THHN

[jondoss82]

Everything says (aside from temp changes) use the 75 degrees column. But THHN is is in the 90 degree column. Do you still use 75 per usual or the 90 in code? I can't seem to find a definitive answer

 

[roger]

The lowest number in the chain is what determines what you use. If the breakers, terminals, buss bars, equipment is rated for 60 or 75 deg that is the limit period. For reference see 110.14(C)

Roger

 

[jondoss82]

Thank you!!

 

[winnie]

And if you jump through sufficient hoops that you actually have proper 90C terminations, then yes you can use the 90C ampacity.

This is rarely practical, however. Perhaps once in a blue moon you need to push maximum current through a space constrained situation.

What is far more common is to have parallel conductors where you will have 6 or 9 CCC in a single conduit, and you base your derating on the 90C ampacity.

Jon

 

[farmantenna]

Everything says (aside from temp changes) use the 75 degrees column. But THHN is is in the 90 degree column. Do you still use 75 per usual or the 90 in code? I can't seem to find a definitive answer

ampacity depends on terminal temp rating but start at 90deg column for ambient temp or multiple conductor count in pipe and you'll get derated maximum ampacity close to the 75 deg column.

 

[jondoss82]

Git it. Thank you all.

 

[kwired]

600 volt and below equipment is nearly always 75C terminals.

As mentioned you can use 90C values for ampacity adjustments, but final adjusted conductor still must be no smaller than the required conductor at 75C for the sake of the terminations.