Example: 5000 A fault, 0.1 sec clearing, XLPE copper → S ≥ √(5000² × 0.1) / 143 = √2,500,000 / 143 = 1581 / 143 ≈ → already satisfied by 16 mm².

The voltage drop should typically not exceed 3% for lighting circuits or 5% for power circuits. If the calculated drop is too high, you must select the next larger cable size.

Where:

Try 16 mm²: Vd per km ≈ 2.4 V/A/km Vd = 2.4 × 51 × 0.15 = 18.4 V → 4.6% → .

| mm² | Ampacity (A) | |-----|---------------| | 1.5 | 19 | | 2.5 | 27 | | 4 | 36 | | 6 | 46 | | 10 | 63 | | 16 | 85 | | 25 | 115 |