A common question is how to size an armoured single-core cable buried in the ground to BS 7671. The short answer is that this is not possible using BS 7671 Appendix 4 alone, because the necessary buried single-core cable data is not provided there.
BS 7671 permits the use of suitable cables, but Appendix 4 contains buried-cable current rating data for multicore cables rather than single-core armoured cables. A practical alternative is to use another recognised sizing standard that includes the required installation methods and rating data.
Using ERA 69-30 as an alternative
ERA 69-30 includes installation methods and sizing data for buried single-core cables. It is therefore a suitable reference when the design requires buried single-core cable sizing data that is not available from BS 7671 Appendix 4.
The standard selected for cable sizing should be agreed with the client, owner or approving authority and applied consistently throughout the design. See the cable sizing standards overview for more context on BS 7671, ERA 69-30 and IEC 60502.
Video example
The original article included the following video example showing the approach.