Cable Ampacity Calculator

Cable ampacity is the maximum current a conductor can carry continuously under specific conditions without exceeding its temperature rating. It's crucial for electrical safety and preventing fires caused by overheated conductors.

Higher ambient temperatures reduce a wire's current-carrying capacity because the conductor has less thermal headroom before reaching its insulation temperature limit. Correction factors are applied to derate the ampacity in hot environments.

Multiple conductors in the same raceway generate heat collectively, reducing each conductor's ability to dissipate heat. NEC requires derating factors when more than three current-carrying conductors share a raceway.

Aluminum conductors have lower ampacity ratings than copper for the same wire size due to higher electrical resistance. However, aluminum is lighter and less expensive, making it suitable for certain applications like overhead power lines.

Higher temperature-rated insulation (90°C vs 60°C) allows conductors to carry more current safely. Common ratings include THHN/THWN-2 (90°C), XHHW (75°C), and older TW wire (60°C).

Open air installations typically allow the highest ampacity due to better heat dissipation. Buried direct burial and raceway installations may require derating depending on soil conditions and raceway fill.

No, the tabulated ampacity values assume standard conditions (30°C ambient, 3 or fewer conductors). Real-world installations often require applying correction factors for temperature, conductor count, and installation method.

Recalculate ampacity whenever you change wire size, add conductors to a raceway, modify installation methods, or when ambient conditions change significantly from the original design parameters.