BS 7671 Amendment 4 (A4:2026)
What changed in the new wiring regs — for working sparkies
Published: 15 April 2026 by the IET and BSI (the "Orange Book").
Old version withdrawn: 15 October 2026.
What that means: any new electrical installation work designed, installed or verified after 15 October 2026 must comply with A4. Work already in progress against A2:2022+A3:2024 before that date can finish under the old version.
WireWrite is already on A4:2026
Every UK certificate type — EIC, Minor Works, and EICR — defaults the BS 7671 amendment field to A4:2026. The PDF prints the amendment number on the cover and again next to each "Departures from BS 7671" entry.
You can still pick A3:2024, A2:2022, A1:2020 or "None" from the dropdown when you're documenting work that was carried out under an older version, or when you're doing periodic inspection (EICR) of an installation that was originally certified under an earlier amendment.
No action required from you — just create a new certificate. The default already changed.
What's new in A4 vs A2:2022 + A3:2024
Chapter 57 — stationary secondary batteries (BESS)
Brand new. Covers domestic battery storage, commercial BESS and industrial-scale lithium installations. Adds requirements around:
- Thermal runaway prevention and detection
- Means of isolation for maintenance
- Location restrictions (escape routes, ventilation, fire compartmentation)
- Documentation and commissioning evidence
First time BS 7671 has had dedicated battery storage regulations. Previously Section 712 (PV) and manufacturer instructions were the only references.
Revised earthing for EV chargers
Section 722 (electric vehicle charging installations) updated. PME-derived earthing arrangements get tighter rules around open-PEN protection and the use of earth electrodes / RCDs. If you're installing EV chargers, this is the change you'll feel most often on a job.
What hasn't changed
For a typical domestic or light commercial installation, A4 is mostly business-as-usual:
- Voltage drop limits (3% lighting / 5% other) — unchanged. Table 4Ab is the same.
- Cable current-carrying capacity tables (4D5, 4D4A, 4D4B etc.) — unchanged.
- Maximum Zs values in Tables 41.3 / 41.4 — unchanged.
- Ring final permission under Reg 433.1.204 — unchanged.
- The EIC / Minor Works / EICR forms in Appendix 6 — same layout, same fields, just amendment number bumped.
Things to put on your A4 checklist
- 1.Get hold of the Orange Book — IET Bookshop sells the consolidated edition in print and PDF. Don't try to work from A2 + A3 + A4 PDFs side by side.
- 2.Check your Competent Person Scheme's CPD requirement — most of NICEIC, NAPIT, ELECSA and STROMA expect members to do A4 update training before October 2026.
- 3.If you do EV chargers — read Section 722 carefully. The open-PEN handling has shifted again.
- 4.If you're installing or commissioning battery storage, Chapter 57 is brand new territory. Manufacturer guidance plus the IET Code of Practice for Electrical Energy Storage Systems (3rd edition) are still your primary references; A4 sets the regulatory framework around them.
- 5.For new EICs after 15 October 2026, leave the WireWrite amendment dropdown on the default A4:2026.
Doing an EICR after October?
Periodic inspection assesses an existing installation against the regulations in force when it was installed, not against the current amendment. Pick the amendment that matches the original installation date — A1:2020 / A2:2022 / A3:2024 / A4:2026 — from the WireWrite dropdown when you're filling in Section A.
Findings that would not have been compliant under the original amendment are coded as observations (C1 / C2 / C3 / FI) on the EICR — you don't fail an installation just because it doesn't meet today's standards.
BS 7671:2018+A4:2026 calculators
Every WireWrite calculator is updated for A4:2026 and verified against the published tables in the IET Wiring Regulations.
Cable Size Calculator
BS 7671 Appendix 4 with Ca/Cg/Ci derating factors
Earth Fault Loop Impedance
Zs check against Table 41.3 / 41.4 with Cmin = 0.95
Voltage Drop
3% lighting / 5% other per Table 4Ab
Circuit Check
IB ≤ IN ≤ IZ verification per Reg 433.1.1
Maximum Demand
IET OSG Appendix A Table A2 (Households)
Solar String
1000 V DC limit per BS 7671 Section 712
Frequently asked questions
When does BS 7671 Amendment 4 become mandatory?
A4:2026 was published on 15 April 2026. The previous version (A2:2022+A3:2024) is withdrawn on 15 October 2026. From that date, all new electrical work in the UK must comply with A4.
Does WireWrite already issue A4-compliant certificates?
Yes. The amendment field on every UK certificate (EIC, Minor Works, EICR) defaults to A4:2026. The PDF stamps the amendment number on the cover. You can still pick A3:2024 / A2:2022 / A1:2020 / None from the dropdown for legacy retests.
What is Chapter 57?
Chapter 57 is brand new in A4:2026. It covers stationary secondary batteries — domestic, commercial and industrial battery energy storage systems (BESS). It sets requirements around thermal runaway, isolation during maintenance, location restrictions and documentation. This is the first time BS 7671 has had dedicated regulations for battery storage.
Have voltage drop limits changed in A4?
No. The 3% lighting / 5% other limits in Table 4Ab remain unchanged. WireWrite's Voltage Drop and Cable Sizer calculators use these values.
Do I need to buy the new Orange Book to do A4 work?
You should have access to BS 7671:2018+A4:2026 in some form — the Orange Book is the consolidated edition (replacing the Brown Book + A3:2024 PDF bolt-on). The IET and BSI sell hard-copy and PDF licences. WireWrite is not a substitute for the standard itself.