What is Voltage Drop?
Voltage drop is the reduction in voltage that occurs as electrical current flows through the resistance of conductors. While ampacity ensures wires don't overheat, voltage drop affects performance and efficiency.
Why Voltage Drop Matters
Understanding voltage drop is critical for proper electrical system design:
- Equipment Performance: Motors may not start or run properly
- Light Quality: Lamps operate dimmer than rated
- Energy Efficiency: Wasted power dissipated as heat
- Appliance Lifespan: Low voltage can damage electronics
NEC Voltage Drop Standards
The NEC provides recommendations (not mandatory requirements) for voltage drop:
- Branch Circuits: Maximum 3% voltage drop
- Feeders: Maximum 2% voltage drop
- Combined (Feeder + Branch): Maximum 5% total
Calculating Voltage Drop
Use the standard voltage drop formula to calculate expected drop in your circuits.
NEC Recommendations
While not mandatory under the NEC, these limits are considered best practice and industry standard. They are often enforced by local codes and inspectors.
Practical Wire Sizing Guidelines
When to upsize wire for voltage drop:
- Under 50 feet: Standard ampacity sizing usually sufficient
- 50-100 feet: Check voltage drop, may need to upsize 1 gauge
- 100-150 feet: Likely need to upsize 1-2 gauges
- Over 150 feet: Calculate voltage drop, may need 2-3 gauge upsize
Voltage Drop Mitigation Strategies
Several strategies can help reduce voltage drop in your electrical installations.
Important
Voltage drop exceeding 3% can cause equipment malfunction and inefficient operation. Always calculate and verify before installation.
Conclusion
While the NEC voltage drop limits are recommendations rather than strict requirements, following them is essential for proper equipment operation, energy efficiency, and professional installations. Always calculate voltage drop for circuits over 50 feet, and don't hesitate to upsize wire when needed.
Use our Voltage Drop Calculator to quickly determine if your wire size is adequate.