How it works
Voltage drop arises across the resistance of the conductors. In a single-phase circuit the current flows out and back, so twice the length is used; in a balanced three-phase system the factor is √3, relative to the line-to-line voltage.
Formula
1~: ΔU = 2 · L · I · ρ · cos φ / A 3~: ΔU = √3 · L · I · ρ · cos φ / A ρ(T) = ρ20 · (1 + α · (T − 20))
The calculation neglects cable reactance, which is a good approximation below about 25–35 mm². At operating temperature resistance is higher: about 20% more for copper at 70 °C. The cross-section must also be checked for current capacity and protection.
All calculations run in your browser; your inputs never reach us.