Voltage Drop Chart per AWG (20 A, 100 ft, 120 V)
Voltage drop by conductor size at 20 amps over a 100-foot one-way run on a 120 V single-phase copper circuit — a quick reference for the 3% guideline.
| AWG | Voltage Drop | Drop % |
|---|---|---|
| 14 AWG | 12.56 V | 10.5 % |
| 12 AWG | 7.90 V | 6.6 % |
| 10 AWG | 4.97 V | 4.1 % |
| 8 AWG | 3.13 V | 2.6 % |
| 6 AWG | 1.97 V | 1.6 % |
| 4 AWG | 1.24 V | 1.0 % |
| 3 AWG | 0.98 V | 0.8 % |
| 2 AWG | 0.78 V | 0.6 % |
| 1 AWG | 0.62 V | 0.5 % |
| 1/0 AWG | 0.49 V | 0.4 % |
| 2/0 AWG | 0.39 V | 0.3 % |
| 3/0 AWG | 0.31 V | 0.3 % |
| 4/0 AWG | 0.24 V | 0.2 % |
Sources: NEC Chapter 9 Table 8 (conductor resistance), NEC 310.16 (ampacity), NEC Chapter 9 Tables 1/4/5 (conduit areas & THHN), ASTM B258 (AWG geometry), NREL (peak sun hours) · All sources