Wire Size for 120 Amps
Typical copper and aluminum wire gauges for 120 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. Actual install sizing depends on conductor material, insulation/termination temperature rating, cable type, ambient and bundling derates, and local code.
120A Wire Gauge by Distance
| Distance | Copper Gauge | Aluminum Gauge | V-Drop (Cu) | NEC Status |
|---|---|---|---|---|
| 25 ft | 1 AWG | 1/0 AWG | 0.924V (0.77%) | OK |
| 50 ft | 1 AWG | 1/0 AWG | 1.85V (1.54%) | OK |
| 75 ft | 1 AWG | 1/0 AWG | 2.77V (2.31%) | OK |
| 100 ft | 1/0 AWG | 2/0 AWG | 2.93V (2.44%) | OK |
| 125 ft | 2/0 AWG | 3/0 AWG | 2.9V (2.42%) | OK |
| 150 ft | 2/0 AWG | 4/0 AWG | 3.48V (2.9%) | OK |
| 175 ft | 3/0 AWG | 4/0 AWG | 3.22V (2.68%) | OK |
| 200 ft | 4/0 AWG | 300 kcmil | 2.92V (2.43%) | OK |
| 250 ft | 250 kcmil | 500 kcmil | 3.09V (2.57%) | OK |
| 300 ft | 300 kcmil | 500 kcmil | 3.09V (2.57%) | OK |
| 400 ft | 350 kcmil | 750 kcmil | 3.52V (2.94%) | OK |
| 500 ft | 500 kcmil | 750 kcmil | 3.1V (2.58%) | OK |
Aluminum is not typical for 10 AWG and smaller branch-circuit conductors in residential settings. 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.