BS 7671 Reference Methods

Reference Methods are codes used to describe the various installation methods for the installation of electrical wiring and cables as set out in BS 7671 Appendix 4, Section 7. Methods of Installation, and are used to determine the current carrying capacity of a cable depending on the reference method employed for each cable type which is required for accurate cable sizing.

This explanation will guide you though the all the installation reference methods, codes and their applications, uses and descriptions.

Reference Method Codes

BS 7671 electrical reference method wiring codes include installation reference methods A, B, C, D, E, F, G, 100, 101, 102 and 103.

Methods 100, 101, 102 and 103 refer only to flat twin and earth cables installed in thermal insulation.

See BS 7671 Table 4A2 – Schedule of installation methods of cables of BS 7671 for determining the current-carrying capacity of cables.

Reference Methods

The main reference methods and descriptions are,

Reference Method A = Enclosed in conduit in a thermally insulated wall.
Reference Method A = Multi-core cable direct in a thermally insulated wall.
Reference Method B = Enclosed in conduit or trunking on a wall.
Reference Method C = Clipped Direct.
Reference Method C = On unperforated tray, (with item 2 of table 4C1).
Reference Method D = Buried directly in the ground or within a duct in the ground.
Reference Method E = Single-core on perforated cable tray or ladder rack.
Reference Method F = Multi-core cables on perforated cable tray or ladder rack.
Reference Method G = Bare or non-sheathed cables on insulators.

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BS7671 table 4A2 details the specific applications of the reference methods as various installation methods may be covered by the same reference method code.

It is important to note that not all cable types are suitable for every type of Reference Method, for example, it is not permitted to install flat twin and earth cables directly in the ground (Reference Method D).

Twin and Earth Reference Methods

The following reference methods are only applicable to flat twin & earth cables in thermal insulation.

Reference Method 100 = Above a plasterboard ceiling covered by thermal insulation NOT exceeding 100mm.
Reference Method 101 = Above a plasterboard ceiling covered by thermal insulation EXCEEDING 100mm.
Reference Method 102 = In a stud wall with thermal insulation with the cable TOUCHING the inner wall surface.
Reference Method 103 = In a stud wall with thermal insulation with the cable NOT TOUCHING the inner wall surface.

Reference methods 100, 101, 102 and 103 do not apply to any other cable type other than flat twin & earth cables, see tables 4A2 and 4D5 of BS 7671.

For a full and exact description of all the different electrical installation reference methods listed in BS 7671, see Appendix 4, section 7 (page 430) onwards.

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