Which temperature rating does the ampacity in NEC comply with?

The ampacity ratings provided in the National Electrical Code (NEC) correspond specifically to conductors and their performance at different temperature ratings. In the NEC, the standard temperature ratings for determining the ampacity of conductors are primarily based on the 75 degree Celsius and 90 degree Celsius ratings. These temperature ratings are critical because the ampacity of conductors can vary significantly with temperature; therefore, the NEC specifies these ratings to ensure safety and reliability in electrical installations.

At 75 degrees Celsius, the ampacity reflects a standard operating environment for many insulated conductors, which is commonly applied in residential and commercial electrical wiring. The 90 degrees Celsius rating represents higher-temperature-rated conductors, which may be used in specific applications where increased temperature tolerance is needed.

In contrast, the other options either specify temperature ratings that are not used for ampacity calculation, such as only at 60 degrees Celsius or restrict the focus to temperatures that are not relevant for commonly used conductors. Thus, the correct answer reflects the established standards within the NEC for determining safe and effective conductor usage.