Wire Size for 20.78 Amps
Typical copper wire gauges for 20.78 amps across common run lengths on a 120V circuit, sized to keep voltage drop under 3% and respect the NEC 240.4(D) small-conductor rule. At 20.78A the load sits in residential-branch territory where aluminum is not a typical conductor, so the table lists copper only. Actual install sizing depends on conductor material, insulation/termination temperature rating, cable type, ambient and bundling derates, and local code.
20.78A Wire Gauge by Distance
| Distance | Copper Gauge | V-Drop (Cu) | NEC Status |
|---|---|---|---|
| 25 ft | 10 AWG | 1.29V (1.07%) | OK |
| 50 ft | 10 AWG | 2.58V (2.15%) | OK |
| 75 ft | 8 AWG | 2.43V (2.02%) | OK |
| 100 ft | 8 AWG | 3.23V (2.69%) | OK |
| 125 ft | 6 AWG | 2.55V (2.13%) | OK |
| 150 ft | 6 AWG | 3.06V (2.55%) | OK |
| 175 ft | 6 AWG | 3.57V (2.98%) | OK |
| 200 ft | 4 AWG | 2.56V (2.13%) | OK |
| 250 ft | 4 AWG | 3.2V (2.67%) | OK |
| 300 ft | 3 AWG | 3.05V (2.55%) | OK |
| 400 ft | 2 AWG | 3.23V (2.69%) | OK |
| 500 ft | 1 AWG | 3.2V (2.67%) | OK |
Copper gauges use the NEC 240.4(D) branch-circuit cap, not raw 75°C ampacity.
Also Calculate
Other Amperages
This calculator provides estimates for reference purposes only. Always consult a licensed electrician and verify compliance with the National Electrical Code (NEC) and local electrical codes before performing any electrical work.