Voltage drop maximum distance calculator

Preliminary estimate

Inputs

Calculation note

This rearranges the voltage-drop formula for length. It does not set the allowed drop, choose a conductor, or approve a circuit.

Method

Allowed volts = nominal volts x allowed drop percent / 100

Three-phase length = allowed volts x area / (sqrt(3) x resistivity x amps)

Single-phase or DC length = allowed volts x area / (2 x resistivity x amps)

MoreLess

Formula variables

  • Nominal voltage sets the allowed volts dropped.
  • Current is the design or measured current used in the voltage-drop screen.
  • Conductor area is entered in mm2.
  • The result is maximum one-way length before project criteria and product data are applied.

Assumptions

  • The calculator rearranges the voltage-drop formula to solve for one-way length.
  • Conductor area is entered directly in square millimetres.
  • Copper and aluminum resistivity values match the site voltage-drop calculators.
  • This calculator does not choose conductor size, set an acceptable voltage-drop limit, or approve installation design.

Examples

600 V feeder screen. A 100 A three-phase load at 600 V with 3 percent drop and 53.5 mm2 copper estimates about 322.5 m one-way.

Conductor workflow. Use conductor tables for area context, then run the full voltage-drop calculator for project-specific conductor labels.