18th Edition On-Site Guide

The 18th edition on-site guide is an accompanying piece of documentation that complements the full 18th edition bs7671 wiring regulations guide. Its release date was aligned to the launch of the main book, and entered the industry officially in the same month (January 2019).

As the title suggests, the book is used as an on-site consultation aid. In a nutshell, the guide facilitates a more practical application of the regulations cited in the bs7671 guide. This is not to say the latter does not offer a similar advantage, the main book is also designed with real-world uses in mind. However, if the 18th edition wiring regulations guide is the classroom-based literature, then the on-site guide is the live, on-the-job working document.

A leaner, sharper version

Given that its main use is to provide on-task support, the on-site guide is more concise, shorter in length, and more user-friendly than the full bs7671 text. Furthermore, its increased use of supplementary tables, graphs, and diagrams often helps the reader to acquire information more readily. The book is just under half the size of its fuller cousin (224 pages vs. 560 pages).

However, in no way should this article be used as a replacement to the larger format guide. This is particularly true if you’re a student of the industry, a relative novice, or revising for a full or update course examination. Understand the different functions of the books, and apply them to the right context.

The on-site guide also encourages the reader to consult the bs7671 in cases where regulatory compliance is unclear. The full, unabridged regulations will always be present in the main guides, regardless of the edition number.

‘Real-world’ application

The layout and structure of the guide is extremely similar to the full version. A numbering system is in-play, and, although the level of detail is reduced, users can still find the location of information in the same way. It’s also important to note that some information included is not referenced in the main 18th edition bs7671. It is therefore advisable that both documents are read thoroughly, and notes are made of key differences.

As alluded to, the guide is designed to help installations for electricians and trade professionals. In its own words, this relates to:

  • Domestic and similar installations, including off-peak supplies, supplies to associated garages, outbuildings and the like; and
  • Small industrial and commercial single- and three-phase installations.

Information on Special Installations & Locations (Part 7 in the 18th edition bs7671) is only mentioned sparingly in this guide. However, some notes are included on the specific sections relating to Bathroom & Shower fittings, as well as advice on underfloor heating installations.

The on-site guide accommodates relevant information on installations that:

  • Supply frequency’s up to 50Hz
  • Have a nominal voltage of 230V AC single-phase or 400/230V AC three-phrase
  • Supply through a distributors cut-out having fuse(s) rated at 100A or less to one of either BS 88-2, BS 88-3, BS 88-6 or BS 1361 Type II standards

Useful, additional notes

The book also includes information on elements that may need to be considered during general installations. This includes, but is not limited to, content on conduit and trunking capacities, bending of radii cables and

Content on standard circuits usage, which is not referenced in the main book, is included in Section 7. It should be noted that as the table in this section only offers overview guidance, the numbers used may not provide optimum economical options.

In the spirit of consistency, the definitions and terminology used in Part II of the main guide are deployed in the on-site version. This should allow candidates to find corresponding detail quickly.

If further guidance is required on elements published in either the on-site or 18th edition bs7671 books, then candidates may want to explore a collection of handy guidance notes published by the IET (Institute of Engineering and Technology). Although these do not examine all content covered, eight key parts & sections are re-reviewed.

Sections and Appendices – An Overview

It would be impossible to cover all of the detail pertained in the book within a summary article. However, please see below a list of key sections and Appendices sub-headings, which should help you to understand what items are broadly available.


  1. Introduction
  2. Electrical Supply
  3. Protection
  4. Earthing & Bonding
  5. Isolation & Switching
  6. Labelling
  7. Final Circuits
  8. Locations containing a bath or shower
  9. Inspection & Testing
  10. Guidance on Initial Testing of Installations
  11. Operations of RCDs (residual current device)


A. Maximum demand and diversity

B. Maximum permissible measured earth fault loop impedance

C. Selection of types of cable for particular uses and external influences

D. Methods of support for cables, conductors and wiring systems

E. Cable capacities of conduit and trunking

F. Current-carrying capacities and voltage drop for copper conductors

G. Certification and reporting

H. Standard circuit arrangements for household and similar installations

I. Resistance of copper and aluminium conductors

J. Selection of devices for isolation and switching

K. Identification of conductors

L. Degrees of protection provided by enclosures (IP code)

N.B. It’s worth noting that in Appendix G, the guide provides useful mock certification. This allows candidates to observe an array of realistically completed documentation. The examples of Minor Electrical Installation Works and Electrical Installation Condition Reports (EICRs) certificates are particularly helpful.

In Summary

So, there you have it, a full overview of the 18th edition on-site guide. In approaching this key text, our top tips would be:

  • Acquire a strong grasp of which book is more relevant in any given moment or works. Is it the full 18th edition bs7671 guide or the condensed on-site version? With reference to the former, candidates should deploy the full version if they need regulation detail, or require additional information around a chosen topic. For the latter, this may include consulting the documentation just prior to commencing practical works, on-site, with piers and supervisors.
  • Never use the on-site guide as a direct substitute to the full book!
  • Read, digest and understand the additional content offered.
  • Familiarise yourself with the structure, format and general tone of the guide.
  • Always look to cross-reference information provided with the 18th edition full guide when necessary.

In essence, the on-site guide is the perfect accompanying tool to the full 18th edition bs7671 book. Ensure you treat it as such, and exploit opportunities for its use.