[RE-wrenches] 310.15(A)(2) Exception

[Drake]

I think this answers a question I was 
pondering.  If a conduit is run on standoffs over 
a roof, the temperature is cooler than on the 
roof, so the derating of the wire's ampacity is 
less.  It would appear from 310.15(A)(2) 
Exception that it would not be necessary to limit 
the ampacity of the wire to that of the hottest 
temperature zone, which is zero distance above 
the roof where the conductors penetrate.

Is this a correct interpretation?

Thanks,

Drake

At 01:51 PM 8/17/2011, you wrote:
>As I read the rule, that 100' in the trench 
>allows you to go 10' above grade on each side 
>while just worrying about the ampacity in the 
>100' section (be sure to check that your 
>terminals are OK). For 200' in the trench, 
>you're still looking at 10' above grade on each 
>side. The rule doesn't say that you can only use 
>this exception once per circuit, so it's fine that you use it once at each end.
>
>
>On 2011/8/17 12:22, Brian Mehalic wrote:
>>Question about the 10'/10% rule - the exception states "adjacent
>>portions of a circuit."  How does this apply to an underground conduit
>>run, where there are two ends exposed to higher ambient temperatures
>>than the length in the ground?
>>
>>For example, what if there is 100 feet in the trench, and 7 feet above
>>grade on either side? Can the exception be applied? How about 200 feet
>>in the trench and 7 feet above grade on either end?
>>
>>Thanks,
>>Brian
>>
>>--
>>========================
>>Brian Mehalic
>>NABCEP Certified Solar PV Installer™ R031508-59
>>IREC ISPQ Certified Affiliated Instructor/PV US-0132
>>PV Curriculum Developer and Instructor
>>Solar Energy International
>>Carbondale, CO 81623
>>http://www.solarenergy.org
>>
>>
>>
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Drake Chamberlin
ATHENS ELECTRIC
OH License 44810
CO license 3773
NABCEP Certified PV
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