Calculate Cable Sizes | How To

References: IEC 60364-5-52, BS 7671 (UK), NEC Article 310 (US), AS/NZS 3008 (Australia).

Voltage drop. For 2.5 mm² copper, ( R_ac ≈ 8.91 \text Ω/km ). Single phase drop = ( \frac2 \times 40 \times 21.74 \times 8.911000 = 15.5V ). 15.5V / 230V = 6.7% → exceeds 3% limit (6.9V max).

From IEC table – 2.5 mm² copper carries 24 A. Derating: ( C_t = 0.94 ) (35°C). ( I_z = 24 \times 0.94 = 22.56 A ) – adequate.

Where ( I_z ) = derated cable ampacity. Load: 5 kW heater, 230V AC, power factor = 1. ( I_b = 5000 / 230 = 21.74 A )

[ I_b \leq I_n \leq I_z ]

[ I_z \geq I_b ]