When determining wire size for a given amperage is it permissable to use the 90 degree rating or should it be sized to the 75degree? Seems that I either was told or read somewhere that most if not all terminations(lugs etc.) are only rated at 75 degrees anyway. I know the 90degree is used for derating purposes but am not sure on the ampacity aspect of it. Am I missing someplace in the code that tells me this? Thanks.
Conductor ampacity
- Thread starter nizak
- Start date
- Status
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
You may use the 90C ampacity for derating but unless all the terminals, etc are rated 90C you will have to size the wire to the weakest link. Thus with NM cable we know that it has 90C wire in it and we know that most of todays terminals are rated 75C but NM is rated 60C based on 334.80. In this case we must use the 60 C rating. In most other cases where MC or conduit is used we can usually use the 75C ampacity.
Rewire
Senior Member
- Location
- Lake of the Ozarks
I see this on test questions they give all the info on load and ambient temp conduit fill then sneak that 60c lugs in at the last.
- Status