Cable Voltage Drop Calculator
Calculate voltage drop in electrical cables based on length, current, and wire gauge.
Get recommendations for meeting NEC and IEC standards.
Voltage Drop Analysis
Voltage drop occurs when current flows through cable resistance over distance. Excessive drop causes equipment malfunction and energy waste.
Imperial formula (single-phase):
Voltage Drop = (2 x Length (ft) x Current (A) x Resistance per ft) / 1000
Metric formula (single-phase):
Voltage Drop = (2 x Length (m) x Current (A) x Resistance per m) / 1000
NEC/IEC recommendations:
- Branch circuits: max 3% voltage drop
- Feeder + branch combined: max 5% voltage drop
- Critical loads: max 2% voltage drop
Copper wire resistance (ohms per 1000 ft / per km):
- 14 AWG (2.5 mm²): 3.14 / 7.41
- 12 AWG (4.0 mm²): 1.98 / 4.61
- 10 AWG (6.0 mm²): 1.24 / 3.08
- 8 AWG (10 mm²): 0.778 / 1.93
- 6 AWG (16 mm²): 0.491 / 1.21
- 4 AWG (25 mm²): 0.308 / 0.77
- 2 AWG (35 mm²): 0.194 / 0.49
The factor of 2 accounts for the round-trip distance (hot and neutral/return conductors).