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.
Table 4D2A, Method C – 6mm² Cu (47A) is insufficient; 10mm² Cu (64A) works. bs7671 cable sizing
10mm² twin and earth PVC copper.
[ I_z = I_t \times C_a \times C_g \times C_d \times C_i \times C_c ] For a circuit protected by a 32A MCB, if ( C_a = 0
The 18th Edition Amendment 2 also clarified requirements for (soil thermal resistivity default 2.5 K·m/W) and thermally insulated walls . bs7671 cable sizing
BS7671 provides several tables and charts to help with cable sizing, including: