From IEC table for XLPE/Cu, 10 mm² → ~70 A. Select 10 mm².
Mechanical strength satisfied (≥1.5 mm²). how to size cable
VD (R = 2.2 Ω/km, X=0.09 Ω/km, cosφ=0.85, sinφ=0.527): [ V_d = \frac\sqrt3 \cdot 100 \cdot 56.6 \cdot (2.2\cdot0.85 + 0.09\cdot0.527)1000 \approx 18.4 \text V ] As % of 400V = 4.6% → exceeds 3% limit. Increase to 16 mm² (R=1.38 Ω/km). VD = 11.7 V → 2.9% OK. From IEC table for XLPE/Cu, 10 mm² → ~70 A