Wire & Cable Voltage Drop Calculator – Essential Guide
Voltage drop is the reduction in voltage caused by the resistance of conductors when current flows. Excessive drop leads to inefficient operation, overheating, and equipment failure. The NEC recommends a maximum 3% drop for branch circuits and 5% total (feeder + branch). Our calculator uses fundamental Ohm’s law: Vd = 2 × I × R × L for DC/single‑phase (round trip) and Vd = √3 × I × R × L for three‑phase. For example, a 120V heater drawing 10A over 100ft of 10 AWG copper (R=0.999Ω/kft) gives Vd ≈ 2×10×0.999×0.1 = 1.998V, drop% = 1.665%, final voltage ≈ 118V, power loss ≈ 20W. Aluminum has higher resistance; increase gauge if drop exceeds 3%. This tool supports bulk design for solar farms, EV chargers, or industrial panels. Upload CSV and export results instantly.