I would like to design a circuit which would have TWO normal USA (NEMA 5-15P) plugs, and when plugged in to two outlets, would detect not only if these are wired corrctly (e.g. like an ordinary circuit tester), but also detect if there is 240 volts between them.
THE BIG SAFETY ISSUE: there must be NO VOLTAGE on the 2nd plug's prongs when the 1st is plugged in, regardless of which is plugged in first.
I have not yet started to design this. I've just recognized a need to have such a device, but have never seen such a device.
Additionally, I'd like it to be able to detect 240 volts between outlets even if either or both are wired wrong.
And then later, I'd like to add on a capability to detect if this circuit is wired with a shared neutral, or wire with separate neutrals back to its panel source. In this case it would require an ohmmeter sensitive to the subtle difference in low resistance of the lengths of wire that could be involved.
Any suggestions (other than from the knee jerk reactionists that always tell people to forget it).