Use a 20amp double pole switch. The intermediate switch could be used at a push as you are not switching a huge load. The intermediate will probably be rated at 10 amp. If you do use this then put your blues in a connector and put one brown into the top of the switch and the other in the bottom. If it does'nt work move the bottom brown to the other terminal. I'm not sure which terminal an intermediate switches to at the bottom. I would use the 20amp double pole switch though