Cable - Sizing Calculations

I~load~ = (30,000) / (√3 × 400 × 0.9 × 0.85) = 56.6 A Step 2: I~d~ = 56.6 × 1.15 = 65 A Step 3: Derating: Temp (0.85) × Grouping (0.6) = 0.51. Need corrected ampacity ≥ 65 A → Table value needed = 65/0.51 = 127 A Step 4: Table for Cu/PVC gives 25 mm² (~140 A). Tentatively select 25 mm². Step 5: Voltage drop (R ≈ 0.727 Ω/km, X ≈ 0.08 Ω/km): VD = √3 × 0.15 × 56.6 × (0.727×0.85 + 0.08×0.526) ≈ 9.8 V. 9.8V / 400V = 2.45% (acceptable). Step 6: Short-circuit: I~sc~ = 5000 A, t=0.1 s, k=115. S = 5000×√0.1 / 115 = 5000×0.316/115 ≈ 13.7 mm² → 25 mm² is fine. Result: 25 mm² Copper/PVC is adequate. Quick Sizing Rules of Thumb (for initial estimates) | Load Current | Copper (PVC) | Copper (XLPE) | Aluminum (PVC) | |--------------|--------------|---------------|----------------| | 20 A | 2.5 mm² | 2.5 mm² | 4 mm² | | 32 A | 6 mm² | 4 mm² | 10 mm² | | 50 A | 16 mm² | 10 mm² | 25 mm² | | 80 A | 35 mm² | 25 mm² | 50 mm² | | 100 A | 50 mm² | 35 mm² | 70 mm² |

Typical growth factor: 0.1 to 0.25 (10-25%) A cable in hot ambient air or bundled with others cannot carry its rated current. cable sizing calculations

Engineers often say: "If you oversize a cable, you waste money. If you undersize it, you risk fire, voltage drops, and equipment failure." I~load~ = (30,000) / (√3 × 400 × 0