sharrisct25 The XPS3-IW is the Pro version of the WS13A. I don't have a XPS3=IW to look at but I believe that the terminal hookups on the back are the same. Either of these switches are designed to work in a single switch application or a 3 or 4 way application. The 2 top connections on the switch marked "CONTROL" are for using the switch in a 3 or 4 way application and is not used when using the switch as a single stand-alone on off switch.
You should have a hot lead, or power into the switch box wired to the terminal marked "LINE". Your white, neutral wire, going to the switch terminal marked "NEUTRAL" and the line going out to your pool pump (should be black) hooked to the "LOAD" terminal on the switch. The white wire coming from your pool pump can hook into the second terminal on the switch also marked as "NEUTRAL".
If you can tell me the number of wires and there colors that are going into the switch box I should be able to draw up a little print of whats going on. Also are you replacing an old switch with this X10 model and is this, did this, turning on and off an outlet out by the pool and the pump plugs into that? Also are there bare ground wires in the box and what are they connected to?
The GFI breaker shouldn't trip with just the addition of the switch unless there is some leakage to ground some where. (wouldn't take much) Does anyone know of a wiring print for the internal electronics for a XPS3-IW or a WS13A?
I posted this before reading your reply post so some of the question you have answered.