How can you wire one half of a 20 amp 120 v duplex wall socket to run 240 volts over 2 legs 2 separate 120 v legs?

Answer 1

You can't. I'm not sure exactly what you're trying to do, but the way it is written is not possible. It seems you might want to use half of a duplex receptacle for 120 and half for 240. This would not be code compliant, nor would it make sense. A plug designed for 240v will not even fit into a 120v receptacle. You need a 240 volt receptacle rated for the amperage you will need. Also, an existing 120v receptacle has nothing to do with your 240v receptacle. For a 240 volt receptacle, you'll need to run 2 new 120v lines (in the same cable). The existing 120v circuit cannot be used here, even if you added another 120v circuit, because when a load uses 240v, both 120v circuits supplying the 240v must be controlled by a common disconnect (a 2 pole breaker designed for 240v circuit). My advice would be to show an electrician what you want done. I'm sure they can tell you how to make that happen.