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I'm in the US.

I will be installing a 240v outdoor outlet for an EVSE (electric car charger). However, in a few years I will have a garage built (elsewhere) and will move the EVSE to the garage, so won't need the 240v outlet anymore. At that point, I will instead use that outlet for my workshop and would like to have two 120v circuits: one for lights and a 120v air conditioner, one for power tools.

[Edit: the workshop will be for power tools and the garage will be for parking/charging the car. They are not the same structure, the garage is unrelated to this question and will be far far away.]

Is this possible with a single 240v cable? Alternatively, would it be possible to start with two 120v circuits of opposite phases, and wire them together to create 240v and then later go back to two 120v?

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Yes, just be sure to run a 4 wire circuit (2 hots, neutral and ground), if the current garage is attached you don't need extra ground rods. In fact, since you are planning for the future, you might install a sub-panel now that would supply your EVSE outlet as well as other circuits in the future. As many others have said here, go bigger than you expect to need on the sub-panel, they are cheap compared to upgrading later. It's OK for the sub-panel to have greater capacity than the feed to it...no problem. Just make sure the breaker is appropriately sized for the wires feeding it.

You can't do this with 2 separate 120v cables, not code allowed.

EDIT: Of course be sure the wires or cable are of sufficient size to feed the EV charger and future needs. (should have included that with my answer). I also got ahead of myself regarding needing ground rods or not because I was already thinking about sub-panel. Clearly you wouldn't need additional ground rods if it was just an EV charging outlet.

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  • Agreed, this is the exact use case for a subpanel. And going that route, OP won't even need to remove the 240 outlet to get 120 as well (which could be handy if a welder is ever needed).
    – Nate S.
    Sep 4, 2020 at 21:42
  • Agreed, by the time you do all the work and mount the boxes, you could install a sub panel...+1
    – JACK
    Sep 4, 2020 at 23:11
  • I may have confused by mentioning the garage--it will be on the other side of the property, totally unrelated to this except that it's the reason I won't need 240v anymore. :D
    – brentonstrine
    Sep 5, 2020 at 2:34
  • You used the terms "garage" and "workshop". Is the new "garage" you are planning really the workshop, or are you turning your existing garage into a workshop? If you want to use the EV charging circuit when no longer needed for a separate building, you can do that, but the connections will need to be permanently accessible and you'll need a couple of ground rods at the new building. And remember that neutral and ground must be separated (isolated) in sub-panels.
    – George Anderson
    Sep 5, 2020 at 13:48
  • Garage and workshop are different buildings on opposite sides of the yard. The workshop is adjacent to where the outdoor outlet (for car charging) will be. So you're saying that when I re-wire it to be two 120v circuits and point the outlet the opposite direction (in to the workshop) I will additionally have to install grounding rods, because it's a separate building?
    – brentonstrine
    Sep 6, 2020 at 22:39

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