Converting 220V to 110V without neutral conductor

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Rick Barndt

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Here's the situation: a detached garage with only a 12g 110V supply line running under a lot of concrete (big $$ to change service). The owner got an EV and would like to have 220V/20A to plug the car in for faster charging. The wiring in the garage is old and not up to current code (no GFCI for example). Here is my proposed solution:

1) Install a new double pole 20A breaker in panel at house and move this circuit to that breaker, thus providing 220V without neutral to garage. Label the white wire as "hot".
2) In order to provide 110V power in garage, install a properly sized 220->110 isolation transformer in the garage in parallel with the 220V outlet for the EV only.
3 Since the 110V output is floating that is not ideal since neither side is neutral. I propose to ground one side of the output and then use a GFCI breaker after this point.

I believe this is safe and would not allow current to flow through ground without tripping the GFCI. It is probably safer than the existing conditions. I cannot find any relevant threads on this topic. Any pointers or comments?
 
Seems to be a violation of 625.40:

c53e08c96888e2f9188986e98914532b.jpg
 
Welcome to the forum.

You're still going to be limited to (20 x 240) 4800 kva total.

I would suggest a new feeder to a new panel in the garage.

Can you engineer an adequate overhead run instead?
 
retirede said:
Seems to be a violation of 625.40:

c53e08c96888e2f9188986e98914532b.jpg
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That's not really the problem, he can install a panel and feed EV circuit and transformer as separate branch circuits.

Overall ampacity if the branch circuit is still kind of a big problem. Like, the EV circuit would probably need to be only 15A so that any other load doesn't trip the feeder breaker. I agree with others that this barely seems worth it and the customer should really consider the cost of a new higher amp feeder.
 
jaggedben said:
That's not really the problem, he can install a panel and feed EV circuit and transformer as separate branch circuits.

Overall ampacity if the branch circuit is still kind of a big problem. Like, the EV circuit would probably need to be only 15A so that any other load doesn't trip the feeder breaker. I agree with others that this barely seems worth it and the customer should really consider the cost of a new higher amp feeder.
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Or selling the EV and getting a hybrid.
 
Thanks all. A couple of things: First, the current to the car would be limited to 12A because the customer is using the charge cord supplied with the car. Going to 220 doubles the charge rate from about 4mi (of range) / hour to 8 mi/hr. Quite a difference. A level 2 charging station would be required for higher current. Second, the ampacity is not an issue as normal load for the 110V is just lighting. It is understood that the car cannot be charged while running an appliance like a vacuum cleaner, etc.

Yes, it is a hack job for sure, but safety is the primary concern.
 
Rick Barndt said:
Yes, it is a hack job for sure, but safety is the primary concern.
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I think that we all agree on the hack part. ;)
Having said that it might work but you then need a GES and a GEC from the transformer. As zbang mentioned a white conductor in a raceway cannot be re-identified as an ungrounded conductor.
 
What is the plug on the line side of the charger supplied with the car? If you are intending to wire a NEMA 5-15 or 5-20 receptacle for 240V, you can add that to the list of reasons that what is being proposed is a terrible idea.
 
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