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Entered R and XNo conductor selection

Voltage Drop
Calculator

Calculate effective-impedance voltage drop using values verified for the exact conductor and installation.

Embedded NEC table values removed
The former page silently assumed one NEC edition, PVC raceway, 75°C, 60 Hz, and conductor table. Enter values from the adopted source and exact installation instead.

Who it's for: electrical engineers and contractors calculating voltage drop at construction documents from verified conductor impedance.

Voltage-drop arithmetic
matching Ω/1,000-length values

How to use this calculator

1
Verify the circuit method
Select the adopted calculation basis and exact conductor/installation before taking R and X values.
2
Enter matching impedance and length units
R and X are per 1,000 of the same unit used for the one-way length.
3
Enter operating quantities
Use the evaluated current, system voltage, phase, and lagging power factor for the same condition.
4
Compare separately
Apply any project, equipment, utility, or adopted-code criterion outside this arithmetic.

The formula

Zeff = R × PF + X × √(1 − PF²). Voltage drop = k × I × Zeff × length/1,000, where k = 2 for single phase and √3 for three phase. Drop % = drop/system voltage × 100.

Worked example

Example
R 1.2 and X 0.05 Ω/1,000 ft, 100 ft, 20 A, 240 V single phase, and PF 0.90 produce approximately 1.84% drop.

When this estimate will be off

  • No conductor, cable, raceway, temperature, frequency, or impedance value is selected.
  • Does not calculate ampacity, load, conductor size, neutral effects, harmonics, starting conditions, or feeder/branch allocation.
  • Does not embed or enforce a universal percentage criterion.
  • The result is arithmetic from entered values, not compliance or conductor adequacy.

Frequently asked questions

A common mistake: No conductor, cable, raceway, temperature, frequency, or impedance value is selected.

A built-in table silently fixes edition, conductor construction, material, temperature, raceway, and frequency. Requiring entered verified impedance keeps those choices explicit.

Sources

  • User-selected adopted conductor/impedance source — must supply R and X for the exact installation and edition
  • Project and equipment criteria — must supply any acceptable voltage-drop limit

This free Voltage Drop Calculator is built and maintained by DataDrivenAEC, using the relevant codes and standards. It does not substitute for professional judgment.