Bs7671 Cable Sizing [best] Jun 2026

For a circuit protected by a 32A MCB, if ( C_a = 0.87 ) and ( C_g = 0.8 ), then ( I_t ) must be at least ( 32 / (0.87 \times 0.8) = 46A ) from the table – a much larger cable than intuition suggests.

BS 7671:2018+A2:2022 Requirements for Electrical Installations provides the governing standards for this process in the United Kingdom. This paper delineates the specific steps and formulas required to achieve compliance. bs7671 cable sizing

The general equation is: $$I_t \geq \fracI_nC_a \times C_g \times C_i \times C_f$$ For a circuit protected by a 32A MCB, if ( C_a = 0

32A MCB (Type B).

For a final circuit: