Required Tabulated Current Calculator
This tool calculates the required tabulated current-carrying capacity (It) from first principles. It does NOT select a cable for you - after calculating It, you must look up a cable in BS 7671 Appendix 4 withIt ≥ the result, then verify voltage drop and fault protection separately.
Results
Select a cable from BS 7671 Appendix 4 tables withIt greater than or equal to this value.
Voltage-drop check
Worked example
Ib = 32 A, Cg = 0.80, Ca = 1.0, Ci = 1.0.
It = 32 / (0.80 × 1.0 × 1.0) = 40.0 A
Choose a cable whose tabulated current-carrying capacity is at least 40 A, then verify voltage drop separately.
⚠️ Educational design aid. Verify all results against the current BS 7671 edition. Not a compliance tool - does not replace professional engineering judgement or BS 7671 table lookups.
Regulation reference: Per BS 7671 Appendix 4, Section 5.1. The rating factors are defined in BS 7671 Appendix 4, Section 5.2 (grouping), 5.3 (ambient temperature), and 5.4 (thermal insulation).