United Kingdom · Wiring Regulations examEarthing or bonding?
Earthing connects exposed-conductive-parts to the main earthing terminal to give fault current a path to earth. Protective bonding connects extraneous-conductive-parts to the main earthing terminal so that no dangerous touch voltage can appear between them. Part 2 defines an extraneous-conductive-part as "a conductive part liable to introduce a potential, generally Earth potential".
What do the earth bonding regulations in the 18th Edition ask you to bond?
- A metal water or gas service pipe that is an extraneous-conductive-part. Size the conductor by Regulation 544.1.1 and connect it within 600 mm of the point of entry (Regulation 544.1.2).
- Not a plastic incoming pipe, since plastic can't bring Earth potential in. You still have to check there are no fortuitous connections with Earth.
- Not a metal oil tank itself, though its service pipe may need bonding if it's an extraneous-conductive-part.
- Not metal furniture in a commercial kitchen, which is neither an exposed-conductive-part nor likely to be an extraneous-conductive-part.
Testing and recording bonding
Regulation 643.2.1 requires the continuity of protective bonding conductors to be verified by measuring their resistance; earlier editions only asked for a tick. The IET's typical figures for a 10 mm² conductor run from about 0.01 Ω at 5 m to about 0.09 Ω at 50 m.
To use the armour of an SWA cable as a circuit protective conductor, work out its copper-equivalent size with Table 54.7, using the k values in Table 54.4. Guidance Note 1, Appendix B, has worked examples.
Supplementary bonding and who can do the work
Bathrooms have their own rule for when supplementary bonding can be left out. A gas engineer shouldn't fit protective bonding to gas pipework unless specifically trained and experienced: the Health and Safety at Work etc. Act 1974 and the Electricity at Work Regulations 1989 require anyone doing electrical work to be competent, and Regulation 132.16 requires an assessment of the existing installation first.
Sources: IET and 1 more. Checked October 2026.
Rules and fees can change, so check the official site before your test.
Explore