Wire voltage drop calculator

Understand the drop across your conductor run.

Compare distance, current and conductor electrical properties. Calculate the modeled voltage drop and the run length corresponding to your own drop target.

This tool evaluates voltage drop. It does not select an AWG size, establish ampacity or specify a breaker. It is free, needs no account and is an independent utility, not something you have to be an OrdexisOne customer to use.

Enter the circuit conditions.

Example values demonstrate the method; they do not represent a specified wire product. Replace them with assessed circuit data and manufacturer values.

Circuit & distance

Circuit type

Supply voltage V · across the two supply conductors

Load current A · per phase for three phase

Length & conductor units

One-way run length ft

Enter source-to-load distance once. The formula includes the return conductor for single-phase and DC circuits; three phase assumes a balanced load.

Conductor electrical properties

Use resistance per conductor at the expected operating temperature. For AC, use AC resistance and inductive reactance appropriate to the frequency and conductor arrangement. Material and temperature are represented by these entered values.

Conductor resistance, R Ω / 1,000 ft

Inductive reactance, X Ω / 1,000 ft

Lagging power factor greater than 0, up to 1

Your comparison target

Voltage-drop target % of supply voltage

The example 3% is an editable comparison target, not a determination of the limit for your installation.

Method & assumptions

Review the calculation before applying the result.

The circuit determines the multiplier.

DC, two conductors: Drop = 2 × I × R × L
Single-phase AC: Drop ≈ 2 × I × (R × PF + X × √(1 − PF²)) × L
Balanced three-phase AC: Drop ≈ √3 × I × (R × PF + X × √(1 − PF²)) × L

Here L is one-way length in thousands of feet or kilometres, matching R and X. I is conductor current. Percentage drop is drop ÷ supply voltage × 100.

Schneider Electric’s Electrical Installation Guide explains the AC equations.

Use the properties of the actual run.

The model assumes equal conductors and a concentrated load at the end of one run. Resistance must match the conductor’s operating conditions; the calculator does not apply a temperature correction. Connections and upstream voltage drop are excluded.

AC results exclude harmonics, leading power factor, unbalanced loads, motor starting and voltage regulation effects. At large percentage drops, the AC approximation becomes less useful. A calculated drop at or above supply voltage is flagged rather than shown as a usable load voltage.

Complete the conductor selection separately.

Installation method, conductor ratings, ambient conditions, grouping, terminations and overcurrent protection affect the final selection. Southwire’s voltage-drop tool includes conductor and installation options for further project-specific evaluation.

From the assessed work to the completed service.

See how OrdexisOne supports electrical service intake, project quotes, assigned visits and connected customer billing.

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