Calculate conductor resistance from material, length and cross-sectional area.
Resistance rises with length and falls with area. Copper resistance increases about 0.39 per cent per kelvin, so a conductor at its 70 °C rating has roughly 20 per cent more resistance than at 20 °C — which matters for both voltage drop and fault calculations. Loop resistance is twice the one-way value because current must return, and it is the loop figure that determines voltage drop and earth fault current.
Cable Resistance
R = ρ L ÷ A, with ρ corrected for temperature as ρ₂₀(1 + α ΔT)
R = ρ L ÷ A, with ρ corrected for temperature as ρ₂₀(1 + α ΔT) Resistance rises with length and falls with area. Copper resistance increases about 0.39 per cent per kelvin, so a conductor at its 70 °C rating has roughly 20 per cent more resistance than at 20 °C — which matters for both voltage drop and fault calculations.
Loop resistance is twice the one-way value because current must return, and it is the loop figure that determines voltage drop and earth fault current.
This calculator takes 4 inputs: Cable length one way, Conductor cross-sectional area, Conductor material, Conductor temperature. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.