The complete guide to BS 7671:2018+A4:2026 — the 18th Edition of the IET Wiring Regulations. Every part of the standard explained, what each of the four amendments actually changed, and the A4:2026 additions: Chapter 57 for stationary secondary batteries, Section 716 for Power over Ethernet, Section 545 for ICT functional earthing, Chapter 81 for energy efficiency, and the redrafted Regulation 551.7.1 for bidirectional energy flow.
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Written and reviewed by Andrew Moore, founder of Elec-Mate, against BS 7671:2018+A4:2026, IET Guidance Note 3 and the IET On-Site Guide.
The short answer
BS 7671:2018+A4:2026 — the 18th Edition of the IET Wiring Regulations as amended by A1:2020, A2:2022, A3:2024 and A4:2026. Amendment 4 was issued on 15 April 2026 and may be implemented immediately; the previous version is withdrawn on 15 October 2026. BS 7671 is not statutory in itself, but compliance is the accepted way to satisfy the Electricity at Work Regulations 1989 and Part P of the Building Regulations.
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01 · BS 7671 Hub
BS 7671 is the British Standard that sets out the requirements for the design, erection, and verification of electrical installations in the United Kingdom. Published jointly by the British Standards Institution (BSI) and the Institution of Engineering and Technology (IET), it is the single most important document for every working electrician in the UK. The current version is BS 7671:2018+A4:2026 — the 18th Edition, as amended by A1:2020, A2:2022, A3:2024 and A4:2026.
| Question | Answer |
|---|---|
| Current version | BS 7671:2018+A4:2026 |
| Amendment 4 issued | 15 April 2026 — may be implemented immediately |
| Previous version withdrawn | 15 October 2026 (A2:2022 + Corrigendum May 2023 + A3:2024) |
| 18th Edition issued | 1 July 2018; in effect for designs after 31 December 2018 |
| Voltage scope | Up to and including 1000 V AC or 1500 V DC |
| Structure | Parts 1 to 7, plus Part 8 (functional requirements) |
| Legal status | Not law itself — the accepted route to satisfying the Electricity at Work Regulations 1989 and Part P |
The standard applies to circuits supplied at nominal voltages up to and including 1000 V AC or 1500 V DC. That covers virtually every domestic, commercial, and light industrial installation in the country — from a single socket-outlet in a flat to a complete rewire of a hospital. It does not cover certain specialist installations such as mines, quarries, explosive atmospheres, or high-voltage distribution systems, which are covered by separate regulations.
BS 7671 is not a textbook or a how-to guide. It is a set of requirements — minimum standards that must be met for an installation to be considered safe. The companion documents — the IET Guidance Notes (GN1 through GN8), the On-Site Guide, and the Electrician's Guide — provide the practical interpretation and worked examples that help electricians apply the regulations on site. The most commonly referenced companion is Guidance Note 3 (GN3): Inspection and Testing, now in its 9th Edition.
| Amendment | Issued | Headline changes |
|---|---|---|
| A1:2020 | February 2020 (electronic) | Section 722 (EV charging) amended and rebased on HD 60364-7-722:2018 |
| A2:2022 | 28 March 2022 (brown cover) | AFDDs became a requirement in four premises types (421.1.7); new Chapter 82 (prosumer's installations); 443.5 risk-assessment method deleted; Appendix 3 Table 3A deleted and RCD testing changed |
| A3:2024 | 31 July 2024 (electronic) | Two new definitions and one new regulation on bidirectional and unidirectional devices (530.3.201) |
| A4:2026 | 15 April 2026 (orange cover) | New Chapter 57 (stationary secondary batteries), new Section 716 (Power over Ethernet), new Section 545 (functional earthing for ICT), new Chapter 81 (energy efficiency); 551.7.1 redrafted for bidirectional energy flow |
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Every key change in the 2026 amendment on one page. AFDDs, TN-C-S protection, new schedule columns, model forms. Pinned on your van dash.
02 · BS 7671 Hub
BS 7671 is built from seven numbered parts covering design and installation, plus Part 8, which carries the functional requirements added by later amendments. Knowing the structure is what makes the book quick to use — whether you are looking up a regulation, studying for the 2382 exam, or checking compliance on site.
Defines the scope of the standard — what types of installations it covers and what it does not. Sets out the fundamental principles of electrical safety: protection against electric shock, protection against thermal effects, protection against overcurrent, protection against fault current, and protection against overvoltage. Regulation 133.1.3 also sits here: where equipment is not to an applicable standard, or is used outside the scope of its standard, the designer must confirm it gives at least the same degree of safety and record it as a departure on the Part 6 certification.
Contains all the defined terms used throughout the standard. Understanding these definitions is critical because many terms have specific technical meanings that differ from everyday usage. For example, "extraneous-conductive-part" has a precise definition that determines whether bonding is required. "Skilled person," "instructed person," and "ordinary person" have specific meanings that affect the level of protection required. Part 2 is frequently tested in the 2382 exam.
Requires the designer to assess the characteristics of the installation before starting the design: the purpose of the installation, the supply characteristics (earthing system, supply voltage, prospective fault current), the nature of the demand, the environmental conditions, and compatibility with other systems. You cannot size cables, select protective devices, or design earthing arrangements without first assessing the general characteristics. A4:2026 added a protective neutral bonding (PNB) figure and requirements to Regulation 312.2.1.1.
The largest and most frequently referenced part. Covers protection against electric shock (Chapter 41), protection against thermal effects (Chapter 42), protection against overcurrent (Chapter 43), protection against voltage disturbances and electromagnetic disturbances (Chapter 44), and isolation and switching (Chapter 46). Chapter 41 holds the automatic disconnection of supply (ADS) requirements — Table 41.1 maximum disconnection times and Tables 41.2 to 41.6 for maximum earth fault loop impedance — which are the tables electricians reach for most often on site.
Covers the practical selection and installation of equipment — wiring systems (Chapter 52), protection, isolation, switching, control and monitoring (Chapter 53), earthing arrangements and protective conductors (Chapter 54), other equipment (Chapter 55), safety services (Chapter 56) and, new at A4:2026, stationary secondary batteries (Chapter 57). This is where you find cable selection, installation methods, minimum conductor sizes, and equipment ratings. Regulation 530.3.201 on unidirectional and bidirectional protective devices sits here, as does the redrafted Regulation 551.7.1 for generating sets in parallel with another source.
Sets out the requirements for initial verification (Chapter 64) and periodic inspection and testing (Chapter 65). It specifies which tests must be carried out and what the pass criteria are. Table 64 — minimum values of insulation resistance and the DC test voltages, applied by Regulation 643.3.2 — is in this part. The maximum earth fault loop impedance tables are not: they are Tables 41.2 to 41.6 in Chapter 41, with the supporting loop-impedance material in Appendix 3. Part 6 is the basis for every electrical certificate issued in the UK.
Contains additional or modified requirements where the risk of electric shock or fire is increased. Sections include locations containing a bath or shower (701), swimming pools and other basins (702), saunas (703), construction and demolition sites (704), agricultural and horticultural premises (705), conducting locations with restricted movement (706), marinas (709), exhibitions, shows and stands (711), solar PV (712), Power over Ethernet (716, new at A4:2026), and EV charging (722). Where a Part 7 section applies, its requirements supplement or modify the general requirements in Parts 1 to 6 and Part 8. Part 7 is heavily tested in the 2382 exam because it is full of specific, memorable requirements.
Part 8 did not exist in the 2018 book — energy efficiency was informative guidance in Appendix 17. Amendment 2:2022 added Chapter 82, Prosumer's low-voltage electrical installations, which sets requirements for installations with local generation and storage (Sections 821 to 826). Amendment 4:2026 added Chapter 81, an informative chapter on energy efficiency that points the reader to the Building Regulations and to BS HD 60364-8-1:2019, and deleted Appendix 17.
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Elec-Mate's 18th Edition course works through the whole standard with questions mapped to the City and Guilds 2382-22 exam syllabus.
03 · BS 7671 Hub
BS 7671:2018 was issued on 1 July 2018 and came into effect on 1 January 2019, replacing the 17th Edition (BS 7671:2008+A3:2015). Installations designed after 31 December 2018 are to comply with the 18th Edition, so the overlap was six months rather than a year. These are the 2018 changes that still shape day-to-day practice.
Regulation 411.3.4, "Additional requirements for circuits with luminaires", states: within domestic (household) premises, additional protection by an RCD with a rated residual operating current not exceeding 30 mA shall be provided for AC final circuits supplying luminaires. It uses "shall", so it is a requirement, not a recommendation — and it has been in force since the 18th Edition was published in 2018. It is often reported as a new Amendment 4 rule; it is not. On new work and rewires, lighting circuits are protected by a 30 mA RCD or RCBO.
This is the most widely misquoted regulation in the book, in both directions. The 18th Edition introduced 421.1.7 in 2018 as a recommendation. Amendment 2:2022 redrafted it into a requirement for four premises types, and Amendment 4:2026 reworded the first of them. As it now stands, AFDDs conforming to BS EN 62606 shall be provided for single-phase AC final circuits supplying socket-outlets with a rated current not exceeding 32 A in (a) high rise residential buildings (HRRBs), (b) houses in multiple occupation (HMOs), (c) purpose-built student accommodation, and (d) care homes. A note assumes an HRRB to be a residential building over 18 m in height or in excess of six storeys, whichever is met first. For all other premises, AFDDs are recommended for single-phase AC final circuits supplying socket-outlets not exceeding 32 A. Where used, they go at the origin of the circuit to be protected, and Regulation 532.6 confirms they are installed at the origin of the final circuits to be protected and in AC single-phase circuits not exceeding 230 V. Using an AFDD does not remove the need to apply the other measures in the standard.
The two sections do different jobs, and they are routinely confused. Section 443 decides whether you need protection against transient overvoltages; Section 534 governs the selection and erection of the SPDs themselves. Section 534 was completely revised in 2018, the most significant technical change being the selection requirements for the voltage protection level (Up). Amendment 2:2022 then redrafted Section 443: Regulation 443.4.1 requires protection where the consequence of an overvoltage could cause serious injury or loss of human life, or significant financial or data loss — and for all other cases protection shall be provided unless the owner declares it is not required and accepts the risk. The old risk-assessment method in Regulation 443.5, and Annex A443, were deleted. In practice SPDs are now the default on most new installations.
Section 722 was not new in 2018 — the 18th Edition made significant changes to Regulation 722.411.4.1 on the use of a PME supply, deleting the "reasonably practicable" exception, and revised the requirements for external influences, RCDs, socket-outlets and connectors. Amendment 1:2020 then rewrote the section on the basis of HD 60364-7-722:2018, and Amendment 2:2022 folded that in alongside further changes, including prosumer's installations (722.826.3.201). Section 722 does not apply to wireless (inductive) charging.
Regulation 531.3.3 sets out the RCD types — AC, A, F and B — by how they behave in the presence of DC components and frequencies. Amendment 2:2022 added the sentence that changed specification in practice: RCD Type AC shall only be used to serve fixed equipment where it is known that the load current contains no DC components, with electric heating and simple filament lighting given as examples. Anything with electronics in it — washing machines, dishwashers, EV chargers, LED drivers — needs Type A or better. Most manufacturers now supply Type A as standard for domestic work.
Regulation 521.10.202 replaced 521.11.201 and requires cables to be adequately supported against premature collapse in the event of a fire throughout the installation, not just in escape routes as previously. This is the reason plastic clips alone are no longer acceptable for supporting cables on a ceiling. Amendment 4:2026 added a note explaining the intent of the regulation, and redrafted Regulation 422.2 and 422.2.1 so that 422.2.1 now lists the cables permitted in protected escape routes.
04 · BS 7671 Hub
BS 7671:2018+A2:2022 was issued on 28 March 2022 and could be implemented immediately; BS 7671:2018+A1:2020 remained current until it was withdrawn on 27 September 2022. A2 was a printed reprint of the whole standard — the brown cover — and it is still the version most often quoted second-hand, which is why several A2 changes get misattributed to Amendment 4.
The substantive A2:2022 changes that still matter on site are these. Regulation 411.3.1.2 was redrafted, so main protective bonding applies to extraneous-conductive-parts liable to introduce a dangerous potential difference, with a note clarifying that metallic pipework fed by non-metallic pipes entering the building is not normally an extraneous-conductive-part. Regulation 421.1.7 became a requirement for AFDDs in high rise residential buildings, HMOs, purpose-built student accommodation and care homes. A new Chapter 82 introduced prosumer's low-voltage electrical installations. Regulation 531.3.3 restricted Type AC RCDs to fixed equipment with no DC component in the load current. Appendix 11 (warning and user instruction labels) and a rewritten Appendix 13 on protected escape routes were added.
Regulation group 643.3 was redrafted. Where connected equipment is likely to influence the measurement or be damaged, the Table 64 test is applied before the equipment is connected; then, following connection, a test at 250 V DC is applied between live conductors and the protective conductor, with a minimum acceptable value of 1 MΩ (Regulation 643.3.3).
RCD testing changed at the same time, and Table 3A in Appendix 3 was deleted. Regulation 643.8 now requires the effectiveness of automatic disconnection by RCDs to be verified using test equipment to BS EN 61557-6, and its note says that regardless of RCD type, effectiveness is deemed verified where the RCD disconnects within the stated time on an alternating current test at rated residual operating current (I∆n) — for a general non-delay type, 300 ms maximum. The old half-rated and five-times tests are product-standard tests, not an installation verification requirement in BS 7671.
For the consumer unit itself, A2:2022 is also where Regulation 531.3.2 indent (b) began highlighting the use of RCBOs on individual final circuits in residential premises to minimise unwanted tripping — the practical reason most new consumer units are now fully populated with RCBOs rather than split-load RCDs.
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05 · BS 7671 Hub
BS 7671:2018+A4:2026 was issued on 15 April 2026 and may be implemented immediately. The previous version — BS 7671:2018+A2:2022+Corrigendum (May 2023)+A3:2024 — remains current but is withdrawn on 15 October 2026. Amendment 4 is a substantive amendment: it adds whole chapters and sections, so an older book cannot simply be annotated to match it.
A point of frequent confusion: the electronic amendment issued on 31 July 2024 was Amendment 3 (A3:2024), not Amendment 4. A3 was a very small amendment — two new definitions and one new regulation, 530.3.201, on the use of bidirectional and unidirectional devices.
| Regulation or section | What changed |
|---|---|
| 312.2.1.1 | Now includes a protective neutral bonding (PNB) figure and requirements |
| 421.1.7(a) | Reworded to read "high rise residential buildings" |
| 422.2 and 422.2.1 | Protected escape routes modified; 422.2.1 now lists the cables permitted in a protected escape route, and cables in a fire-resisting enclosure are deemed outside it |
| 434.2.1 and 434.3(a) | "Inherently short-circuit and earth fault proof" introduced for conductor selection and erection |
| Annex B443 | Deleted |
| Table 51 | Revised to identify combined protective and functional earthing conductors, combined protective and functional bonding conductors, and functional bonding conductors |
| Table 52.1 | Now carries the requirements for cables in a wall or partition |
| 537.4.2 | Firefighter's switches now required in locations specified by the fire engineer to support the building's fire strategy; 537.4.2.1 deleted |
| Section 545 (new) | Functional earthing and functional equipotential bonding for ICT equipment and systems |
| 551.7.1 and 551.7.2 | Redrafted for generating sets in parallel — see the panel below |
| Chapter 57 (new) | Stationary secondary batteries; the old Regulation 551.8 requirements moved here |
| 653.1 and 653.2 | Condition reports must take account of the Appendix 6 notes for the person producing the report and include guidance for the recipient |
| Section 716 (new) | Power over Ethernet — distribution of ELV DC power over data cabling |
| Chapter 81 (new) | Energy efficiency, referring to the Building Regulations and BS HD 60364-8-1:2019; Appendix 17 deleted |
| Appendix 4 | Buried cables now have distinct reference methods and current-carrying capacities depending on whether the cable is in direct contact with soil or in a conduit or duct; Tables 4A2, 4D4A, 4E4A, 4H4A and 4J4A revised |
| Appendix 6 | Condition report notes redrafted and items rearranged; code FI no longer needs to be marked as unsatisfactory |
Standard MCBs, RCDs and RCBOs are built to interrupt fault current flowing one way — from the supply, through the device, to the load. Where a battery or PV inverter can export, fault current can flow the other way. Regulation 530.3.201 requires the selection and erection of equipment for protection to take account of the appropriate use of either a unidirectional or a bidirectional protective device; its note points out that product standards require RCCBs, RCBOs, circuit-breakers and AFDDs to be marked to show which they are — "in" and "out", "line" and "load", or arrows. Amendment 4 then redrafted Regulation 551.7.1, which applies where a generating set runs in parallel with another source:
If you install solar PV, battery storage or EV chargers, that combination — 530.3.201, 551.7.1, 551.7.2 and the new Chapter 57 — is the part of Amendment 4 that will change how you specify a job. It affects device selection, where the storage system lands relative to the RCD, and what you record on the certificate.
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Cable sizing, voltage drop, Zs verification, maximum demand, adiabatic equation…
06 · BS 7671 Hub
For a working electrician, BS 7671 is not an abstract academic document — it is the reference you use every day when designing circuits, selecting cables, choosing protective devices, carrying out tests, and completing certificates. Here is how the key parts of the standard map to common on-site activities.
Appendix 4 contains the current-carrying capacity tables for each cable type and reference method, together with the rating factors for grouping, ambient temperature and thermal insulation. Every reference method has its own tabulated capacity — you read the column for the method you are actually using rather than applying a multiplier on top. For voltage drop, Section 525 sets the requirement and Regulation 525.202 points you to Appendix 4, Section 6.4 for the permitted limits. Note that A4:2026 changed the buried-cable methods: direct in soil and in a conduit or duct now have distinct reference methods and distinct capacities.
Part 6 specifies the testing sequence, the tests required, and the acceptance criteria. Every test value you record on an EIC or EICR is compared against the BS 7671 limits. The model forms are in Appendix 6, which since A2:2022 carries separate pages for the schedule of circuit details and the schedule of test results, plus fields for recording SPD and AFDD details.
Chapters 41, 43 and 53 govern how you select protective devices — MCBs, RCDs, RCBOs, fuses — for protection against electric shock, overload and fault current. Regulation 411.3.2.2 sets which final circuits the Table 41.1 maximum disconnection times apply to: circuits rated up to 63 A with one or more socket-outlets, and circuits rated up to 32 A supplying only fixed connected current-using equipment. Tables 41.2 to 41.6 tell you whether the device will disconnect in time at the measured Zs; the adiabatic equation tells you whether the conductor survives the fault for that duration.
When carrying out a periodic inspection you assess the installation against the current edition of BS 7671, recording every departure, defect and deterioration as an observation with a classification code (C1, C2, C3 or FI). A4:2026 touched this directly: Regulation 653.1 requires the Appendix 6 notes for the person producing the report to be taken into account, Regulation 653.2 requires guidance for the recipient to be included, and Appendix 6 now states that code FI no longer needs to be marked as unsatisfactory.
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