Sweating question

PaulEd

Member
Location
United States
Having a brain (blank) here guys

According to the national electrical if I need to derate conductors and for example, I have XHHW which is rated from 90°C, but I install it on a roof where XHHW is only rated at 75°C. (Outdoors) can I still derate from the 90° column or do I need to debate from the 75° column?
 
You would have to use the highest rating of the conductor and if that is 75 deg for the application that's where you would start.
 
Paul, I'm not sure I was right. 110.14(B)(1) says to use 310.15(B)(16) regardless, so you could use 90 deg
 
Paul, I'm not sure I was right. 110.14(B)(1) says to use 310.15(B)(16) regardless, so you could use 90 deg
You were right the first time. In (2017 NEC) Table 310.15(B)(16), XHHW is listed over both the 75C column and the 90C column, because it is 75C wet, 90C dry. So if used in a wet location, you would use the 75C column.

Cheers, Wayne
 
Having a brain (blank) here guys

According to the national electrical if I need to derate conductors and for example, I have XHHW which is rated from 90°C, but I install it on a roof where XHHW is only rated at 75°C. (Outdoors) can I still derate from the 90° column or do I need to debate from the 75° column?
When derating u are allowed to use 90 degree column. u only use the the 90 degree column when you are derating, other than that u use 75 or 60 degree depending on lug ratings
 
You were right the first time. In (2017 NEC) Table 310.15(B)(16), XHHW is listed over both the 75C column and the 90C column, because it is 75C wet, 90C dry. So if used in a wet location, you would use the 75C column.

Cheers, Wayne
When derating u are allowed to use 90 degree column. u only use the the 90 degree column when you are derating, other than that u use 75 or 60 degree depending on lug ratings

Lordofthisworld (I can't believe I just had to write that out LOL) I would think Wayne's comment is more accurate no? If a wire is only rated for 75deg (in my example it was XHHW but use any other wire) in say a wet location why would I be able to use the 90deg column?
 
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