@james_s - fair enough. I'm curious though if such a thing were possible, why would anyone bother with a step up transformer. Also in something like that how would you account for differences in the circuits breakers. Ie one plug has a 20amp breaker while the other has 15amp breaker.
@Ian.M - You wouldn't happen to know any company who has designed such a device that would be able to do that?
If you don't need high power 240 volts it's much simpler to just do a step up transformer.
Then you don't have to deal with locating 2 outlets on different phases, since most likely that will be in another room so then you have extension cords running around Etc.
But for high-power 240 volts like what you need, a step up transformer becomes expensive, heavy, and most importantly requires way too much power input at 120 volts.
And in that case making an adapter is not a completely terrible idea. But you still need to separate outlets on different circuits.
so most likely you will need a cord running off into another room in addition to the room that you are in.
Ideally you would include some relays in this adapter so that it only connects the output when it gets both inputs. That also make sure that there is never any exposed voltage on the male pins. and if a circuit breaker trips it will protect any other loads on that circuit from possibly seeing voltage.
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