A typical well pump pressure switch has two sets of contacts for breaking both lines of a 240V supply.
But what if you have a 120V pump. Should you break both the line and the neutral with the switch or should you break only the line (and why) ?
Arky
Off the top of my head I am thinking only to break the hotwire. Although there should be a neutral lug inside the housing to complete the circuit w/ground to pump if not it is just wire nut together. Most switches have a diagram on the inside of the cover.
Maybe these will help. https://www.google.com/search?q=water+tank+pressure+switch+wiring+diagram&rlz=1T4TSNA_enUS401US438&tbm=isch&tbo=u&source=univ&sa=X&ei=gkgxVdrcM9SlyASD64GAAQ&ved=0CB4QsAQ&biw=1093&bih=471&dpr=1.25
If you can't find it there you might read this. It coinside with my answer http://terrylove.com/forums/index.php?threads/wiring-pressure-switch-for-120-volt-pump.53776/