Trying a 300mm² cable (base rating ~ 520A): $520A \times 0.326 = 169.5A$ (Sufficient for 150A load).
We must select a larger base cable. Iterate until $I_actual > 150A$. cable rating and derating factor
$$I_actual = I_base \times K_1 \times K_2 \times K_3 \times K_4 \times K_5$$ Trying a 300mm² cable (base rating ~ 520A): $520A \times 0
Trying a 240mm² cable (base rating ~ 450A): $450A \times 0.326 = 146.7A$ (Still slightly low). $$I_actual = I_base \times K_1 \times K_2 \times
At the heart of cable selection lies two critical concepts: (Ampacity) and Derating Factors .
12 current-carrying conductors in bundle: $K_group = 0.50$ (NEC 10-20 conductors)
Correction factors for buried cables: | Soil Resistivity (K·m/W) | Correction Factor | | :--- | :--- | | 0.7 (Wet, marsh) | 1.05 – 1.10 | | 1.0 (Moist loam) | 1.00 | | 1.5 (Dry sand) | 0.85 | | 2.0 (Very dry gravel) | 0.70 | | 3.0 (Thermal backfill required) | 0.50 |