Originally Posted by slakwhere
120v uses 1 hot, 1 neutral and 1 ground (which you are STILL ignoring).
240v uses 2 hot, 1 neutral and 1 ground. the 2 hot lines are basically alternating phase 120v. take either hot leg, a neutral and a ground and you get 120v. take 2 hot, a neutral and you get 240v.
this diagram will not work for 240v. you do not understand how 240v works. you're missing 2 inputs to the plug, there's no ground. i have no idea why that 50a shunt is there. there's no heating element in the diagram, so this is a really elaborate switch that turns on a light bulb.
please, for the love of pete, find a buddy who has an electronics background to help you locally. you're missing a LOT of stuff. you're going to burn your house down, electrocute yourself or blow up a lot of gear. most probably all 3.
Actually, 240v does not have a neutral, as 2 hots will do, with a ground for safety. I absolutely agree with your last point though. The OP really should not be undertaking this without a much better understanding of the workings.
OP, if you keep studying Kal's site, and you get to the point where you really understand how it works and why it is wired the way it is, then consider undertaking the project. Otherwise, get some help (and it's never a bad idea to get a second pair of eyes, in any case).
Lastly, the picture you included is one of Kal's intermediate wiring steps. E.g., it does not show the seocnd hot leg, as at that point in the instructions he had yet to connect it.