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Voltage Drop Percentage
Note: 14 AWG aluminum is not rated for branch circuit use per NEC Table 310.16.
⚠ Safety Notice:
All electrical work should be performed by or reviewed by a licensed electrician. This calculator provides estimates for informational purposes only.
Understanding Voltage Drop
Voltage drop is the reduction in voltage that occurs as electricity travels through a wire. All conductors have resistance, and that resistance causes some voltage to be "lost" as heat before reaching the load. The NEC recommends keeping voltage drop under 3% for branch circuits, and under 5% total for the entire circuit (feeder + branch).
VD = (K × M × L × I) ÷ CM VD% = (VD ÷ V) × 100
Where K = 12.9 for copper or 21.2 for aluminum, M = 2 for single-phase or √3 (1.732) for three-phase, L = one-way length in feet, I = current in amps, CM = circular mils of the wire. Excessive voltage drop causes lights to dim, motors to run hot and inefficiently, and electronics to malfunction.