Conduit/conductor # Derating

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Sol4rguy

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Utah
I'm having a bit of a tough time understanding whether or not to count my neutral as a current-carrying conductor. How do I know if the conductor carries the 'unbalanced current from the other conductors of the same circuit' or not (310.15(B)(4)(a))?

As an assignment I'm designing a 3-circuit 240-volt solar system.

Using #10 wire I start out with ampacity of 40 amps

Because the conduit will be installed 1" above the roof I add 22 Celsius to the ambient temp and then derate the capable ampacity by 71%

Here's where I don't know what to do: to derate by 80% for 6 conductors (3 black, 3 red) or by 70% for 9 conductors (3 black, 3 red, 3 neutral).

I appreciate the help. Please excuse the ignorance, trying to learn this stuff on my own and with the help of you guys.
 
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