Reference Methods are codes used to describe the various installation methods for the installation of electrical wiring and they can be found in Appendix 4, 7. Methods of Installation, which are used to determine the current carrying capacity of a cable depending on the reference method employed.
BS 7671 reference method wiring codes include reference methods A, B, C, D, E, F, G, 100, 101, 102 and 103.
Methods 100, 101, 102 and 103 refer to twin and earth cables installed in thermal insulation.
See, Table 4A2 – Schedule of installation methods of cables (including Reference Methods) for determining current-carrying capacity, (page 433).
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.
Note: Table 4A2 details 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 Reference Method, i.e. It is not permitted to install flat twin and earth cables directly in the ground.
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 table 4A2 (page 437) of BS 7671 and table 4D5.
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) and onwards.
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