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
Based on NEC Table 310.16 for not more than 3 current-carrying conductors in raceway or cable:
- 14 AWG: 15A at all temperature ratings
- 12 AWG: 20A at all temperature ratings
- 10 AWG: 30A at all temperature ratings
- 8 AWG: 40-55A depending on insulation temperature
Aluminum Wire Ampacity
Aluminum requires larger wire for the same current. Based on NEC Table 310.16:
- 12 AWG Aluminum: 15A at all temperature ratings
- 10 AWG Aluminum: 25A at all temperature ratings
- 8 AWG Aluminum: 35-45A depending on insulation temperature
Understanding Insulation Types
Different insulation types allow different operating temperatures.
Temperature Rating Guide
60°C (TW, UF): Basic insulation. 75°C (THW, THWN): Most common. 90°C (THHN, XHHW): Best performance.
How to Use This Chart
Follow these steps to determine wire ampacity:
- 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)
Special Considerations
Always check the temperature rating of equipment where wire terminates. Use the lower of wire or terminal ratings for ampacity selection.
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.
Related Tools
Use our tools for accurate ampacity calculations and wire sizing for your specific project requirements.
Use our Ampacity Calculator to calculate with derating factors.