first one is a 120V single pole... not double pole
Whoops!
That brings up an interesting point. I mentioned earlier that I had never seen a double-wide breaker that was not dual-pole. And now I have.
So... it is possible that the 20A breaker in the main that feeds out to the garage is only a single pole breaker.
CidahMastah.... is the cable that is buried under the ground a 4 wire cable? That's critical here.
So you are saying that, with the 10gauge line I have I could get a dual pole 30amp breaker for the main panel.
I would check with an electrician to make sure that the ampacity rating of the 10AWG wire, when buried under the ground, is still 30A first. There are several things that factor into the max amp load of a wire.
- metal type
- wire gauge
- insulation used on the wire
- wire length
- "form" (single wire, multi conductor cable, in open air vs inside of conduit)
SO, don't just assume that 10AWG wire can handle 30A in all situations. I'd love to offer you a specific answer, but I am an electrical engineer and not an electrician, and these kinds of things are not taught in school for an engineer. An electrician will be able to answer with more authority on those kinds of things.
From that, keep the 10g wire in and replace only the subpanel with a 100Amp subpanel. In that subpanel I would keep my current circuits (20, 15, 15) breaker set up and add a 30 amp GFI breaker, so that 30 amp breaker on the main panel would be split into 4 circuits (20,15,15,30)? On the 30 amp GFI breaker I would wire up a 240 outlet?
That's one option. The other would be to put the GFCI breaker in the main pabel instead of the subpanel. That would protect everything in the garage at the same time.
As I mentioned, GFCI breakers can get expensive and you'll have to shop around for a deal. So, it might be in your wallet's best interest to get your subpanel first and then decide (based on what kind of deal you can find on the GFCI breaker) whether you want to put the GFCI in the main panel or in the subpanel.