BS 7671 cable selection standards
UK electrical regulations require conductors to meet current-carrying capacities in Appendix 4 (Table 4D5 for flat twin & earth, Table 4D4 for SWA).
Voltage drop must not exceed 3% (6.9V on 230V) for lighting circuits or 5% (11.5V on 230V) for general power circuits from the supply origin.
Worked example: UK 32A ring final circuit
A standard UK 32A socket ring circuit uses 2.5 mm² twin & earth with 1.5 mm² CPC, protected by a 32A Type B MCB.
For a 32A radial circuit or high-power cookers, 4.0 mm² or 6.0 mm² cable is typically required.
UK cable sizing inputs
Installation Method
Select Method C (clipped direct), Method B (in conduit), or Method 100 (in thermal insulation).
CALCULATOR QUESTIONS
UK BS 7671 cable sizing calculator questions
What cable size is needed for an EV charger in the UK?
A typical 7.4 kW domestic EV charger draws 32A at 230V and generally requires a minimum of 6 mm² twin & earth or 3-core SWA cable.
What is the voltage drop limit under BS 7671?
BS 7671 recommends a maximum 3% drop for lighting (6.9V) and 5% drop for power loads (11.5V) on a 230V single-phase supply.