Know the numbering of BS7671

A previous post in this series talked in detail about the structure of BS7671 Wiring Regulations. Now we take a look at how the Parts and Sections are numbered.

One of the secrets of success with the 18th Edition is to be able to find your way around the Regs book. This is made much easier by understanding the numbering system. With understanding you can quickly locate the relevant regulations both to assist you in your work as an electrician and beforehand when aiming to pass City & Guilds 2382 exam.


The numbering of the 18th Edition Wiring Regulations follows the pattern of the technical intent of Standards developed at the European CENELEC level (which is not affected by Brexit). The system is based on the harmonisation documents HD60364 series of standards.

Or, in language the rest of us understand, the numbering system has designed to be consistent, easy to follow and easy to update.

For the old timers amongst us who wired our first socket under the 16th Edition Regulations, the most obvious change came when the 17th Edition Wiring Regulations dropped the dashes and since then the Regs use a point/dot numbering system, based on the IEC numbering system.

So, what does this show?

It shows Regulation 524.1 which is ‘The cross-sectional area of each conductor in a circuit shall be not less than the values given in Table 52.3, except as provided for extra-low voltage lighting installations according to Regulation 715.524.201.’

The Regulation is located in Section 524 – Cross-sectional areas of conductors

Section 524 is located in Chapter 52 – Selection and Erection of Wiring Systems

Chapter 52 is located in Part 5 – Selection and Erection of Wiring Equipment

Easy! All the BS7671 Wiring Regulations are numbered in this way.

But, because we are British and are working with a European institution (Cenelec), we of course wanted something a little bit special for ourselves.

From Amendment 3 regulations which are numbered .200 to .299 are applicable to Britain alone. This is a change from 1st and 2nd Amendments of BS7671 where UK only regulations were numbered .100 to .199. Going forward all .100 regulations will be changed to .200 regulations when that regulation requires a substantial rewrite.

In the example above, you can see reference to Regulation 715.524.201 ‘The minimum cross-sectional area of the extra-low voltage conductors……..’. That the Regulation number is 524.201 shows that it is a regulation for the UK only and has been substantially rewritten (and in this example: 15 is the Section, which is in Chapter 1 of Part 7).

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