The wall is 2" thick (tile, mortar, some sort of backer board/drywall), the cavity is is ~5 1/2" deep from the face of the tile to the back of the wall cavityWhat is 2"? The thickness of the wall, the cavity, or the distance from the face of the wall to the back? There are some specialty boxes that are available.
I am using a GFCI, I got a 3 1/2" deep old work PVC box, but the tabs only go back 1 1/2" so it wont reach behind the mortar to clamp. Longer screws will push the tab way past the track they ride in that keeps them vertical.There are plenty. It's going to require a trip to the nearest box store. Don't forget that all kitchen counter receptacles are supposed to have GFCI protection. I don't think a GFCI receptacle will fit in a shallow box, but I've never tried.
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Carlon 1-Gang 8 cu. in. Electrical PVC Shallow Flanged Old Work Electrical Switch and Oulet Box (B108R-UPC) B108R-UPC - The Home Depot
Safely split and branch into different directions with the selection of this Carlon Blue PVC 1-Gang Flanged Shallow Old Work Electrical Outlet Box.www.homedepot.com
https://www.homedepot.com/p/Carlon-...ical-Switch-and-Outlet-Box- 117RSWR/202077341
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1-Gang 17 Cu.In. Shallow PVC Old Work Electrical Outlet/Switch Box
1-Gang 17 Cu.In. Shallow Old Work Electrical Outlet/Switch Boxwww.menards.com
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RACO 1-1/2" Galvanized Steel Electrical Switch/Outlet Box
The RACO® two-by-three-inch, one-gang Galvanized Steel Electrical Switch Box is 1-1/2 inches deep and non-gangable. Switch boxes are used to house devices such as switches or outlets.www.menards.com
Metal box with Madison bars. No wall anchors needed.I am using a GFCI, I got a 3 1/2" deep old work PVC box, but the tabs only go back 1 1/2" so it wont reach behind the mortar to clamp. Longer screws will push the tab way past the track they ride in that keeps them vertical.
I saw the metal boxes with the plaster ears, but I don't think there is enough tile to drill and use wall anchors, plus the GFCI wouldn't fit in the box, the ground screw stuck out to far and hit the bottom of the box
I misunderstood the original post, you explained it while I was making my post.I am using a GFCI, I got a 3 1/2" deep old work PVC box, but the tabs only go back 1 1/2" so it wont reach behind the mortar to clamp. Longer screws will push the tab way past the track they ride in that keeps them vertical.
I saw the metal boxes with the plaster ears, but I don't think there is enough tile to drill and use wall anchors, plus the GFCI wouldn't fit in the box, the ground screw stuck out to far and hit the bottom of the box
I've seen long Madison bars that would work with two layers of drywall, but I don't think they would work with 2" wall covering. I have the standard depth on my van and I know they won't work.Metal box with Madison bars. No wall anchors needed.
Most are 1.5”. But the photo I posted are 2.5”. That might work. But if a stud is there a smart box would be good.I've seen long Madison bars that would work with two layers of drywall, but I don't think they would work with 2" wall covering. I have the standard depth on my van and I know they won't work.
The Allied box looks like it may work with that style of clamp on the back, Thanks!I misunderstood the original post, you explained it while I was making my post.
Use longer screws for the pvc box? I'd get one of these and use a longer screw. I do it with old work light boxes all the time. You could also shorten the bracket with some snips.
Allied Moulded FiberglasBox Old Work 16 cu in Square Fiberglass 1 gang Outlet Box Beige Mfr# H9361=ESK - Ace Hardware
Single gang electrical box for use with non-metallic sheathed cable.Find the BOX SGL GNG FBGLS 16CU at Ace.www.acehardware.com
I was concerned the screws wouldn't go into he studs to well due to the wall thickness, but I'm thinking I could mount that box further back so it screws into the studs and add a box extender to bring it flush with the wall.![]()
Southwire Smart Box 1-Gang Adjustable Depth Device Box MSB1G - The Home Depot
Visit The Home Depot to buy Madison Electric Products Smart Box 1-Gang Adjustable Depth Device Box MSB1Gwww.homedepot.com
If you're on a stud, just get a regular nail on box, remove the nails, and cut the nail slots off. Then you can run your own screws through the side wherever you want to. I was doing that years before I ever saw the screw on type box.I was concerned the screws wouldn't go into he studs to well due to the wall thickness, but I'm thinking I could mount that box further back so it screws into the studs and add a box extender to bring it flush with the wall.
I just found this while googling box extenders, it looks like it extends the old work tab guides too so it might work with my original old work box I was trying to use
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Carlon B1MGEXT-2 Box Extender, 3-1/4 in L, 2-1/4 in W, 1-Gang, PVC, Bl
Extends an existing box by 1-1/8 in. Used to correct problems from remodeling where the wall surface is extended. Fits between the wiring device and the wall surface. Extends the switch or outlet box to flush with the wall. Works with all standard wiring devices. 2-1/4 in x 3-1/4 in. UL...www.shelllumber.com
Sometimes ya gotta do whatcha gotta do. It probably shouldn't be done with a fiberglass box though.Technically ( I hate to cite code amongst professional electricians, but the homeowners must be made aware), screws aren't allowed inside a box unless it was designed for them like the example above. Have I ever used screws from the inside? I'll plead the 5th.
Fixed it for you. The screws don't enter the standard plastic/pvc/ fiberglass boxes. Some metal boxes and mud rings, yes, but drywall screws don't work worth a pinch of **** in those anyway. Gonna have to use longer 6/32's on those.Now that you bring that up, no pointed end screws should be used on any device if they enter any enclosure containing wires. Again, for the posterity should those reading in the future come across this thread about attaching a box.
You said device. How many devices mount to panels? I see pointed sheet metal screws in panels all the time, but I don't do that one. I find it funny when a home inspector takes them out and won't put them back in. I keep a bag of Square D panel screws on hand for those $150 jobs. A Siemens or Eaton panel may not be listed for a SQD screw, but they fit.I was thinking of non blunted sheet metal screws on some panels where they don't go outside the panel.
Good find.I just found this while googling box extenders, it looks like it extends the old work tab guides too so it might work with my original old work box I was trying to use
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Carlon B1MGEXT-2 Box Extender, 3-1/4 in L, 2-1/4 in W, 1-Gang, PVC, Bl
Extends an existing box by 1-1/8 in. Used to correct problems from remodeling where the wall surface is extended. Fits between the wiring device and the wall surface. Extends the switch or outlet box to flush with the wall. Works with all standard wiring devices. 2-1/4 in x 3-1/4 in. UL...www.shelllumber.com
VS. 
I use a thread insert, Heli-Coil is one brand, on plastic boxes so that the OEM screws can still be used.Sometimes ya gotta do whatcha gotta do. It probably shouldn't be done with a fiberglass box though.
Using a drywall screw in place of a 6/32 to install a device is also a code violation but I've done it and so has everyone else.
I've never seen heli coils that small, but never looked either. I haven't used very many drywall screws for devices, usually on a worn out fiberglass box, but I think every smoke detector I have ever installed (1000's) has been mounted to a single gang box with two 1-1/4 drywall screws.I use a thread insert, Heli-Coil is one brand, on plastic boxes so that the OEM screws can still be used.
Not easy to find, needed 8-32 inserts for a Rockwell 1"X42" sander grinder that a screw holding the motor fan shroud had sheared off on & finally found it at one of the local NAPA branches. Not sure I have enough of the sanders though, have 3 1/2 of them, & hard to find parts for.I've never seen heli coils that small, but never looked either. I haven't used very many drywall screws for devices, usually on a worn out fiberglass box, but I think every smoke detector I have ever installed (1000's) has been mounted to a single gang box with two 1-1/4 drywall screws.
Just for completeness, here is the link to deep Madison bars. As always YMMV.I've seen long Madison bars that would work with two layers of drywall, but I don't think they would work with 2" wall covering. I have the standard depth on my van and I know they won't work.