#10 AWG wire ampacity

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hhsting

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I have #10 AWG Thwn-2 for solar panel job from inverter to junction box in conduit. I am wondering should the ampacity of #10 AWG Thwn-2 be 30A per NEC 2014 Section 240.4(D) or 35A?
 
electrofelon said:
yes for derating. In fact you can use 40 for derating, the 90 degree rating of #10.
Click to expand...

Right but 75C is for equipment rating. Ok so let’s say I have #10 AWG thwn-2 total 8 conductors with 80% derate in one conduit +,_ DC going to solar panel optimizer strings/modules. The ambient temp is 35 C and rooftop add is 22 C so total is 56C based on table 310.15(B)(2)(a) is 71%.

My optimizer max output current is 15A.

So I can use 35x0.71x0.5= 19.88A so 10AWG should be ok?
 
10 awg (assuming it is THWN) is rated for 40 amps in the 90* column. So you would do all of your adjustments off of the 90* column. After you do your adjustments, what ever number is lower between your adjustment number and the 75* column would be what your wire is rated for.
 
So 40amps x 0.7 (8 conductors with 70% adjustment factor) x .77(adjustment for 56*c temperature adder) = 21.56 amps.

So the 75* columns says you are good for 35 amps and the number after doing adjustments on the 90* column (for 90* wire) comes out to 21.56 amps. So you have to go with the lower number. Your wire is good for 21.56amps.


FYI, adjustment for 7-9 conductors is 70% not 80%
 
SSDriver said:
So 40amps x 0.7 (8 conductors with 70% adjustment factor) x .77(adjustment for 56*c temperature adder) = 21.56 amps.

So the 75* columns says you are good for 35 amps and the number after doing adjustments on the 90* column (for 90* wire) comes out to 21.56 amps. So you have to go with the lower number. Your wire is good for 21.56amps.


FYI, adjustment for 7-9 conductors is 70% not 80%
Click to expand...

So 75 C column would be lower no? Also don’t I have to multiple optimizer output current by 1.25 and then compare?
 
75c column would be the wires MAXIMUM allowable usable ampacity for equipment termination points. 310.15(B) allows you to use the wires insulation rating for adjustment factor calculations. So 75*C column would be taken at face value(no adjustments made off of this number) and the 90*C column would be used for calculations. What ever number you get after doing your calculation off of the 90*c column can not exceed the ampacity of the equipment termination rating (or 75*c column for almost everything). I don't work with solar so I'm not sure about the optimizer current requirements in regards to wire size. But for calculating the wire ampacity this is how you would do it.

310.15 (B) said:
B) Tables. Ampacities for conductors rated 0 to 2000 volts shall
be as specified in the Allowable Ampacity Table 310.15(B)(16)
through Table 310.15(B)(19), and Ampacity Table 310.15(B)(20)
and Table 310.15(B)(21) as modified by 310.15(B)(1) through
(B)(7).
The temperature correction and adjustment factors shall be
permitted to be applied to the ampacity for the temperature rating
of the conductor, if the corrected and adjusted ampacity does not
exceed the ampacity for the temperature rating of the termination
in accordance with the provisions of 110.14(C).
Click to expand...
 
SSDriver said:
75c column would be the wires MAXIMUM allowable usable ampacity for equipment termination points. 310.15(B) allows you to use the wires insulation rating for adjustment factor calculations. So 75*C column would be taken at face value(no adjustments made off of this number) and the 90*C column would be used for calculations. What ever number you get after doing your calculation off of the 90*c column can not exceed the ampacity of the equipment termination rating (or 75*c column for almost everything). I don't work with solar so I'm not sure about the optimizer current requirements in regards to wire size. But for calculating the wire ampacity this is how you would do it.
Click to expand...

Ok thanks. Anyone here work with solar know?


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