I have an EV charger that uses a NEMA 14-50 outlet with 6 AWG back to a 50 amp breaker. The outlet is in a location where there are no nearby 120 V outlets and it would be convenient to occasionally to have 120 V there instead.
Functionally it is possible with just a dryer plug, a 20 amp duplex outlet, and a box to create an adapter to convert (in the functional sense, not physics) the 240 V outlet into 120 V.
Edit for clarification: I'm not talking about making a permanent hard wired change to my home's wiring. I'm talking about a stand alone adapter that I can unplug the EVSE and then plug in this adapter on an as needed basis and then switch it back. In this way it's impossible for both to be used simultaneously.
One safety failure of the adapter is if a device pulls more current than its own cord (or internals) can handle but less than 50 amps because it wouldn't trip the breaker and potentially cause a fire. Is there anything else I'm missing? I saw some inline circuit breakers on Amazon for up to 250 VAC 20 amp. Would that be a way to fix the safety issue or am I thinking about it too simplistically? What is wrong with adding these sort of circuit breakers to the outlet?
Another clarification: I'm not interested in adding a subpanel for a few reasons.
- It requires a permit
- It is more expensive even setting aside the permitting cost
- It's cumbersome on the wall
- It would then allow the car to charge while also using the 120 V at the same time. In doing so, it may trip the 50A breaker since the car pulls quite a bit of current unless. I recognize that I could reduce the charging rate but I don't want to.
Best Answer
You can't just slap up a subpanel anytime you want to split a 240V plug. However, with a NEMA 14, you can -- because it has all the right wires to feed a subpanel.
So, that's it. You convert the 6/3 cable run into a "Feeder" to the subpanel.
As feeder, 6/3 cable is rated for 55A. They don't make breakers that size, so the feed breaker (in your main panel) gets bumped to 60A.
Eaton CH and Square D QO have perfectly compact 8-space panels, and that's the way to go if you are cramped for space. Otherwise if you match your main breaker's type, you can reuse that 50A breaker.
You don't need a main breaker in this panel, unless the building is detached from the house (and then you do). If so, either choose a panel with a main breaker, or those 8-space panels can have a main breaker added via backfeeding.
Install a 50A breaker to feed that EVSE socket. Then install as many 15A or 20A breakers as you please to supply receptacle loads. You can safely use two 120V circuits at the same time while charging. Realistically due to the 80% rule, your EVSE will actually pull 39A and your random power tools will pull 12A per leg. So you're at 51A which is not a challenge for the 6/3 or the 60A feed breaker.
You can't overdo this. If you're really going to town and running the saw, dust collector, compressor for blowing sawdust away, shop vac for your apprentice to pick up sawdust, etc. -- then the EV is certainly not in the garage at this time!