BS 7671 wiring regulations
The green-and-yellow colour combination in a fixed installation is reserved exclusively for which type of conductor?
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What is BS 7671?
BS 7671, Requirements for Electrical Installations, is the British Standard for electrical installation work in the UK, published jointly by the IET and BSI as the IET Wiring Regulations. It is in its 18th Edition, and the current version is BS 7671:2018+A4:2026. It is not law in itself, but it is the benchmark that inspections, competent-person schemes and landlords’ electrical checks are measured against. The questions above test the parts people are most often asked about.
BS 7671 at a glance
- Full title
- Requirements for Electrical Installations. IET Wiring Regulations
- Current version
- BS 7671:2018+A4:2026
- Amendment 4 published
- 15 April 2026
- Previous edition
- With A2 and A3: withdrawn 15 October 2026
- Structure
- Eight parts, then the appendices
- Legal status
- Non-statutory, but named in law for rented homes
Dates and structure as published by the IET and BSI, checked 23 September 2026. Until 15 October 2026 installers may work to either edition; from that date Amendment 4 must be used.
How BS 7671 is organised
A regulation’s number tells you where it lives: the first digit is its part, the next its chapter. Part 2 matters more than it looks, because many disagreements turn out to be about a defined term. The appendices carry most of the numbers, including the cable current-carrying capacity and voltage drop tables in Appendix 4 and the device characteristics in Appendix 3, so knowing which appendix holds what is the most useful navigation skill in an open-book assessment.
| Part | Title | What you find there |
|---|---|---|
| 1 | Scope, object and fundamental principles | What the standard covers, and the principles every installation must meet |
| 2 | Terms and definitions | The defined terms the rest of the standard relies on |
| 3 | Assessment of general characteristics | The supply, the earthing arrangement (TN-S, TN-C-S, TT or IT) and what the installation is for |
| 4 | Protection for safety | Protection against electric shock, thermal effects, overcurrent and voltage disturbances |
| 5 | Selection and erection of equipment | Cables and wiring systems, protective devices, earthing and bonding, and batteries |
| 6 | Inspection and testing | Initial verification, periodic inspection, and the certificates and reports |
| 7 | Special installations or locations | Bathrooms, swimming pools, construction sites, EV charging, solar PV, medical locations and more |
| 8 | Functional requirements | Energy efficiency, and installations that generate or store their own energy |
What Amendment 4 changed
Amendment 4 was published on 15 April 2026. It gathers every earlier amendment, including Amendment 3, into one volume and adds and rewrites material:
- Chapter 57, a new chapter on stationary secondary batteries.
- Section 716, a new section on Power over Ethernet, the DC power carried on data cabling.
- New requirements for functional earthing and bonding of information and communication technology equipment.
- A major revision of Section 710, medical locations.
- Energy efficiency moved out of Appendix 17 and into Part 8 as Chapter 81.
- On a condition report, FI now means further investigation is advised, and a C3 or FI on its own no longer makes the report unsatisfactory.
| Version | Issued | What it did |
|---|---|---|
| BS 7671:2018 | 1 July 2018 | The 18th Edition, in force from 1 January 2019 |
| A1:2020 | 1 February 2020 | Revised Section 722, electric vehicle charging |
| A2:2022 | 28 March 2022 | A major amendment that added Part 8, for prosumer installations |
| A3:2024 | 31 July 2024 | Bidirectional and unidirectional protective devices; used alongside the A2 book |
| A4:2026 | 15 April 2026 | Every amendment in one volume, plus the changes above |
Is BS 7671 the law?
Not in itself. HSE describes the Wiring Regulations as non-statutory, and the Electricity at Work Regulations 1989 never name them; following BS 7671 is, in HSE’s words, likely to achieve compliance with the relevant parts of those regulations.
Other law points at it directly. In England, the electrical safety regulations for rented homes define the standard an installation must meet as the 18th Edition, BS 7671:2018, and require an inspection at least every five years; they now cover social housing as well as private lets. Wales names BS 7671:2018+A2:2022 in its equivalent rules.
Part P of the Building Regulations requires reasonable provision for electrical safety in dwellings. BS 7671 is how that is met in practice, although Approved Document P still cites the 2008 edition.
What BS 7671 requires that people get wrong
Earthing and bonding arrangements follow from the supply type, not from habit. A PME supply needs main bonding sized against the supply neutral conductor; a TT installation depends on its own electrode and an RCD for fault protection.
Cable selection is a coordination chain: design current, then device rating, then cable capacity after grouping, ambient temperature and thermal insulation have reduced it. Skipping a step in that chain is the classic error.
RCD type is matched to the residual current the device must detect, not to the name of the circuit. Loads with electronic components can produce residual currents a Type AC device will not see.
Certificates and reports
Appendix 6 holds the model forms. An Electrical Installation Certificate covers new installations and work that adds a circuit; a Minor Electrical Installation Works Certificate covers smaller additions and alterations that do not; an Electrical Installation Condition Report records the condition of an existing installation.
A condition report codes each observation: C1, danger present; C2, potentially dangerous; C3, improvement recommended; FI, further investigation. Under Amendment 4 the report is unsatisfactory when any C1 or C2 is recorded; C3 and FI are recommendations.
The standard is copyright of the IET and BSI, so this page explains its structure and principles without reproducing regulation text. Buy the current edition from the IET or BSI for the authoritative wording.
BS 7671, the On-Site Guide or Guidance Note 3?
BS 7671 contains the installation requirements. The On-Site Guide helps with common arrangements within its scope, and Guidance Note 3 develops inspection and testing. Match the book to the task and check its edition before using it.
Common questions
Is BS 7671 a legal requirement?
Not in itself: it is a British Standard, and HSE calls it non-statutory. But the rules for rented homes in England and Wales name it, Part P work is judged against it, and following it is the usual way to show compliance with the Electricity at Work Regulations.
What is the current version of BS 7671?
BS 7671:2018+A4:2026, published on 15 April 2026. The previous edition, with Amendments 2 and 3, stays valid until 15 October 2026; from that date Amendment 4 must be used.
What is the difference between BS 7671 and the 18th Edition?
They are the same document. BS 7671 is the standard’s number, and the 18th Edition is the edition first issued in 2018, since amended four times. "18th Edition" is also the common name for the qualification assessed against it.
How many parts does BS 7671 have?
Eight. Part 8, Functional requirements, arrived with Amendment 2 in 2022 for installations that generate or store energy, and Amendment 4 added energy efficiency to it as Chapter 81. The appendices follow the parts and hold the tables.
Is there a 19th Edition of the Wiring Regulations?
Not yet. The IET has not announced one, and Amendment 4 is the current version of the 18th Edition. The IET says a new revision of BS 7671 is usually published every four years.
Do I need to own a copy of BS 7671?
For a City & Guilds 2382 assessment, you need access to the permitted edition of BS 7671. Check whether your centre supplies the examination copy before buying one, and confirm the edition and permitted markings. For installation work, use the current standard.
What is the IET On-Site Guide?
A practical companion to BS 7671 for competent installers working within its scope, up to 100 A three-phase. It supports the full standard and does not replace it. For the City & Guilds 2382-26 exam, the permitted reference book is BS 7671 itself; the On-Site Guide is not permitted.
Revision to support these questions
Keep going
Knowing where a requirement lives in BS 7671 is worth more in an open-book assessment than remembering the number. PlumbRevise covers the standard part by part, with the 2391 inspection and testing bank alongside it.