Cable: How To Size A

: 3% for power, 5% total including distribution.

$V_d = \frac2 \times L \times I \times (R \cos\phi + X \sin\phi)1000$ (L in meters, Vd in volts) how to size a cable

is given by tables (IEC 60287, NEC Table 310.16). For example: : 3% for power, 5% total including distribution

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. Vd = [2×80×20×(0

$V_d = \frac\sqrt3 \times L \times I \times (R \cos\phi + X \sin\phi)1000$

If calculated Smin > ampacity size, the cable must be upsized for fault survival. For TN systems, a fault between phase and earth must draw enough current to trip the OCPD quickly. The maximum cable length is limited by: