PVC-insulated copper, clipped to wall (method C), ambient 35°C, no grouping, length 40m.
[ I_z \geq I_b ]
References: IEC 60364-5-52, BS 7671 (UK), NEC Article 310 (US), AS/NZS 3008 (Australia). how to calculate cable sizes
Increase to 4 mm² (( R_ac ≈ 5.62 \text Ω/km )). Drop = ( 2 \times 40 \times 21.74 \times 5.62 / 1000 = 9.77V ) → 4.25% (still over). Increase to 6 mm² (( R_ac ≈ 3.71 )). Drop = ( 2 \times 40 \times 21.74 \times 3.71 / 1000 = 6.45V ) → 2.8% (acceptable). PVC-insulated copper, clipped to wall (method C), ambient
[ I_b \leq I_n \leq I_z ]