I’d like to add a on/off switch to my well water pump which is located in my basement. I plan on putting the switch at the top of the staircase in case of basement flooding. I plan on tapping into the load line going into the pressure switch. Is there a way to add the switch by only running one Wire from switch to the box where I’m tapping into, or do I have to run two wires. It’s a 20 amp 240v pump so I’m using 12/2. I assume if one leg stays tied together and I switch the other leg that the pump would still be getting current and it would not work.

thank you