Voltage Drop Calculator | Free Construction Calculators

Calculate voltage drop for electrical wire runs to ensure proper circuit performance and NEC compliance. Our professional voltage drop calculator helps electricians, contractors, and engineers determine voltage loss across conductor distances for copper and aluminum wire. Enter amperage, wire size (AWG), and run length at 120V, 240V, or 480V to verify voltage drop stays within NEC recommended 3% for branch circuits and 2% for feeders.

Excessive voltage drop causes motors to overheat, lights to dim, appliances to malfunction, and equipment to fail prematurely. The National Electrical Code recommends limiting voltage drop to 3% maximum on branch circuits and 2% on feeders (5% total combined) to maintain proper equipment operation and energy efficiency. Long wire runs, undersized conductors, or high current loads can exceed these limits, requiring larger wire gauge to reduce resistance and minimize voltage loss. Our calculator instantly determines actual voltage drop percentage and recommends proper wire sizing to meet NEC guidelines for residential, commercial, and industrial installations.

Whether you're running power to a detached garage, installing a subpanel, sizing conductors for an EV charger, or troubleshooting dimming lights, accurate voltage drop calculations ensure proper circuit design. Voltage drop is particularly critical for motor loads (well pumps, HVAC compressors, power tools) which experience reduced torque and overheating when voltage falls below nameplate ratings. Understanding the relationship between wire resistance, conductor length, and current flow allows electricians to select appropriate wire sizes that maintain voltage within acceptable limits while minimizing material costs and installation complexity.