The most reliable formula for cable sizing (especially for longer runs) uses voltage drop as the limiting factor. For a single-phase AC or DC circuit:
For a three-phase circuit:
[ A = \frac2 \times \rho \times I \times LV_d ] how to calculate cable size in sq mm formula
[ A = \frac\sqrt3 \times \rho \times I \times LV_d ] The most reliable formula for cable sizing (especially