These days I was changing my pool pump controller and I had to call FPL for their On Call box that is connected before my pool pump. As it tunred out they still don't support these boxes when you want to install a electronic pump controller.
Anyway I had some problems figuring out the wires before that. I was left with the impression that the entire box is entirelly between the input lines and the pump. It turned out it's just cutting one of the lines.
There are 3 wires - Black, Blue and Red. So the black one is the line that is not interrupted or I assume that if it's a single pahase (120V) this will be the neutral.
The red one is the input for the other line that the box will cut if needed. And the blue wire is the output of the iterruptes line.