Temp. adjustments

[ceb58]

I am putting together a price for sign lighting and I want to double check my derating. My conduit will run on top of a metal roof. By 310.15 B 2 C I am going to be between 1/2" and 31/2" so my adder is 40 deg F. For my area I am using the 96-104 amb. temp from 310.16. So by that I would need to figure for 144 deg.F at the worst. The adjustment is 0.58 for wire in the 90deg. coll. I need a 20amp circ. for the signs so by this #10 would work out at 23.2 amps. Would this be correct or do I have to calculate from the 75deg. coll.? This would put me running #6 for the circ.

 

[cadpoint]

I'll probably get this wrong! You where right up to 144? (if thats the number) you take the percentage as listed as a multiplier from the table at your temp. of 144? and mutliply againest the desired working size, then work voltage drop due to distance if required!

 

[nakulak]

110.14 C says that you can use the higher rating (ie 90) for ampacity adjustment and temperature correction

 

[ceb58]

110.14 C says that you can use the higher rating (ie 90) for ampacity adjustment and temperature correction

Thanks, I just wanted to double check my self.