Voltage Drop Calculator
How to Calculate Voltage Drop
Voltage Drop Formulas
Single Phase: Vd = 2 × L × I × R / 1000
Three Phase: Vd = 1.732 × L × I × R / 1000
Where:
- Vd = Voltage drop (volts)
- L = Wire length (feet)
- I = Current (amperes)
- R = Resistance (ohms per 1000 ft)
National Electrical Code (NEC) Recommendations
- Branch Circuits: Maximum 3% voltage drop
- Feeders: Maximum 3% voltage drop
- Total (Branch + Feeder): Maximum 5% voltage drop
Example Calculation
A 120V single-phase circuit with 15A load, 100ft of 12 AWG copper wire:
- Resistance of 12 AWG copper: 1.93 ohms/1000ft
- Vd = 2 × 100 × 15 × 1.93 / 1000 = 5.79V
- Percentage = 5.79 / 120 × 100 = 4.83%
Frequently Asked Questions
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