Bs7671 Cable Sizing ((better)) -

Where ( L ) is the cable length in metres (line + neutral – so for single-phase, use the tabulated mV/A/m directly; for three-phase, note correction).

For any electrical installation operating in the UK, compliance with BS 7671 (IET Wiring Regulations) is not optional—it is a legal benchmark under the Electricity at Work Regulations 1989. At the heart of this compliance lies a process often misunderstood as simple table-lookup: cable sizing . bs7671 cable sizing

[ Z_s = Z_DB + (R_1 + R_2) \times L ]

[ I_z = I_t \times C_a \times C_g \times C_d \times C_i \times C_c ] Where ( L ) is the cable length