plug-in job involves fixed wiring.

Q5. Where can I get the model forms and the full text?

The IET publishes free PDFs of the model forms for BS 7671:2018+A4:2026. The full standard is sold by the IET and trusted resellers. The IET warns about counterfeit copies and advises buying from its bookshop or its listed resellers.

Final takeaway

Amendment 4 has been usable since April, so the 15 October cutover is administrative for jobs designed earlier and binding for every new design after it. The part to read in full is the new storage chapter. The IET and NICEIC confirm that it exists and what it covers, but not what it requires.

Use the days around the cutover to sort live designs by date, check contracts and insurer wording, and make sure every estimator and electrician has a copy.

You May Also Like

• UK Plug-In Solar 2026: What EPCs Should Tell Clients
• NFCC BESS Guidance 2026: What's Confirmed, What's Open for UK EPCs
• MCS 2027 Deadline: What's Actually Changing for Solar and Battery EPCs

Sources

• IET and BSI, "IET and BSI publish Amendment 4 (2026) to BS 7671:2018", press release, 15 January 2026
• IET Electrical, "Ensure you are up to date with BS 7671"
• NICEIC, "Understanding BS 7671:2018 + Amendment 4:2026" (FAQs on transition, forms, EICRs, AFDDs and access)

This guide summarises published IET and NICEIC guidance and is not a substitute for BS 7671:2018+A4:2026 or advice from a competent electrician. Check the current text before design or certification.