Cable size calculator
Select the smallest copper cable that meets both ampacity and voltage-drop limits per SANS 10142-1 / IEC 60364, with installation-method and ambient-temperature derating.
Design current
25.5A
= 31.8 A with 25 % margin
Suggested breaker
32A
3-pole MCB / MCCB · 400 V system.
Minimum cable size
6mm² copper
= 2.55 % Vd over 50 m
Driven by ampacity, not voltage drop (voltage drop alone needs only 4 mm²).
Derated ampacity at chosen size
33.8A
After 100 % install × 94 % ambient.
Cable specification
For a 15 kW load over a 50 m run on a 400 V three-phase system, install 6 mm² copper (PVC, 70 °C) protected by a 32 A breaker. Voltage drop at full load = 2.55 % (limit 5 %). Derated ampacity at this size = 33.8 A.
Driven by ampacity, not voltage drop (voltage drop alone needs only 4 mm²).