I have a Eaton 200 amp main panel coming off the meter base. The main panel, at this point, feeds a 30 amp RV outlet and a 20 amp GFCI, and a 90 amp sub panel for the well (30 amp) and a 20 amp GFCI outlet. Can I feed a 200 amp sub panel for my future house/garage that is 150 feet away from the main panel?
Yes, that's fine.
- If you want to carry the full 200A over there, and it's going to a residence, you can use 4/0 aluminum cable with 4 wires (separate neutral and ground). Otherwise run 250 kcmil (the next size up from 4/0).
- If you want to carry less power over there, but you're simply using a 200A panel because it has plenty of breaker spaces, then you can use any wire size you please but you need to have an appropriate size breaker feeding that wire. (e.g. 1/0 aluminum and a 125A breaker).
You didn't mention if you had a ranch panel - that's a panel with a 200A main breaker, a few breaker spaces (4 or 8) and "thru lugs" to allow carrying the full 200A wherever you please. In that case you can tap the 4/0 wires right off the thru lugs.