I realize it may have been answered but there are so many nuances I want to be sure: I have one (metal) double-gang box with one outdoor light circuit. I want to add a switch for a completely different outdoor light. The two independent circuits would co-exist in the same box. Is this legal? Should I put a warning note in the box there are two power sources (on different breakers) in the box? The obvious danger is someone switching one breaker and thinking the box is safe.
Electrical – 2 switches, 2 circuits, same box
electrical
Related Solutions
Put a divider between the two sides of the box:
Then simply label each side of the gang box as belonging to the appropriate circuit.
Note: Make sure the divider you pick will fit your gang box. I've picked up dividers that don't before.
As an answer to the last part of your updated question: If you want two separate breakers instead of a double-pole breaker, you will need to rewire from the panel to the point at which the circuits currently diverge from the 14/3 wiring so that there are truly two separate circuits without a shared neutral.
I would recommend an electrician for this type of work unless you are prepared to invest some serious time learning the NEC and acquiring the necessary permits.
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Best Answer
I mix multiple circuits in the same box a lot.
I would color the wires for the second circuit differently.
Use gray shrinkwrap or tape on the second circuit's neutrals. Then use brown or blue shrinkwrap or tape on the second circuit's hots.
If the next guy is dumb enough to mix gray neutrals with white neutrals, well, you can do what you can do, but you can't fix stupid.
I for one prefer to also use a differnt color for switched-hot (typically red), so mark the switched-hot for circuit 2 with both brown and red.