BS 7671 Amendment 4 was published on 15 April 2026, and the previous version is withdrawn on 15 October 2026, from which point new work is designed to it. It widens 30mA RCD protection to AC lighting circuits in dwellings, broadens where arc fault detection devices are recommended, pushes surge protection into more homes, and introduces Chapter 57 covering solar, battery storage, and bidirectional EV charging. Existing installations do not need retrospective upgrading.
Key takeaways
- Published 15 April 2026 and usable straight away. The superseded version is withdrawn on 15 October 2026.
- 30mA RCD protection now extends to AC lighting circuits in dwellings, closing the last gap left by Amendment 2.
- New Chapter 57 governs solar PV, battery storage, and bidirectional EV chargers as one coherent ruleset.
- Nothing is retrospective. Your existing installation does not become non-compliant on 15 October 2026.
- A missing AFDD produces a C3 observation on an EICR, which is advisory and does not fail the report.
Every few years the IET publishes an update to the UK Wiring Regulations, BS 7671. The current version is the 18th Edition, published in 2018. Amendment 4 to that edition was published on 15 April 2026 and can be used straight away. The superseded version, BS 7671:2018+A2:2022+A3:2024, is withdrawn on 15 October 2026, so from that point new work is designed to Amendment 4.
Most homeowners never read a wiring regulation, and rightly so. What matters is what changes on your invoice, on your consumer unit label, and on the paperwork you get when the electrician leaves. Here is the short version, in plain English.
What is BS 7671 Amendment 4?
Amendment 4 widens the safety envelope in three main directions: more circuits get 30 mA RCD protection, more circuits get arc fault protection (AFDDs), and homes with batteries or solar have a proper set of rules for the first time (the new Chapter 57 on prosumer installations). Surge protection (SPDs) becomes standard on more residential installs, and the treatment of Power over Ethernet (PoE) gets tidied up.
None of it makes older installations illegal. What it does mean is that any new design, any consumer unit change, and any rewire from October 2026 will be built to the widened rules.
What changed for RCD protection on lighting?
Amendment 2 (2022) already required 30 mA RCD protection on nearly every final circuit. Amendment 4 closes the last gap: AC lighting circuits in dwellings now also fall in scope.
What this means for you: if you’re having a consumer unit change or a partial rewire, expect an RCBO on the lighting circuits (an RCBO is a single device that combines the overload protection of an MCB with the earth-leakage protection of an RCD). Most modern consumer units are already built this way, so the change is invisible on many jobs.
Are AFDDs now required in homes?
An AFDD listens for the electrical signature of an arcing fault, the sort that starts fires in loft spaces and behind sockets. Amendment 4 broadens where AFDDs are recommended in dwellings.
In practice, an AFDD costs roughly 3 to 4 times what a standard RCBO does, so this line item is visible on an estimate. You are entitled to ask your electrician which circuits carry AFDDs on your job and why, and to opt for more coverage than the minimum if you want to.
Do you need a surge protection device?
An SPD protects the wiring and connected appliances from voltage transients, typically caused by a nearby lightning strike or a switching event on the network. Amendment 4 pushes SPDs into more residential installs by default.
A whole-home SPD sits inside the consumer unit and adds around £100 to £250 to a consumer unit change, depending on the device and how the board is arranged. SPDs also have a service life of roughly 10 years, so they get replaced on a rolling basis at each EICR or CU refresh.
What does Chapter 57 cover for solar and battery?
Amendment 4 introduces a dedicated chapter for “prosumer” installations, which is the technical name for homes that both consume and generate electricity. This covers:
- Solar PV
- Stationary battery storage
- Bidirectional EV chargers (V2H, V2G)
- Backup generators
The chapter formalises how these systems interact with the grid connection, when they can and cannot island (run in isolation from the grid during a power cut), and what protection they must have. If you are having a solar-plus-battery install or considering a V2G charger, this is the ruleset your installer works to. See our EV chargepoint grants post for the grant landscape, and our EV charger installation page for our own service.
What changed for Power over Ethernet?
Home cabling for smart home devices, IP cameras, and access points is often powered over the same Cat6 cable that carries the data. Amendment 4 updates the guidance on cable ratings and installation methods for PoE to reflect the higher currents modern PoE++ standards can deliver.
Only relevant if you’re planning structured cabling for a self-build or a major refurbishment. If your home has one wireless router in the hallway and that’s it, nothing changes for you.
What else changed in Amendment 4?
- Updated cable colour and marking rules for prosumer installations
- Tightened guidance on external influences (temperature, moisture, mechanical stress) for outbuilding and garden circuits
- Clearer language on labelling and documentation for the “as-fitted” record
When does Amendment 4 come into force?
Three dates to know:
- 15 April 2026: Amendment 4 published
- 15 October 2026: the superseded version is withdrawn. From this point any new installation, consumer unit change, or rewire is designed and certified to A4.
- Existing installations: no requirement to bring them up to A4 retrospectively. Your EICR is still assessed against the standard your installation was designed to, with C3 “improvement recommended” observations for anything that would fail the current rules.
| Change | What it affects | Typical added cost |
|---|---|---|
| RCD on lighting circuits | New consumer units, rewires | Usually none, RCBO boards are already standard |
| Wider AFDD recommendation | New designs, some rewires | 3 to 4x an RCBO per protected circuit |
| Surge protection (SPD) | Consumer unit changes | £100 to £250 per board |
| Chapter 57 (prosumer) | Solar, battery, V2G installs | Design overhead, not a fixed cost |
| PoE cable ratings | Structured cabling, self-builds | Specification only |
Cost guidance as of July 2026 and indicative only. The superseded version is withdrawn on 15 October 2026. Amendment 4 is not retrospective.
Will Amendment 4 make your EICR harder to pass?
Not automatically. C1 and C2 observations, the ones that produce an Unsatisfactory result, are about danger. A missing AFDD does not create a C1 or C2; it produces a C3 “improvement recommended”, which does not fail the report. See our EICR cost guide for the full observation code breakdown.
What may change is the shape of the remedial estimate you get after an Unsatisfactory EICR. If your installation is being brought forward to modern standards anyway, your electrician will spec Amendment 4-compliant kit as the default. You always get to choose the level of upgrade you want.
What should you ask your electrician?
When you next get an estimate for a consumer unit change or rewire in Wiltshire, three good questions:
- Is this estimate designed to Amendment 4 or Amendment 3?
- Which circuits carry AFDDs, and can I opt for more coverage?
- Is an SPD included, and if so which type?
Any NICEIC or ECA approved contractor will answer all three without hesitation. Every job we estimate from October 2026 onwards is designed to A4 by default, with any deviation clearly flagged and priced.
Get an estimate
See our house rewire page or EICR testing page for our own domestic services, or contact us for an estimate on your property.
Service areas: Nulectrics is based in Chippenham, Wiltshire. We cover domestic work across Chippenham, Corsham, Calne, Melksham, Devizes, Trowbridge, Bath and the surrounding area, and commercial work UK-Nationwide.