I am changing a 2 in 1 switch that controls a light(top) and garbage disposal (bottom). They are controlled by different breakers. There was 3 wires in the old box. Black and red on top (different sides) and red on bottom, same side as black on top. I purchased a Legrand RCD33WCC6 paddle switch. When I wire red for light to top,black to common (Middle),and red for disposal on bottom. The light works with switch but disposal just comes on and stays on. What is wrong?
If they are on different breakers, you can't use a switch with a common hot.
You need something like (picked at random by Googling "dual independent switch") Decora 15 Amp Single Pole Dual Switch. The instructions include removing a tab that connects the hots if you need separate hots - just like using a dual receptacle on two separate circuits.
WAIT A MINUTE!!! From what you described, the old switch only had 3 wires! That means it also had 1 hot, 2 switched hot. In which case it was not on 2 separate breakers. If that's the case, you just have the wires confused. Separate the 3 wires. Determine which wire is hot using a tester (non-contact should be sufficient if it gives a clear indication, multimeter is the best test). Then turn the breaker (singular!) off again connect the hot to the common screw and one at a time connect one of the other wires to a switch and see what happens. You should be able to track it down that way to determine which wire goes where and get everything working.
Screw location does not have anything to do with screw function. Each manufacturer, and each model within a manufacturer, can vary.
Color does not indicate function. It should, but often it does not. If things are wired (USA) according to code, you should find:
- Green/bare = Ground
- White/Gray = Neutral
- Black/Red/other colors = Hot, Switched Hot, Travelers, etc.
So while typically black = hot, red = switched hot, there are no guarantees.