Voltage Drop Calculator
Calculate voltage drop for electrical circuits per NEC recommendations. Determine if your wire size is adequate for the run distance and load, and find the minimum wire size to stay within code limits.
1.0 for resistive loads, 0.85 for motors
Results
Voltage Drop
7.92
volts
Voltage Drop %
3.30%
of source voltage
Voltage at Load
232.1V
delivered
Branch Circuit (3%)
FAIL
NEC recommends max 3%
Total Circuit (5%)
PASS
NEC recommends max 5% total
Power Loss
158.4
watts
Minimum Wire Size for Under 3% Drop
10 AWG Copper
How to Use This Calculator
Select the system voltage, phase, wire material, and wire gauge. Enter the one-way wire distance in feet and the load current in amps. Adjust the power factor if you are feeding motor loads (typically 0.85). The calculator shows the voltage drop, percentage, whether it passes NEC guidelines, and recommends the minimum wire size needed to keep voltage drop under 3%.
Formula Used
Single-phase: VD = 2 x I x R x L / 1000. Three-phase: VD = sqrt(3) x I x R x L / 1000. VD% = (VD / Source Voltage) x 100. NEC recommends max 3% for branch circuits, 5% total including feeder.
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Disclaimer
This calculator is for estimation purposes only. Results may vary based on local conditions, materials, and building codes. Always consult a licensed professional before making decisions based on these calculations. MyContractorTools is not responsible for any errors or omissions.