BS 7671 Guide · Section 1

What’s new in Amendment 4

Amendment 4 is now the only current version of the 18th Edition. Here is what changed, what you need to do differently on site, and which parts you can safely leave to the specialists.

Key dates and the transition

The IET and BSI published Amendment 4 on 15 April 2026, and it could be used straight away. There was then a six-month overlap. On 15 October 2026 the previous version, BS 7671:2018+A2:2022+A3:2024, was withdrawn. From that date, new work should be designed to Amendment 4.

There is one exception. If an installation was designed to A2+A3 before the withdrawal date, it can be finished and verified to that version, subject to the contract terms. On long-running projects, check the design date before assuming which version applies.

Amendment 4 does not apply backwards. An installation built to the 16th or 17th Edition is not dangerous just because today’s standard asks for more. When you inspect it, judge it on whether it is safe. Don’t record a departure from the current edition as a defect on its own.

Amendment 3 (2024) has been folded into the main text.

What to cite on certificates

For any work designed on or after 15 October 2026, enter BS 7671:2018+A4:2026 on the EIC, the Minor Works certificate or the EICR. If your forms or software ask for an amendment date, it is 2026. The IET publishes A4 model forms, and scheme providers such as NICEIC and ECA have issued updated certificates and reports. If you are with another scheme, check what it supplies. Switch to A4 forms, and stop using old pads that print the A2 wording.

If a job was designed to A2+A3 and finished after the withdrawal date, cite the version it was designed to and add a short note explaining why. More on the forms in Certificates and EICR codes.

Changes that matter every day

Concealed cables: the new Table 52.1

Regulation 522.6 now comes with a table setting out the options for cables hidden in walls and partitions. It sorts them by two things: whether the wall has metal parts, and whether the cable is less or more than 50 mm below the surface. It gathers the existing rules into one easier view rather than adding new ones.

• Wall with no metal parts, cable under 50 mm deep: either keep the cable in a safe zone and give the circuit 30 mA RCD protection, or use one of the protection methods in Regulation 522.6.204, such as an earthed metal covering or enclosure.
• Wall with no metal parts, cable over 50 mm deep: no extra protection is needed.
• Wall with metal parts (metal stud partitions, for example): depth alone doesn’t get you off. Expect to need 30 mA RCD protection or a 522.6.204 method whatever the depth, and a shallow cable still needs to be in a safe zone unless it has 522.6.204 protection. Check Table 52.1 for the exact combinations.

The safe zones are the same as before. They run within 150 mm of the top of the wall and within 150 mm of a corner, and straight out horizontally or vertically from an accessory or switchgear.

RCD types in series

Regulation 531.3.3, together with new Figure A53.2, deals with “blinding”. This is where DC fault current saturates a less capable upstream RCD so it can’t trip. The rule is that every RCD in the chain must suit the residual currents it might see. In practice:

• No Type AC upstream of Type A, F or B.
• No Type A upstream of Type F or B.
• No Type F upstream of Type B.

The one exception: a Type AC, A or F RCD may sit upstream of a Type B where the RCD manufacturer specifically declares the arrangement suitable. This comes from an informative note to Regulation 531.3.3, so check it and Figure A53.2 in your copy.

This matters most when you add an EV charger, heat pump or battery inverter to an existing board protected by a Type AC or Type A main switch RCD.

AFDDs and the 18 m threshold

Regulation 421.1.7 previously required AFDDs in “higher risk” residential buildings. That term was easily confused with the definition in the Building Safety Act, so it now reads “high-rise residential buildings”. This means domestic buildings with a storey more than 18 m above ground level. The requirements for HMOs, purpose-built student accommodation and care homes have not changed. In other premises, AFDDs are still recommended for single-phase final circuits supplying socket-outlets rated up to 32 A.

There is one useful clarification. Under Regulation 722.421.1.7.201, a circuit supplying EV charging equipment made to BS EN 61851, using sockets or connectors to BS EN IEC 62196-2, doesn’t need an AFDD. For more on fire protection, see Fire, arc fault and surge.

Terminating fine-stranded conductors

Regulation 526.2 now says the connection method must suit the conductor class. Regulation 526.9.1 adds that the ends of stranded and fine-wire conductors must not be able to splay out. Table 52.4 sets out the classes: Class 1 is solid, Class 2 is stranded, Class 5 is flexible and Class 6 is very flexible.

Fine strands crushed under a screw can loosen, heat up and arc. Either use a terminal rated for that conductor class or treat the end, normally with a correctly crimped bootlace ferrule.

Protective neutral bonding (PNB)

Regulation 312.2.1.1 now recognises PNB as a form of TN-C-S, with its own new figure. PNB is used where there is a single source, typically a private or dedicated transformer, and where PME is not allowed or not recommended under the ESQCR and ENA guidance. The PEN conductor is connected to earth as close as practical to the consumer’s supply terminals. This limits the voltage rise if the PEN breaks. If a supply is described as PNB, record it correctly on the certificate. Don’t assume it is ordinary PME. For more, see Earthing and bonding.

Two-way power: generators and batteries

More homes now have solar, batteries and vehicle-to-home charging. This means current can flow in either direction through a board. Regulation 530.3.201 requires you to choose unidirectional or bidirectional protective devices to suit. A device marked for one direction (with “line/load” terminals or an arrow) must not be fed backwards.

Regulation 551.7 has also been tightened:

• A bidirectional device is needed wherever energy can flow both ways.
• There are limits on connecting a source to the load side of an RCD.
• A generating set must connect on the supply side of all the protective devices for the final circuits. A stationary battery counts as a generating set, not as a load.
• Where a generator runs in parallel with the supply, the rating of the board has to allow for both sources. You can’t rely on diversity to make it fit.

For battery and inverter installs in detail, see EV, solar, batteries and heat pumps.

EICR changes

Regulation 653.1 now requires the EICR to follow the model form in Appendix 6. Regulation 653.2 requires the report to include guidance for the person receiving it, and that guidance has been rewritten. You can now attach photographs and thermal images to support what you found, which is useful when you’ve given a code that a landlord may dispute. The EIC and Minor Works forms have only minor changes, but the EICR has changed substantially. The biggest practical change: a C3 or FI on its own no longer makes a report unsatisfactory, and FI now reads as investigation “advised”. For coding, see Certificates and EICR codes.

Regulation references: 312.2.1.1, 421.1.7, 522.6, 526.2, 526.9.1, 530.3.201, 531.3.3, 551.7.1, 551.7.2.1, 653.1, 653.2, 722.421.1.7.201

Specialist changes in brief

Most domestic jobs won’t touch these, but know they exist so you can spot when a job goes beyond your usual scope.

Also new: Section 545 on functional earthing for ICT equipment, and reference method D2 in Appendix 4 for buried cables.

Regulation references: Chapter 57, Section 545, 702.55.5, Section 710, 714.411.3.4, Section 716, 422.2.201, 422.2.202, Table 51, Chapter 81

What to do now

1. Make sure you have the Amendment 4 book, or access to it.
2. Update your certification software and throw out old paper forms.
3. Check the RCD types on any board before adding EV, heat pump or battery circuits.
4. Carry ferrules and a crimper as standard kit.
5. Book an update course if you haven’t had formal training on the changes.