Voltage Drop Calculator
Calculate cable voltage drop for any wire gauge, length, current, and phase
Wire Gauge (AWG)
Wire Length (meters)
m
Load Current (Amperes)
A
Supply Voltage (V)
V
Phase
Voltage Drop Analysis
Voltage Drop
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Voltage at Load
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Drop Percentage
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Wire Resistance (Ω/km)
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Voltage Drop Explained
Voltage drop occurs when current flows through the resistance of a wire. NEC (National Electrical Code) recommends maximum 3% drop for branch circuits and 5% total (feeder + branch). Excessive voltage drop causes equipment to run hotter, reduces efficiency, and can damage motors.
For single-phase: VD = 2 × L × R × I (factor of 2 for live + neutral). For three-phase: VD = √3 × L × R × I. Use larger wire gauges for long runs or high-current loads. Going from 14 AWG to 12 AWG reduces resistance by ~37%.
lightbulb Example
12 AWG, 30m run, 20A, 230V single-phase:
1R = 5.21 Ω/km → 0.00521 × 30 × 2 × 20
2VD = 6.25 V (2.7%)
✓ Within 3% NEC limit