How - To Size A Cable

Example : 2.5 mm² PVC copper (30 A tabulated), ambient 45°C (k₁=0.79), 4 circuits (k₂=0.65) → effective = 30×0.79×0.65 = 15.4 A. For a 16 A load, this cable fails. Increase to 4 mm². Voltage drop reduces torque in motors, causes flicker in lights, and wastes energy.

is given by tables (IEC 60287, NEC Table 310.16). For example: how to size a cable

: 3% for power, 5% total including distribution. Example : 2

| 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. | Voltage drop reduces torque in motors, causes flicker

Example : Isc = 3 kA, t = 0.1 s (breaker trip), Cu/XLPE, k=143. $S_min = \sqrt(3000^2 × 0.1) / 143 = \sqrt900,000 / 143 = 948 / 143 = 6.6 mm²$. Minimum = 6.6 → choose 10 mm² (next standard size).

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