Introduction

Industry practitioners have six months of grace period (which ends on 15^th October 2026), where work can be conducted to either BS 7671 18^th Edition Amendment 2 and 3 together OR to BS 7671 18^th Edition Amendment 4.

On 16^th October 2026, only BS 7671 18^th Edition Amendment 4 will be deemed as the current standard.

Therefore, the clock is ticking on industry practitioners to demonstrate their competence.

This article will cover a selection of top ten changes to the standard.

The cover

As BS7671:2018+A2(2022) had a BROWN coloured cover, the expectation was that Amendment 4 would revert back to RED.

After deliberation in the committee it was seen to be more prudent to reserve the RED cover for new editions of the standard as opposed it being used for amendments to existing editions.

As such, the decision was made to select a colour which harps back to a bygone age. ORANGE was last used in 1976 with the final variant of the Fourteenth Edition. So it is nice to see a revival of the bright orange or pumpkin coloured cover.

Part 2 – Definitions

Part 3 – TN-C-S PNB Earthing Systems

Unlike other earthing systems (with the exception of specialist IT earthing systems), PNB systems are not earthed at the source end. Instead due to the rural nature of such supplies, the source earth is generally located within 40m of the consumers installation (according to G12/4 engineering recommendations produced by the Energy Networks Association (ENA)), where an earth rod is driven into the general mass of Earth.

The earth is derived from the neutral block where it connects to both a main earthing terminal to facilitate connection of the main earthing conductor for the consumers installation and the earth rod.

Figure 3.9B – TN-C-S PNB Earthing System, BS7671:2018+A4(2026)

So, if the responsibility for such an arrangement remains the responsibility of the distributor why is it important for electrical contractors to know?

The main reasons are firstly to understand the maximum external earth loop impedance value to ensure that the consumers installation remains compliant as regards choice of protective device and levels of fault current to ensure quick disconnection of circuits in the event of a fault.

Secondly, earthing system information impacts the design in relation to the presence of the Protective-Earth Neutral (PEN) conductor. With such (TN-C-S) systems larger levels of fault current exist in the in the neutral conductor under fault conditions. These need to be considered in order to not exceed the touch current limits of the installation which would pose a serious shock risk to users of the installation. Suitable protection for the system is then achieved by BS 7671 requiring larger cross-sectional area for equipotential bonding conductors when dealing with TN-C-S earthing systems than with other earthing systems such as TT or TN-S.

The benefit for the electrical contractor is that due to extremely low risk of loss of PEN (or the neutral-earth link) in TN-C-S PNB systems due to this direct connection between the main earthing conductor and the source earth, some DNOs permit the equipotential bonding requirements associated with a TN-S system instead. Thus leading to a reduced cross sectional area of the equipotential bonding conductors and reduced copper usage, together with a faster simpler installation and lower material and labour costs overall.

However, it is imperative for electrical contractors to double check the DNO requirements responsible for maintaining the network in the area of work, as some distributors may still require PME conditions to be satisfied.

Part 4 – 422 & Appendix 13

A protected escape route is defined as “A fire sterile, usually unpainted or carpeted – grey concrete part of the building where escape routes are maintained for people to reach places of ultimate safety.”

Appendix 13 supports the regulations with Section 422 and provides general information on escape routes, information on the types of cables to be used and the final section tackles the topics of fire sealing and building penetrations.

Part 5 – 531.3.3 A53.2

As a reminder, there are four main types of RCDs recognised by BS 7671, each with its own set of characteristics and symbol.

1. Type AC which provides protection against residual sinusoidal alternating currents, whether suddenly applied or slowly rising.
2. Type A which provides all the protection of a Type AC device AND residual pulsating direct currents and residual pulsating direct currents superimposed on a smooth direct current of up to 6 mA.
3. Type F which provides all the protection of a Type A device AND for residual pulsating direct currents superimposed on a smooth direct current up to 10 mA.
4. Type B which provides all the protection of a Type F device AND residual pulsating direct currents superimposed on a smooth direct current typically up to 60 mA or more.

Figure A53.2 is a new figure added in Amd4 of BS 7671, which if considered, would ensure that upstream devices are protected against the effects of “blinding” in the presence of DC leakage or fault current.

Figure A53.2 Consideration of RCD types in series

Covering the figure (from left to right) we have:

1. A Type A device has a Type AC devices connected downstream. (The type A is more capable than the AC – so this is fine).
2. Two type A devices in series, but the most upstream one is a Selective or time-delayed type – ensuring it will not trip faster than the general type A which is downstream of it.
3. Either one Type B or One Type F – the crux here is that the point of connection is upstream of the time-delayed Type A (as indicated by the point of connection being the larger black circle in Figure A53.2) and thus coordination remains.

This can occur as through robust product development and testing, the manufacturer would be fully aware of the physical limitations of their device by analysing items such as the materials used within the RCD core, the internal arrangement of components and the various set points within software.

The intimate knowledge of their product allows that deeper understanding of the pinch points and where RCD devices in series are at risk of DC blinding. Which, from a contractor’s perspective provides the assurance to follow the manufacturer’s instructions.

The Tesla Training Team have produced other guidance on the topics of the different types of RCDs and the effects of DC blinding, which are well worth a read too.

Type AC RCDs and the effects of DC leakage current – Tesla Technical Training LTD

Part 5 – Section 545

Datacentres are likely to be the next major global growth area as such BS7671 (influenced by work happening at international level) has brought this section into the standard with Amendment 4 to the 18^th edition.

It is important to understand that functional bonding is used for any reasons other than safety. Some specific items of equipment need functional bonding to prevent loss of data transmission or for noise reduction due to electromagnetic interference or capability (EMI/EMC).

Part 5 – 551.7.1

1. protection against thermal effects in accordance with Chapter 42 and protection against overcurrent in accordance with Chapter 43 shall remain effective in all situations;
2. where an RCD is providing additional protection in accordance with Regulation 415.1 for a circuit connecting the generator set to the installation, the RCD shall disconnect all live conductors, including the neutral conductor;
3. protective devices shall be selected in accordance with Regulation 530.3.201 (for bidirectional capability);
4. except where the RCD disconnects all live conductors, including the neutral conductor, a source of supply shall not be connected to the load side of any RCD providing additional protection in accordance with Regulation 415.1 that is shared with other circuits.

Part 5 – Chapter 57

Another resource which may be of interest is PAS 63100:2024. A PAS or Publicly available specifications are codes of practice for specific areas of interest that are commissioned by third party organisations. The BSI typically helps to facilitate PAS production and once completed, PAS documents become freely available resources for any interested stakeholders.

In this case, PAS 63100 was sponsored by the Department of Energy Security and Net Zero and covers the topic of Electrical installations – Protection against fire of battery energy storage systems for use in dwellings – Specification.

https://www.bsigroup.com/siteassets/pdf/en/insights-and-media/insights/brochures/pas-63100-2024.pdf

Part 7 – Section 716

Application such as, smart security systems, CCTV, wireless access points, VoIP phones, and the whole push of Internet of Things –controls for lighting, HVAC, access control, environmental sensors, public signage as common-place use cases.

BS 7671 permits the use of ethernet cable to DC power of up to 750 mA over an ethernet cable.

There are different categories of ethernet cables, each with properties including the speed of data transmission and bandwidth including;

1. Cat5 – 100 Mbps – bandwidth 100 MHz
2. Cat6 – 10 Gbps – bandwidth 250 MHz
3. Cat7 – 10 Gbps – bandwidth 600 MHz
4. Cat8 – 25-40 Gbps – bandwidth 2000 MHz

Therefore it is nice to see PoE and Section 716 in BS7671.

Part 8 – Chapter 81

1. Approved Document L, Conservation of fuel and power, Volume 1: Dwellings – England, and Approved Document L, Conservation of fuel and power, Volume 1: Dwellings – Wales.
2. Approved Document L, Conservation of fuel and power, Volume 2: Buildings other than dwellings – England, and Approved Document L, Conservation of fuel and power, Volume 2: Buildings other than dwellings – Wales.
3. Scottish Government Building Standards Division Domestic Technical Handbook.
4. Scottish Government Building Standards Division Non-domestic Technical Handbook.
5. Technical Booklet F1 for dwellings – Northern Ireland.
6. Technical Booklet F2 for buildings other than dwellings – Northern Ireland.

However, as this Harmonised Document provides additional requirements, measures and recommendations for the design, erection, operation, and verification of all types of low voltage electrical installation including local production and storage of energy for optimizing the overall efficient use of electricity. Designers may therefore find it helpful to supplement the advice given in Chapter 81 with additional information as outlined in BS HD 60364-8-1.

Conclusion

A deeper dive into the changes is required to answer questions such as;

• Have the model forms changed and if yes, how?
• Which new protective device has been included for EV charging equipment?
• How have the requirements for medical locations and other special locations changed?
• What’s the new installation reference method?
• Are BS 88 series fuses still a thing?
• What does it mean by presumption of conformity in relation to product standards?
• What is the rating of a BS 1363 socket outlet?

Complete the training now (by visiting the link above) in readiness to prove competence at your next annual Competent Person Scheme (CPS) audit OR simply to understand the changes and, more importantly, how they impact you and your business.

C&G Exam

The remote option is fully organized by City and Guilds invigilators who, once booked through our website, will be in touch to confirm a convenient date and time for your exam.

Please note, the examination consists of 60 questions and covers the entire book (not just the changes with Amendment 4). The duration is 2 hours, and you must achieve 36 correct answers out of 60 ( or 60%) to pass the assessment.

BS 7671:2018+A4 (2026) Requirements for Electrical Installations, IET Wiring Regulations – 18th Edition Incorporating Amendment 4 – Updates Course | Tesla Technical Training Ltd