Ambient temperature for solar

Merry Christmas
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mlnk

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The NEC says to allow for a 30 degree F temperature rise for rooftop sunlight. But experiments in Las Vegas confirm a rise of 30 degrees in winter, but a rise of 59 degrees in summer. This is for EMT. PVC, or rigid mounted 5/8 " off the roof. The difference in the de-rating factors is .71 vs. .41
For # 10 wire THHN 40 amps x .71 =28.4 amps
40 amps x .41 = 16.4 amps
This is a big difference. Mounting the conduit 3" above the roof is supposed to help. But my question is what factor should we use?
 
I would base the calculation on worst case scenario.. I have been designing solar here in the mtn's of Colorado and I can tell you the sun gets hot here. I can only imagine the heat on rooftops in Vegas. Better to be safe than sorry... IMO
 
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