How To: Size A Cable

Example : 230 V single-phase, L=80 m, I=20 A, cosφ=0.85, 4 mm² Cu (R=4.6 Ω/km, X=0.09). Vd = [2×80×20×(0.0046×0.85 + 0.00009×0.526)] / 1000 = 12.8 V → 5.6% > 3%. Fail. Increase to 6 mm². During a short circuit, heat is generated faster than it can dissipate (adiabatic process). The cable must survive until protection clears the fault.

| Copper, XLPE, 90°C, 30°C ambient, free air | 1.5 mm² → 24 A | 2.5 mm² → 32 A | 4 mm² → 42 A | | Aluminum, PVC, 70°C, buried | 16 mm² → 70 A | etc. | how to size a cable

is given by tables (IEC 60287, NEC Table 310.16). For example: Example : 230 V single-phase, L=80 m, I=20 A, cosφ=0