Calculate temperature-adjusted wire capacity
Wire ampacity is the maximum current a conductor can carry continuously without exceeding its temperature rating. The NEC requires adjustments for temperature and conductor bundling.
What is Ampacity? The current-carrying capacity of a wire, measured in amperes (amps). Exceeding ampacity causes dangerous overheating.
NEC Ampacity Tables: Base ampacities are found in NEC Table 310.15(B)(16). These assume 30°C (86°F) ambient temperature and up to 3 current-carrying conductors.
| Wire Size | Ampacity | Common Use |
|---|---|---|
| 14 AWG | 15A | Lighting circuits |
| 12 AWG | 20A | General outlets |
| 10 AWG | 30A | Dryers, water heaters |
| 8 AWG | 40A | Electric ranges |
| 6 AWG | 55A | Large appliances |
| 4 AWG | 70A | Sub-panels |
| 2 AWG | 95A | Service feeders |
Temperature Correction: Higher ambient temperatures reduce ampacity. For each 5°C above 30°C, multiply base ampacity by correction factor (0.96 to 0.58).
Conductor Bundling: When more than 3 current-carrying
conductors share a raceway, heat builds up. Apply adjustment
factors:
• 4-6 conductors: 80%
• 7-9 conductors: 70%
• 10-20 conductors: 50%
Important notes:
• Neutral and ground wires don't count unless they carry current
• Both corrections apply together (multiply both factors)
• Aluminum carries ~80% current of equivalent copper
• Never exceed wire ampacity - fire hazard!
How to use: Select wire size, material, and insulation rating. Enter ambient temperature and number of conductors in conduit. Calculator applies NEC correction factors.