As far as the coupler:
Cheat! Use 2 breakers that are already there. I had to add a second breaker panel in the house I just bought so I could add an ice machine and an aquarium. I replaced the dryer breaker with a 100 amp and ran the wires from it to a second 100 amp breaker panel. This gave me I think 6 more slots. I moved the dryer down to the new breaker box and have 4 left. One for the aquarium (it requires its own 20 amp breaker) and two for the ice machine (it's 220v). It was a lot of work (and money) but was required for my needs. I would suggest simply attaching the coupler to two 15-amp breakers, one on each phase. This would be 2 breakers in a row or two across from each other. Breakers are staggered to help distribute the current on both legs so that is why one side is not one phase and the other side, the other. Hopes this helps you!

Chris Couture