WireWicket / Field calculation 02

Single- and three-phase voltage drop

Estimate voltage drop from phase, system voltage, load, one-way run length, conductor material, and conductor size. The example values are a starting fixture, not a recommendation.

Calculation inputs

Single-phase run

Enter a finite voltage greater than 0 V.

Enter a finite load current of 0 A or greater.

Enter a finite one-way length of 0 ft or greater.

Single-phase mode estimates a two-conductor run using the selected material and conductor size.

Single-phase result

Single-phase · 120 V · 20 A · 100 ft one way · Copper · 12 AWG
Voltage drop
7.90 V
Voltage drop percentage
6.58%

Voltage drop ÷ system voltage × 100

Calculation inputs
120 V system · 20 A · 100 ft one way · Copper · 12 AWG (6,530 CM)

Calculation basis

Resistance-only estimate at 75°C using Vdrop = 2 × K × I × L ÷ CM. K = 12.9 for Copper; I is load current in amperes, L is one-way length in feet, and CM is conductor area in circular mils.

This estimate does not model conductor reactance, load power factor, or temperature changes.

Source: NCCER Electrical Formula Sheet