Wire Insulation

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bcorbin

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I have been accustomed to specifying THHW for a while. However, I am getting feedback from contractors that say it is basically non-existant anymore. Looking at dual-rated cable, say THWN-2, all of the manufacturers I have seen only produce it in #8 or larger.

So what is being used out there when you need 90 degrees, wet location, in a #10 or #12?
 
Many conductors will be marked as two or more types indicating that they meet the listing requirments for each type.
With # 12 & # 10 we use thhn/thwn it has a dual rating.
 
Right....but thhn/thwn is only good for 75 deg. C wet. Am I just out of luck for a 90 deg. C cable in those sizes?
 
Thanks, fc. Looks like it might be time to update that spec or add another manufacturer to it. :smile:
 
I don't know of any terminations for small conductors that are rated 90 degree C so you will probably be using the 60 or 75 degree rating for the wire anyway.
 
I don't know of any terminations for small conductors that are rated 90 degree C so you will probably be using the 60 or 75 degree rating for the wire anyway.
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But the 90?C rating is often used for derating purposes.
Don
 
Well, this problem was resolved today, but not in the way I thought it would be.

When I called up a major cable supplier rep to see what he had to replace THHW #12, he suggested XHHW, which is more expensive. So I checked the NEC (gasp!) and figured out what had caused this situation...I should have been using the NEC definition of THHW rather than an old manufacturer cutsheet, which listed THHW as 90 dry / 90 wet. The NEC says 90 dry / 75 wet. Wow....sounds like everyday THHN/THWN to me. You would think the rep might have told me this.

I guess Tuesdays are for feeling foolish. :-?
 
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