Calculation - For Cable Size

Short-circuit check: I_sc = 10 kA, t=0.1s, k=143 [ S_{min} = \frac{\sqrt{10000^2 \times 0.1}}{143} = \frac{3162}{143} \approx 22.1\ \text{mm}^2 ] 35 mm² > 22.1 mm² → OK.

From cable table – 35 mm² Cu/PVC (ampacity ≈ 135 A) selected. calculation for cable size

Voltage drop (assuming R=0.524 Ω/km, X=0.078 Ω/km for 35 mm²): [ V_d = \frac{1.732 \times 120 \times 94.3 \times (0.524\times0.85 + 0.078\times0.527)}{1000} \approx 9.5\ \text{V} ] 9.5V / 400V = 2.37% (<3%) → Acceptable. Short-circuit check: I_sc = 10 kA, t=0

[ I_b = \frac{50,000}{\sqrt{3} \times 400 \times 0.85 \times 0.9} \approx 94.3\ \text{A} ] Short-circuit check: I_sc = 10 kA

Correction factors (from tables): Cₜ (40°C) = 0.87, C₉ (1 circuit) = 1.0, Cₛ (buried, thermal resistivity 2.5 K·m/W) = 0.85 [ \text{Required ampacity} = \frac{94.3}{0.87 \times 0.85} \approx 127.5\ \text{A} ]