IEC 60364 requires (R) be calculated at the , not at 20°C. The standard assumes maximum normal operating temperature (e.g., 70°C for PVC, 90°C for XLPE).
Where:
Example: A 3-phase 400V circuit, 100m, 50A, cosφ=0.8, using 16mm² copper (say ~2.8 mV/A/m): [ \Delta U = 50 \cdot 100 \cdot 2.8 / 1000 = 14 \text V ] Relative drop = (14 / 400 = 3.5%). iec 60364 cable sizing voltage drop formula
Resistance at temperature (t): [ R_t = R_20 \cdot [1 + \alpha_20 (t - 20)] ] Where (\alpha_20) ≈ 0.00393 /K for copper, 0.00403 /K for aluminum. IEC 60364 requires (R) be calculated at the , not at 20°C
The IEC 60364 standard sets permissible voltage drop limits for different types of electrical installations: 70°C for PVC