Can I wire a doorbell transformer in-wall this way?

Question

My current under-powered doorbell transformer is in a very awkward location (old home, etc.) and in a location where several old wires are cable-nutted together and I would rather not replace it there. I can disconnect and patch through the existing LV wiring easy enough though and I have a much more accessible location to install an updated one. However-

The location is in a coat closet, with an existing (currently capped) 120vAC line and close proximity to the doorbell wiring. But it is waist-high and would be covered by coats all the time. Would that be a problem if I surface-mounted the transformer?

What I’d like to do is mount the transformer in the wall cavity. I know code requires this to be accessible so I can’t drywall over it, but can I have a transformer like that attached to a gang box on its side, with all of the wiring behind a cover plate? Or cover plates?

As seen here the 120v is behind the existing wall plate in a single box currently mounted on a stud. (Green). The doorbell wire runs vertically in the same wall cavity (red area) and has enough slack to reach the green area easily.

So- do I just expose the transformer at waist height and surrounded by coats, or can I put the whole mess in the wall and cover it appropriately (vented panel?). I’m in Virginia and would like to do this to code. Thanks!

Answer 1

The line voltage parts of the circuit must be contained inside an electrical box which has an accessible cover. The low voltage wires should not be inside the electrical box.

If I were doing this I would make a new opening for an old work electrical box up near the ceiling of the closet. Then drop a new electrical cable down the stud cavity from the new opening and enter into the existing electrical box (it may turn out to be easier to push the new cable through the existing electrical box up the wall to the new opening where you can reach in and snag the new cable). Once the new box is all installed in place you can mount the new transformer on the box cover of that new box with the low voltage wire terminals being up near the ceiling.

Before you start do check that wall cavity to see if it has a cross member or fire block that would impede pushing the cable up the cavity. If so it may be necessary to make a temporary hole in the drywall near the blocking so that you can drill a hole through it for the new cable.

The new cable used must match the wire gauge of the existing wiring in the low down electrical box.

Answer 2

I would not assume that just any transformer can be stuffed in the wall, some will heat up and won't last long. Select one like for example the Edwards Signalling 591 which is rated for use inside a box. They even make a mounting plate part 593 which serves as a separator, which would allow you to put the transformer inside a 2-gang box with the power.