Voltage Drop

Category: science

The gradual loss of electrical potential that occurs as current travels down a long run of wire due to conductor resistance.

Voltage drop is an efficiency bottleneck. The NEC recommends keeping voltage drop below 3% on branch circuits (NEC 210.19). If a 120V line runs 200 feet, internal copper resistance drops the voltage at the outlet, causing electric motors to run hot and computers to experience brownout resets.

Common Examples

• To counteract a severe 5% voltage drop on the long parking lot lighting run, the engineer up-sized the wire from 10 AWG to 6 AWG.
• Calculating voltage drop metrics requires modeling the circuit’s total distance, active amperage draw, and conductor material properties.