Voltage Drop Calculator
Calculate voltage drop and final voltage at the load. Essential for sizing generator cords and long cable runs to prevent equipment damage.
Circuit Parameters
Results
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%
Voltage Drop
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Voltage Drop
-- V
Voltage at Load
-- V
The Math Behind the Numbers
Single-Phase Formula
VD = (2 × K × I × L) / CM
- VD: Voltage Drop (Volts)
- K: Material Resistivity (12.9 for Copper, 21.2 for Aluminum)
- I: Load Current (Amps)
- L: One-way Length (Feet)
- CM: Circular Mils (Wire Area)
Three-Phase Formula
VD = (1.732 × K × I × L) / CM
Three-phase circuits are more efficient, resulting in less voltage drop for the same load and distance compared to single-phase.
Quick Reference: Max Distance for 3% Drop (at 240V)
| Wire Gauge (Copper) | 20 Amps | 30 Amps | 50 Amps | 100 Amps |
|---|---|---|---|---|
| 12 AWG | 91 ft | - | - | - |
| 10 AWG | 144 ft | 96 ft | - | - |
| 8 AWG | 230 ft | 153 ft | - | - |
| 6 AWG | 366 ft | 244 ft | 146 ft | - |
| 4 AWG | 582 ft | 388 ft | 233 ft | 116 ft |
Based on Single-Phase, 240V, Copper wire. Distances are approximate.
Safety Note
This calculator aims for a maximum voltage drop of 3% to protect sensitive electronics. Always consult a qualified electrician and local codes (NEC) before installation. Aluminum wire must be sized larger than copper for the same load.