In the 2008 NEC, article 310.15 says you must derate conductors in conduits that are exposed to sunlight on rooftops. Table 310.15(B)(2)(c) shows a temperature adder depending on how far away from the roof the conduit is. For example, if the conduit is 12" from the roof, you must add 25 degrees F to the ambient temperature. My question is, what do you use for the ambient temperature? Would you use the average high temperature for the summer months or the average high for the entire year?
2008 NEC Revision for Article 310.15
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barbeer
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- Pinellas County, FL
You might get the specified ambient temperature from the building codes.
weressl
Esteemed Member
This is one of the biggest sloppiness of the Code. There are different methods of establishing thermal capacity and different studies shown that as long as a base is established a constant can be developed. Example, for transformer loading the thermal capacity is established during the average temperature in an 8 hour period as the maximum temperature. There is no such stipulation in the Code, not one hour, not 3 hours, nada. If you take the Code verbatim then the maximum momentary temperature is the applicable data.ICS said:
Nuts......if you ask me:grin:
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I just had a question based on the 2005 NEC and it was worded: Type RNC installed 3' above a roof deck has an ambient temp of? 25,30,60,90
It states 50 in the RNC section under installations not allowed, but as you can see, it's not a choice. They aren't supposed to be using the 2008 stuff yet, so where in the world is the answer?
so....................
I just had a question based on the 2005 NEC and it was worded: Type RNC installed 3' above a roof deck has an ambient temp of? 25,30,60,90
It states 50 in the RNC section under installations not allowed, but as you can see, it's not a choice. They aren't supposed to be using the 2008 stuff yet, so where in the world is the answer?
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