What Size Wire for a 100 Amp Service?
For a 100 A single-phase dwelling service, the NEC allows 4 AWG copper or 2 AWG aluminum (310.12 83% rule). A general 100 A feeder sized from Table 310.16 needs 3 AWG copper / 1 AWG aluminum.
Minimum wire size for 100 amps
| Application | Copper (75°C) | Aluminum (75°C) |
|---|---|---|
| Branch circuit / feeder (Table 310.16) | 3 AWG | 1 AWG |
| Dwelling service / main feeder (310.12) | 4 AWG | 2 AWG |
Assumes 75°C-rated terminations (NEC 110.14(C)) and no more than three current-carrying conductors in a raceway at 30°C ambient. Derating, continuous loads, and local amendments can change the answer — confirm with a licensed electrician.
How far can you run it? (voltage drop)
Keeping voltage drop under the recommended 3% at a 80 A load (80% of the breaker), 3 AWG copper is good for roughly:
| System voltage | Max one-way run (3 AWG Cu) |
|---|---|
| 240 V | ≈ 183 ft |
Past these distances, step up one gauge. Run your exact length and load through the voltage drop calculator.
What runs on 100 amps
- Main service (older/smaller homes)
- Detached garage / ADU subpanel
Frequently asked questions
For a 100 A single-phase dwelling service or main feeder, the NEC 310.12 rule allows 4 AWG copper or 2 AWG aluminum. A general (non-dwelling-service) 100 A feeder sized from Table 310.16 needs 3 AWG copper or 1 AWG aluminum at 75°C.
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