I only plan on requiring a 35-40 amps (per my load calc) to be fed from the sub-panel initially but would prefer to put in at least a 60 amp panel (breaker).

The feeder to the sub panel would run up a studded/sheetrocked wall, into my garage attic and across to the opposite wall, down this opposite wall and through studs/floor joists and into the basement.

As I see it, my four options are.

1. Run NM 6/3 from main service panel to sub-panel. I understand the NM is only rated for 55 amps but in my research I can round up to 60 and protect this with a 60 amp breaker in the main service panel if my intended load will be no more than 55 Amps. This is definitely the easiest solution but it limits any future expansion to 55 Amps. If I later add a kitchenette in the basement I would be in the 55-59 Amp range when accommodating for the additional circuits (range, small appliances, etc.).

2. Run #6 THHN (6-6-6–8) in 3/4″ EMT conduit from the main service panel to the sub-panel. This is my preferred method since it gives me a true 60 Amps. 75 really… which could possibly be later rounded up to 80; if more than 60 (but less than 75) is needed. My concern with this is I believe I have to run the conduit from service panel to service panel. The gotcha with this is that my interior garage wall sits directly over my basement poured concrete wall. So I would need to bend/offset the 3/4″ EMT inside a bored hole in order to run it down through the wall to the basement and to the sub-panel. I’ve never bent EMT so I’m not sure how difficult this is going to be.

3. Run #4 THHN (4-4-4-8) in 1″ EMT. This would definitely allow for any future expansion but unless my inter-wall offset will be relatively easy with 1″ EMT, this would likely be a complete PITA.

4. 1. Run (2) NM 6/3 cables from main service panel to (2) sub-panels protected by 40 breakers in the main. May be the easiest route to get 60-80 Amps in the basement?

Any feedback, suggestions or alternative solutions?

Edit: I’ve attached a very crude picture of the situation.