electrical
I need to increase the cu/in (inner space) of a switch.
So I'll switch from 1 gang to 3 gang, and place the switch back in.
After replacing a 1-gang electrical box with a 3-gang box, am I allowed use the same 1-gang wallplate and drywall over the rest of the box?
Basically It would cover with drywall, the other 2 "gangs".
(I would have to recess it in more, and use longer screws)
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.
There are boxes that you can use that has the partition in them to keep the interference down. The trick, possibly for you is to make sure the lines where they run parallel with each other is keeping them separated at a MINIMUM of 6". The low voltage guys I have worked with preferred 12" and more, some wanting 2' separation. If the walls are still open it should not give you no trouble then. When you do pass by a line voltage wire, use an extra foot or two and run the low voltage across the line voltage at a 90 degree angle, this will minimize the "crosstalk" where the cables meet.
Best Answer
No, you can't box a box in like that!
When you have a multigang box, all the innards need to be accessible without removing any building finish, as per NEC 314.29, so that the next bloke who services the thing can get at all the stuff inside. Your choices are to either use a 3-gang to 1-gang mudring (as was linked in the comments), or to use a 3-gang cover that has blank spaces (i.e. no switch or receptacle openings) in the other gangs.