I live in the US and have the Twist Lock Electrical Plug 4 Wire, 30 Amps, 125/250V, NEMA L14-30P. It has 2 hots, 1 ground, and 1 neutral wire. I saw the following scr controller on ebay and am confused how one might do the wiring. There's a wiring diagram on the side of the picture.
Am I supposed to combine 2 hots IN, shared neutral for both IN and OUT (COM slot), and 2 hot wires from OUT?
I'm used to the controllers that have 4 slots, 2 hots IN and 2 hots OUT.
You are correct - this is European style, where they run 220 instead of 120, so they only need one phase - a hot and a neutral. Here we use two phases (2 hots) for 220, so you can't get there safely. See if the seller makes a US version.
That is a single-phase controller as clearly indicated by the diagram on the side. From your "2 hots" description it sounds as though you have a two-phase + neutral supply. If you combine two hots in you will short circuit the phases together.
You need to either get two of these - one for each phase - or get a two-phase controller. If getting two the control side inputs can probably be wired in parallel but you haven't provided enough info to assess that fully.
simulate this circuit – Schematic created using CircuitLab
I have the device in use as a controller for a 120 volt quartz tower heater. The unit is designed to be in series with the load and is in reality a two terminal device the common terminal being unused in the circuit (thus the broken line on the diagram). The common terminal is just a tie point so you don't need a wire nut. For 220v use just consider one line as a return.
