Full house panel/detached garage sub

[TheBreu]

Hello all, I have 100 amp service in the house, panel is full, garage detached with a 240 plug. Wire into the panel shows 10/3 on a 30 breaker for said plug in the garage. I assume there is a separate ground run out there (haven't pulled J box cover to look, too cold out).

Wire travel to get to the garage is less than 30 ft. I want to put in a sub panel in the garage to add more 120 plugs and circuits for lights etc. I also want to change the 240 plug to a generator connection. I planned on running new #8 wire from house to garage so I know exactly what I have. I am aware of needing ground rods at the garage for the new panel. My question revolves mostly around the full box in the basement. Do I need to run 2 separate sets of #8 to power the sub and the generator to be legal with the interlock? My thought is because if it's all on one circuit, when you are not running the generator, the breaker to feed the sub to the garage will be locked out. I can free up a couple circuits in the main panel since they also run to the garage for the existing plugs and lights.

I hope I phrased the question right

 

[wyliesdiesels]

Shouldnt be a separate ground wire as 10/3 NM-B has a ground wire. The ground wire in NM wiring isnt counted.

And if i understand u correctly, u want to power the garage AND the house with generator. If thats the case then the breaker for the generator needs to be in the main panel with either a transfer switch between the incoming utility lines and the panel or an interlock between generator and main service breaker. Why not just put an outlet near your main panel and save the hassel of running 2 sets of wire...