Calculate voltage drop per NEC for single-phase and three-phase circuits. Copper and aluminum, AWG 14 through 2000 kcmil, with pass/fail status and the full formula showing your work.
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Enter one-way length and load current to see voltage drop results.
NEC 210.19(A) Informational Note No. 4 recommends no more than 3% voltage drop on branch circuits and 5% total (feeder + branch) from the service entrance to the furthest outlet. These are recommendations, not Code requirements — but most AHJs and engineers treat them as de facto standards.
Copper (K=12.9) has lower resistivity than aluminum (K=21.2), meaning less voltage drop for the same wire size. Aluminum requires approximately two sizes larger than copper for equivalent performance. Aluminum is common for feeders and service entrances where the cost savings outweigh the larger conduit.
Long runs to outbuildings, well pumps, and EV chargers are the most common voltage drop problems. A 200-foot run to a 50A EV charger on 6 AWG copper at 240V drops 9.85V (4.1%) — marginal. Upgrading to 4 AWG brings it to 6.19V (2.6%). Motors are especially sensitive because low voltage increases current draw and heat.
NEC 2026 restructured Article 220 into the new Article 120, changed general lighting from 3 VA/sq ft to 2 VA/sq ft, and introduced new EV charging provisions. The voltage drop formula and conductor resistance values in Chapter 9 Table 8 remain unchanged — this calculator is current through NEC 2026.