A common question is how to size a single-core armoured cable buried in the ground to BS 7671. The short answer is that BS 7671 Appendix 4 alone cannot be used, because it does not provide the necessary buried single-core cable data.
BS 7671 permits suitable cables, but Appendix 4 provides 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 not available in BS 7671 Appendix 4.
Agree on the standard for cable sizing with the client, owner, or approving authority, and apply it consistently throughout the design. See the cable sizing standards overview for more context on BS 7671, ERA 69-30 and IEC 60502.