Ampacity Calculator
Adjusted conductor ampacity with NEC ambient-temperature correction and conductor-bundling derating.
Base (90°C)
55A
Temp factor
×1
Bundling factor
×1
Adjusted ampacity
55.0A
This is the conductor’s adjusted ampacity. The final usable value is still capped by the terminal temperature rating (NEC 110.14(C)) and the 240.4(D) limits on 14/12/10 AWG.
Calculations are built on the 2023 National Electrical Code (NEC) and cross-checked against the published code tables. How we verify. Last reviewed June 2026.
How ampacity derating works
The NEC Table 310.16 ampacity assumes a 30°C (86°F) ambient and no more than three current-carrying conductors. Outside those conditions you must derate:
- Ambient temperature — multiply by the correction factor from NEC 310.15(B)(1). Hotter ambient = lower ampacity.
- Bundling — when more than three current-carrying conductors share a raceway or cable, multiply by the 310.15(C)(1) adjustment factor.
- Terminations — the final usable ampacity is still capped by the lowest-rated terminal (NEC 110.14(C)), usually 60°C or 75°C.
You can start from the 90°C column for the math (most THHN/XHHW is 90°C), but the protected value cannot exceed the 75°C (or 60°C) termination rating.