8ga wire large enough?

When getting ready to do my solar install I planned to install 480w with three panels and wanted to have the ability to add another if needed. I went with a 4-2 duplex from the combiner box to controller. The cost difference isn’t much and the larger gauge helps reduce the voltage drop.

The 8 gauge will probably be fine but when I installed 3 panels for 540W I used 6 gauge. About 14 feet from roof combiner box to the controller. Then about 6 feet from controller to the batteries. Used 4/0 for the shunt to the batteries, about 5 feet. System works great but of course never really get the full output from the panels as only one is set up to tilt. But your 450W of solar with your wires should do OK even in the winter depending on number and type of batteries.

I’d say 6 would be better over a 10 foot run. WindyNation tends to agree. https://www.windynation.com/jzv/inf/choosing-right-wire-size

You can go about as big as you like with #8 wire. As you approach 30 amps you can start looking at going series mated to an MPPT controller. My 675 watts only puts out 7 amps to the controller (90 volts).

I'll take exception to using the 40A wire rating. For 120V a 3% loss is small while 3% in a 12V system is much more significant for the battery voltage. It's all about acceptable voltage loss.

Use a wire calculator and decide for yourself. Using 8ga, 14.8V, 10' (ONE WAY) and 30A will give you about 0.4V drop and I'd want less. However the 2.6% loss is not excessive. 6ga would be about half.

14.8V above is the typical bulk charging voltage for flooded batteries. 30A is the gorilla in the room as it depends upon flat vs tilted panels, summer vs winter, latitude, TOD and weather. But I typically use flat, noonish, clear day in the summer.

Check the Samlex site on line, they have a chart of recommended ga to length somewhere there. And lots of other info on wiring up solar and inverters.

donn0128 wrote:
8ga wire is rated for 40A.
450 watts solar array is capable of 37A. So theoretically you would have sufficient cable. Of course 450A solar array is not likely to ever produce the full 37 amps. Unless you have a solar tracking package.

That is excellent info............and exactly the info I was hoping for, making it even more excellent!

Thanks

8ga wire is rated for 40A.
450 watts solar array is capable of 37A. So theoretically you would have sufficient cable. Of course 450A solar array is not likely to ever produce the full 37 amps. Unless you have a solar tracking package.