About Voltage Drop Calculator
Voltage drop is the voltage lost across the resistance of a cable between the supply and the load. For DC and single-phase circuits this calculator uses Vd = 2 × I × ρ × L ÷ A, counting both conductors, and for three-phase Vd = √3 × I × ρ × L ÷ A. Resistivity ρ is 0.0172 Ω·mm²/m for copper and 0.0282 for aluminium at 20 °C. Cable reactance and temperature rise are ignored, so real drops are slightly higher.
How to use Voltage Drop Calculator
- Fill in "System", "Supply voltage", "Current" and "One-way cable length", and the other options.
- The result appears below and updates as you type.
- Copy the result with the copy button, or download it as a file where that is offered.
Questions about Voltage Drop Calculator
How much voltage drop is acceptable?
Many wiring rules recommend keeping the drop within about 3 percent for lighting or branch circuits and 5 percent overall. The exact limit depends on the electrical code that applies where the installation is, so check that code.
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