necnotevenclose
Senior Member
The NEC talks about ambient temperature and derating, but where does the NEC clarify how I determine the ambient temperature?
How Can I Determine Ambient Temperature?
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Hameedulla-Ekhlas
Senior Member
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I dont have NEC book to tell you clearly but if I am not wrong NEC cable is abased on 30 degree and abient temperatur factor for 30 degree is 1. For derating there is clear table factor. It applies in the number of cable increases more than 3.
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- Chapel Hill, NC
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- Retired Electrical Contractor
Good luck. Apparently there is a chart that supposedly gives an ambient temp. for different areas of the country. I have no idea where it is or if it is even pertinent to the NEC.
What is ambient temp. The nec does not define it. The ambient temp during the summer is much different than in the winter. Do we use the average or the hottest month? If we have one day out the year that the temps reach 140 in an attic do we use that? You will not find the answers to those questions.
For the most part the ambient temp is not looked at for residential work but may be enforced in commercial areas where the know temp. of certain rooms is very high.
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- Lockport, IL
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- Retired Electrical Engineer
True, but not relevant to the question. He wants to know what temperature to use, such as whether he can use 30C, or whether he needs to use 35C or some other number, based on the location of the project.
I agree with Dennis, that the NEC does not tell us how to select a temperature. My opinion is that we should use the year-round average. But that has been debated here a time or two, and my opinion is not shared by many members.
That is not true. Derating a cable because it is installed in a hot area is a completely different thing than derating a cable because there are too many other conductors in the same conduit. A given installation might require one derating factor or the other, or it might require both, but they are handled separately.
kingpb
Senior Member
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- SE USA as far as you can go
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- Engineer, Registered
ASHRAE is the document to find temeprature data.
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- Chapel Hill, NC
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- Retired Electrical Contractor
Thank you, I believe that is correct. I think Bryan posted it at one time.
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bphgravity
Senior Member
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- Florida
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- Chapel Hill, NC
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- Retired Electrical Contractor
Thanks Bryan-- I thought it was you that posted it. Good to know my brain isn't totally fried.
antenna2001
Member
You found the answer. I am just posting this in case you have not seen the footprint note on table 310.15(b)(2)(c) where ASHRAE is referred to.
Volta
Senior Member
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- Columbus, Ohio
Thanks for posting that link. I asked our local building department a couple years ago, and they said 90 deg F, which seemed low to me, and I usually go with 100, nice to see it noted roughly both ways.
necnotevenclose
Senior Member
DAMN you guys are good! I want to buy you guys a round!
So if the list does not include your city do you think the inspector will be fine with 75-deg c...:roll:
So if the list does not include your city do you think the inspector will be fine with 75-deg c...:roll:
Hameedulla-Ekhlas
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Charli: thanks for explaination and it is really another new issue for me because I was not aware or faced such a situation.
I just use common sense. If I'm installing something on a black roof top I figure it's going to get hot in the summer so take a guess and derate accordingly. If you're in AZ and you'r putting stuff on a black roof top it's gonna get damn hot so better add in a little more for temp.
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- Massachusetts
That is now required, see 310.15(B)(2)(c)
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