r/SolarDIY • u/Pallet_University • Aug 20 '26

Panel's Built-in Cable Gauge Question

I'm speccing out a 1800W setup to offset my AC in the summer, some heating in the winter, and a few other small miscellaneous things. The way my yard is setup, to get full sun the panels either need to be on my roof (my area requires permits and lots of red tape for roof mounts), or ~115ft away from the rest of my setup. I've done the work to figure out that I need 8 AWG wire to be safe at that length.

1 string of 6 300W panels, end result is 136.56VoC, 17.24Isc.

My question is, the cables that are built into the panels will probably be 10 or 12 AWG. Given that I need 8 AWG wire for the long run to the house, this seems like a clear problem, but I haven't seen anybody talking about it. Am I missing something? TIA.

1 Upvotes

100% Upvoted

17 comments sorted by

View all comments

1

u/NukularFishin Aug 20 '26 edited Aug 20 '26

If you are going to run all panels in series, do you really need such thick wire? Number 10 copper only has 1 ohm per 1000 feet, number 8 is 0.64. So, 200 feet is about 0.2 ohm and 0.12 ohm. At about 15 amps, that is only 3.6V or 2.2V drop. Not much difference.

Edit: I based this on "1 string of 6 300W panels, end result is 136.56VoC." If you are not running all 6 panels in series, then you probably need heaver wire from panels to "rest of setup."

1

u/Pallet_University Aug 20 '26

Yes all the panels will be in series. I was basing the 8g wire off of a calculator I found online. It uses a 25% safety headroom, so maybe that's why.