Voltage Drop Calculator
Wire-run voltage drop from AWG, length, current, and source voltage (NEC Table 9).
How to Use
- Enter amps, one-way distance, wire gauge, and source voltage.
- Rule: keep drop ≤ 3% for branch, ≤ 5% total.
Input
Result
Formula
Single-phase
Vd = 2 × L × R × I / 1000 (R in Ω per 1000 ft)
Three-phase
Vd = √3 × L × R × I / 1000
NEC rule-of-thumb
≤ 3% branch · ≤ 5% feeder+branch combined
Last updated: