Understanding Wire Ampacity
Ampacity is the maximum current a wire can safely carry without exceeding its temperature rating. This chart provides NEC-compliant ampacity values for copper and aluminum conductors at different temperature ratings.
Copper Wire Ampacity Chart
Based on NEC Table 310.16 for not more than 3 current-carrying conductors in raceway or cable:
| AWG | 60°C (TW, UF) | 75°C (THW, THWN) | 90°C (THHN, XHHW) |
|---|---|---|---|
| 14 | 15A | 15A | 15A |
| 12 | 20A | 20A | 20A |
| 10 | 30A | 30A | 30A |
| 8 | 40A | 50A | 55A |
| 6 | 55A | 65A | 75A |
| 4 | 70A | 85A | 95A |
| 3 | 85A | 100A | 115A |
| 2 | 95A | 115A | 130A |
| 1 | 110A | 130A | 145A |
| 1/0 | 125A | 150A | 170A |
| 2/0 | 145A | 175A | 195A |
| 3/0 | 165A | 200A | 225A |
| 4/0 | 195A | 230A | 260A |
Aluminum Wire Ampacity Chart
Aluminum requires larger wire for the same current. Based on NEC Table 310.16:
| AWG | 60°C | 75°C | 90°C |
|---|---|---|---|
| 12 | 15A | 15A | 15A |
| 10 | 25A | 25A | 25A |
| 8 | 35A | 40A | 45A |
| 6 | 40A | 50A | 55A |
| 4 | 55A | 65A | 75A |
| 2 | 75A | 90A | 100A |
| 1/0 | 100A | 120A | 135A |
| 2/0 | 115A | 135A | 150A |
| 4/0 | 150A | 180A | 205A |
Understanding Insulation Types
60°C Insulation (TW, UF)
- Lowest temperature rating
- TW: Thermoplastic, dry locations
- UF: Underground feeder, direct burial
- Limited use in modern installations
75°C Insulation (THW, THWN)
- Most common for general wiring
- THW: Thermoplastic, heat resistant, wet locations
- THWN: Same as THW with nylon jacket
- Standard rating for most terminations
90°C Insulation (THHN, XHHW)
- Highest common temperature rating
- THHN: Heat resistant, nylon jacket
- XHHW: Cross-linked polyethylene
- Best for derating calculations
Important
Even when using 90°C rated wire, you must use the 75°C ampacity column if the termination (breaker, outlet, switch) is only rated for 75°C. Most residential equipment is 75°C rated.
How to Use This Chart
- Determine your circuit's current requirement
- Identify your wire's insulation type and temperature rating
- Find the ampacity for your wire size in the appropriate column
- Apply derating factors if needed (temperature, bundling)
- Verify the derated ampacity exceeds your load requirement
Special Considerations
Terminal Temperature Ratings
Always check the temperature rating of the equipment where wire terminates. Use the lower of wire or terminal ratings for ampacity selection.
Continuous Loads
For continuous loads (3+ hours), limit current to 80% of ampacity, or size conductor for 125% of load.
Related Tools
- Ampacity Calculator - Calculate with derating factors
- Wire Gauge Calculator - Size wire for your project
- AWG Reference Chart - Complete wire specifications