Electrical Code Question

My garage has a single 15A circuit that's shared with the kitchen lights. I want two circuits so that I can run a power tool at the same time as the shop vac, and I want 240V so I can charge my car faster. Ideally I'd run something like a 50A circuit to a sub panel, but installing the sub panel is a fair bit of work and cost to do it correctly. For example since it is a detached garage my understanding is it requires grounding rods pounded into the ground for a sub panel.

I had an idea to limit the scope of the project. If I run a single 10/3 wire (oversized from 12/3 minimum) out there on a 20A two pole breaker, I could install two 20A circuits (multi wire branch circuit style) and also a 240V NEMA 6-20R or 14-20R for charging the car. Is there anything in code that prohibits this arrangement? It's a little unusual, but I think it should be safe as long a I use a GFCI protected breaker. I would just have to not use power tools at the same time as charging the car, but that's no different than now. The 2017 NEC is in use in my area.

 

Thanks for the detailed replies.

Technically it sounds like if I need to meet 210.11(C)(4) and 625.40, then I need three circuits because I need another one for the light.

How does the code know if my outlet is installed for the purpose of EV charging? Could it just be a generic 240V receptacle that I happen to plug an EVSE into? I'm planning on using a portable EVSE not a permanently installed one.

To meet 210.11(C)(4) (ignoring 625.40) and also have 240V available, could I make an adapter cable that plugs into two 15-20R receptacles on opposite hot legs, and converts that to a 240V receptacle? For example something like this. Making my own adapter sounds more dangerous than just putting in a 240V receptacle, and taking it out if I ever move.

 

Thanks! I am an electrical engineer, but I work on electronics not building wiring.

I'm aware of the requirement for grounding. I'm not planning on leaving the existing 15A circuit. It also serves the kitchen lights and range hood. I think the range hood precludes much else from being on the circuit, but I can't remember which requirements apply.

I'm confident that I could run a MWBC and add receptacles in the garage. But a subpanel adds just enough complexity that I should probably hire an electrician. That significantly increases the cost. I'm not sure how long I plan to live in this house, so I don't want to invest a lot in garage wiring. Maybe having an EV charging outlet in the garage would be a selling point, but it's probably not a significant consideration.

For load calculations it looks like I can use 220.83 "Existing Dwelling Unit" which is much more generous than the rest of 220 III. I'll have to do more research. I only have 125A service, and I'm strongly considering replacing the electric water heater with gas to free up capacity, free up space in the main panel, and to save money on water heating. I would also like to add another mini split air conditioner in the future if I stay in this house.

Regarding whether 210.11(C)(4) applies, I am never sure how much the latest code applies to new work in existing buildings. I am assuming that since I plan to redo most of the wiring in the garage, that it would fall under the current code. But this requirement does seem like it's intended to be a standard for new buildings.

The only local amendment that appears to be relevant is that AFCI requirements apply to new panels and subpanels. Luckily that doesn't require my main panel to be upgraded to AFCI, since that would be a lot more expensive. I don't mind putting AFCI breakers in a new subpanel (I'm a fan of safety devices).