Conductor Correction Factors

[Strahan]

Ok I need just alittle clarification on this topic. When correcting the ampacity of conductors either for ambient temp or more than 3 current carrying conductors bundled in raceway why do we use the 90C column for correction factors?
When sizing conductors this column cannot be used circuits rated 100A and less use the 60C column and circuits 100A and more use the 75C column (unless terminals are marked otherwise). So why do we use the 90C column for correction factors? And do we apply this correction factor to the correct size wire determined from the 60C and 75C column? Thanks

 

[chris kennedy]

90?C should be used.

110.14(C) Temperature Limitations. The temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected termination, conductor, or device. Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both.

 

[Strahan]

90?C should be used.

Missed that in the code. So this permits the use of conductors in the 90C column to be used eventhough code says to size conductors according to the other columns depending on circuit amperage? Lets say I size a conductor #8 40amps per 60C column and I have an ambient temp of 90F correction factor would be .96 after the math I come up with 38.4 amps that this conductor is cable of in this situation. I need it to be capable of 40 so do I go to a #6 or do I go to a different insulation type such as THHN in the 90C column?

 

[Strahan]

90?C should be used.

Disregard my last post I got it now. Going through Mike's prep book here refreshing my brain because it's been awhile and confusing myself thanks Chris