#6 NMB used with solar circuit

JoeNorm

Senior Member
Location
WA
Hello All,

Installing 36 Sunpower AC modules. Each Module is rated at 1.33 Amps AC, 36 x 1.33 x 1.25= 59.85 Amps AC.

We will be combining the module outputs into a combiner panel, which will itself have one output to feed the meter and main panel.

Seeing as #6/3 NM is only rated to 55 amps, am I right coming to the conclusion that it cannot be used here, even though i am pretty certain that wire will never see 55 amps on it, due to losses and the fact that we oversize it for continuous use?

Any thoughts on this?

thanks
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Hello All,

Installing 36 Sunpower AC modules. Each Module is rated at 1.33 Amps AC, 36 x 1.33 x 1.25= 59.85 Amps AC.

We will be combining the module outputs into a combiner panel, which will itself have one output to feed the meter and main panel.

Seeing as #6/3 NM is only rated to 55 amps, am I right coming to the conclusion that it cannot be used here, even though i am pretty certain that wire will never see 55 amps on it, due to losses and the fact that we oversize it for continuous use?

Any thoughts on this?

thanks
The amount of current you expect to see is irrelevant to the code; your design current is (36)(1.33A) = 47.9A. Your temp and conduit fill (if applicable) derated ampacity must be greater than that and (1.25)(47.9A) = 59.9A must be less than the 75 degree wire ampacity, assuming that you have 75 degree terminals. I don't know anything about the ampacity of #6/3 NM cable, though; what is the temperature rating?
 

jumper

Senior Member
The amount of current you expect to see is irrelevant to the code; your design current is (36)(1.33A) = 47.9A. Your temp and conduit fill (if applicable) derated ampacity must be greater than that and (1.25)(47.9A) = 59.9A must be less than the 75 degree wire ampacity, assuming that you have 75 degree terminals. I don't know anything about the ampacity of #6/3 NM cable, though; what is the temperature rating?
Temperature rating for NM-B is 90C for corrections/derating/adjustments but limited to a final ampacity of 60C per 334.80.
 
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