Formulas used
- Single phase: Vd = 2 x I x L x rho / A
- Three phase: Vd = 1.732 x I x L x rho / A
- rho = 0.01724 ohm mm2/m (copper), 0.02826 (aluminium), at 20 C
Frequently asked questions
What voltage drop is allowed?
Many designs aim for 3% on lighting circuits and 5% overall from the supply point to the load. Check the rules that apply to your installation.
Does this include reactance?
No. It uses conductor resistance only, which is accurate for small and medium cables. Very large cables have noticeable reactance, so the real drop will be slightly higher.