Everything about a 50 ft one-way run on one page: at 240 V and a 3% budget, a 20 A load needs 14 AWG copper and a 50 A load needs 8 AWG copper. The quick-answer table and the full percent-drop matrices are below.
| Load | 120 V copper | 240 V copper | 240 V aluminum |
|---|---|---|---|
| 15 A | 12 AWG | 14 AWG | 12 AWG |
| 20 A | 10 AWG | 14 AWG | 12 AWG |
| 30 A | 8 AWG | 10 AWG | 10 AWG |
| 40 A | 8 AWG | 8 AWG | 8 AWG |
| 50 A | 6 AWG | 8 AWG | 6 AWG |
| 60 A | 6 AWG | 6 AWG | 4 AWG |
| 80 A | 4 AWG | 4 AWG | 2 AWG |
| 100 A | 3 AWG | 3 AWG | 1 AWG |
| Copper \ Amps | 15 A | 20 A | 30 A | 40 A | 50 A | 60 A | 80 A | 100 A |
|---|---|---|---|---|---|---|---|---|
| 14 AWG | 3.8 | 5.1 | 7.7† | 10.2† | 12.8† | 15.4† | 20.5† | 25.6† |
| 12 AWG | 2.4 | 3.2 | 4.8† | 6.4† | 8.0† | 9.7† | 12.9† | 16.1† |
| 10 AWG | 1.5 | 2.0 | 3.0 | 4.0† | 5.0† | 6.0† | 8.1† | 10.1† |
| 8 AWG | 1.0 | 1.3 | 1.9 | 2.5 | 3.2 | 3.8† | 5.1† | 6.4† |
| 6 AWG | 0.6 | 0.8 | 1.2 | 1.6 | 2.0 | 2.5 | 3.3† | 4.1† |
| 4 AWG | 0.4 | 0.5 | 0.8 | 1.0 | 1.3 | 1.5 | 2.1 | 2.6† |
| 3 AWG | 0.3 | 0.4 | 0.6 | 0.8 | 1.0 | 1.2 | 1.6 | 2.0 |
| 2 AWG | 0.2 | 0.3 | 0.5 | 0.6 | 0.8 | 1.0 | 1.3 | 1.6 |
| 1 AWG | 0.2 | 0.3 | 0.4 | 0.5 | 0.6 | 0.8 | 1.0 | 1.3 |
| 1/0 AWG | 0.2 | 0.2 | 0.3 | 0.4 | 0.5 | 0.6 | 0.8 | 1.0 |
| 2/0 AWG | 0.1 | 0.2 | 0.2 | 0.3 | 0.4 | 0.5 | 0.6 | 0.8 |
| 3/0 AWG | 0.1 | 0.1 | 0.2 | 0.3 | 0.3 | 0.4 | 0.5 | 0.6 |
| 4/0 AWG | 0.1 | 0.1 | 0.2 | 0.2 | 0.3 | 0.3 | 0.4 | 0.5 |
| Copper \ Amps | 15 A | 20 A | 30 A | 40 A | 50 A | 60 A | 80 A | 100 A |
|---|---|---|---|---|---|---|---|---|
| 14 AWG | 1.9 | 2.6 | 3.8† | 5.1† | 6.4† | 7.7† | 10.2† | 12.8† |
| 12 AWG | 1.2 | 1.6 | 2.4† | 3.2† | 4.0† | 4.8† | 6.4† | 8.0† |
| 10 AWG | 0.8 | 1.0 | 1.5 | 2.0† | 2.5† | 3.0† | 4.0† | 5.0† |
| 8 AWG | 0.5 | 0.6 | 1.0 | 1.3 | 1.6 | 1.9† | 2.5† | 3.2† |
| 6 AWG | 0.3 | 0.4 | 0.6 | 0.8 | 1.0 | 1.2 | 1.6† | 2.0† |
| 4 AWG | 0.2 | 0.3 | 0.4 | 0.5 | 0.6 | 0.8 | 1.0 | 1.3† |
| 3 AWG | 0.2 | 0.2 | 0.3 | 0.4 | 0.5 | 0.6 | 0.8 | 1.0 |
| 2 AWG | 0.1 | 0.2 | 0.2 | 0.3 | 0.4 | 0.5 | 0.6 | 0.8 |
| 1 AWG | 0.1 | 0.1 | 0.2 | 0.3 | 0.3 | 0.4 | 0.5 | 0.6 |
| 1/0 AWG | 0.1 | 0.1 | 0.2 | 0.2 | 0.3 | 0.3 | 0.4 | 0.5 |
| 2/0 AWG | 0.1 | 0.1 | 0.1 | 0.2 | 0.2 | 0.2 | 0.3 | 0.4 |
| 3/0 AWG | 0.0 | 0.1 | 0.1 | 0.1 | 0.2 | 0.2 | 0.3 | 0.3 |
| 4/0 AWG | 0.0 | 0.1 | 0.1 | 0.1 | 0.1 | 0.2 | 0.2 | 0.3 |
Read across your load, down your gauge: ≤3.0 passes the NEC branch recommendation, ≤5.0 the total budget. Cells marked † exceed the 75 °C copper ampacity for that load — undersized regardless of drop. For aluminum multiply any value by ~1.61; for three-phase multiply by 0.866.
It depends on the load: at 240 V and 3%, 50 ft needs 14 AWG at 15 A, 14 AWG at 20 A, and 8 AWG at 50 A. At 120 V, sizes step up roughly two gauges — see the table above.
One-way — source to load. The return path is already in the formula (×2 single-phase, ×√3 three-phase), so don't double your measurement.