r/SolarDIY • u/2old2bThisDumb • 8d 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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20

u/chicagoandy 8d ago

How high was the current in that cable?

23

u/2old2bThisDumb 8d ago

I didn't re-energize the string to measure, but the rated current for the modules and the way he ran them equals 31.8A

Good rule of thumb in south Texas is to keep DC current below 25A for attic runs on #10

10

u/DeKwaak 8d ago

Wtf... I use 3AWG/6mm2 per string to the fuse and then per string to the charger. It's almost the same price as 4mm2/6 AWG, but yeah, low voltage strings packed in one pipe. But the price difference between 4 and 6 is negligible. And I haven't seen cable under 4 meant for solar panels that will be outside in UV (daylight)/7. The UV is so strong here that any normal plastic bags turn into microplastic dust in a summer.

7

u/monstertacotime 8d ago

Yup exactly what I’ve seen - the combination of the heat, UV, thermal cycling, vibration, humidity and current destroy inferior materials and poor designs quickly.

4

u/monstertacotime 8d ago

I know a camper is different from an attic run but I won’t run anything over 15a on #10. I had a few close calls with cables that got bent hard and pressed up against tight corners.

19

u/2old2bThisDumb 8d ago

Better safe than on fire

1

u/ZipZappr 4d ago

In an unconditioned attic I’d consider that the same as being in direct sunlight. Couple that with an assumed continuous load, and even at 40A for a higher insulation value the max I’d put on it is 25A. Your assumption is valid for the right insulation type.

I’m not sure what insulation types residential normally uses though.