Understanding Wire Ampacity
Ampacity is the maximum current a conductor can carry continuously under specific conditions without exceeding its temperature rating. This comprehensive chart provides ampacity values for common wire sizes based on NEC standards.
Copper Wire Ampacity Chart (75°C)
| AWG Size | 60°C | 75°C | 90°C | Common Use |
|---|---|---|---|---|
| 14 AWG | 15A | 20A | 25A | Lighting circuits |
| 12 AWG | 20A | 25A | 30A | General outlets |
| 10 AWG | 30A | 35A | 40A | Large appliances |
| 8 AWG | 40A | 50A | 55A | Electric ranges |
| 6 AWG | 55A | 65A | 75A | Large equipment |
| 4 AWG | 70A | 85A | 95A | Service feeders |
| 2 AWG | 95A | 115A | 130A | Main panels |
Temperature Rating Explained
- 60°C (140°F): Basic insulation, older installations
- 75°C (167°F): Most common for residential wiring (THHN, THWN)
- 90°C (194°F): High-temperature applications (THHN in dry locations)
Aluminum Wire Ampacity
Aluminum conductors have lower ampacity than copper. For the same current rating, aluminum requires approximately 2 AWG sizes larger than copper.
Derating Factors
Base ampacity values must be adjusted for:
- Ambient Temperature: Higher temperatures reduce ampacity
- Conductor Bundling: Multiple conductors generate more heat
- Installation Method: Conduit vs. free air affects heat dissipation
Practical Applications
Use our Wire Ampacity Calculator to quickly determine the correct wire size for your specific application with automatic derating calculations.