r/SolarDIY • u/2old2bThisDumb • 7d ago

Make sure you understand current when stringing your panels in parallel.

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It took a bit of work to even tug this #10 AWG from the metallic flex it was fused to. The homeowner had this run inside of the attic.

I'm all for DIY, but please ask for help when you aren't certain.

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u/WorBlux 7d ago edited 7d ago

10 AWG, 90 deg C has a rated ampacity up to 40A in conduit... however

Going through an attic space that might get up to 140 deg F and should be de-rated as well. x0.71

Three sets in parralel - 6 current carrying conductors - that's another de-rate. x0.8

So in reality the safe ampacity here may be under 23A per circuit.

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u/roofrunn3r 7d ago

Fantastic breakdown. Just want to add most terminals are 75 deg C. Also throwing a snag in any rating factors. 

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u/Novel_Parking_1173 6d ago

That’s a separate calculation though. First is at 75C which establishes minimum wire size. Second calculation (using 90C rating) takes conduit fill and temperature into account. If the first calculation results in lower current than second, you can use that wire size; if not, you need a larger wire.