Bs7671 Cable Sizing Link

If voltage drop exceeds the limit, the cable size must be increased – often overriding the thermal sizing for long runs. Even if a cable is correctly sized for load current, it must survive a short circuit fault without insulation damage. BS 7671 provides the adiabatic equation:

[ 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 ] bs7671 cable sizing

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). If voltage drop exceeds the limit, the cable

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 . For any electrical installation operating in the UK,

As the IET itself states: “The tables are a starting point, not the final answer.” Ignoring that principle is the fastest route to a non-compliant – and dangerous – installation. This piece is for educational and reference purposes. Always refer to the latest BS 7671 and consult a qualified electrical engineer for live designs.