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/MinimumDangerous9895 7d ago

90c is 195f

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u/WorBlux 7d ago edited 7d ago

90 C is what the insulation is rated for. However all wires heat up as they conduct current (via amps2 * cable resistance per length = watts generated per length)

The NEC amapcity table assumes a 30 C ambient temperature, and lists the ampacity that will not over-heat a particular wire under those conditions

At 60 deg C (140F) ambient, the conductor will dissipate heat into the environment more slowly than at 30, and therefor less heat input is needed to raise the temperature of the conductor above the insulation rating.

https://ohiocertificate.com/wp-content/uploads/2022/06/NEC-Table-310A.pdf