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When placing the blue Carlon (non-adjustable) PVC outlet & switchboxes on 2x4 studs, they have alignment tabs that allow proper depth for 1/2" drywall. Several have been set using the tabs.
We are now switching to 5/8" interior drywall throughout.
What is best practice, to simply line up with the box alignment tabs or should I extend the box out another 1/8" to the full 5/8" depth?
If you're installing new boxes or otherwise need to adjust existing boxes, by all means set them in the right position. However, if the existing boxes were well-placed originally it may not be necessary to do any additional work to bring them to the new drywall surface. From 2017 NEC:
314.20 Flush-mounted Installations.
Installations within or behind a surface of concrete, tile, gypsum, plaster, or other noncombustible material, including boxes employing a flush-type cover or faceplate, shall be made so that the front edge of the box, plaster ring, extension ring, or listed extender will not be set back of the finished surface more than 6 mm (1∕4 in.).
Installations within a surface of wood or other combustible surface material, boxes, plaster rings, extension rings, or listed extenders shall extend to the finished surface or project therefrom.
Proper support from behind is important especially for devices like receptacles which see pushing-into-wall forces during plug insertion. Face plates can break when they're called upon to resist those forces. Ideally the drywall is trimmed close to the box so that the ears of the device yoke rest on it. When the drywall support is insufficient shims should be placed on the device mounting screws so that the device is held snug. Then forces transfer from the device, through the shim, into the box.
Whether the set back is the maximum 1/4 inch or something minimal like 1/16 inch this support is important. When the set back is small enough that an extension ring doesn't fit, or when an extension ring reduces the gap but doesn't quite make things snug, shims on the mounting screws are the way to go.
There are lots of options such as spacers, extenders, and mud rings.
At the end of the day you will probably save the most money and time by finding an 1/8" shim and placing it behind the alignment tabs when nailing your receptacle boxes.
When installing boxes on studs without drywall in place it seems to me that laying a 1.5 inch wide piece of material the same thickness as the intended finish wall against the face of the stud would allow correct positioning of the boxes.
I can imagine an electrical supervisor lightly stapling a piece of drywall or other material of the correct thickness on the stud at each box location, and instructing the installers that they are to have the outside edge of the box lined up with that and leave it in place for removal at the pre-inspection check, or for the official inspection, or even for the drywallers to remove.
EDIT I can also imagine a jig that would hold a sample of the finish wall material against the edge of the stud and have an edge to which the electrical box would be pulled to position the edge flush with inside of the finished wall.
EDIT' The ears on the ends of the tabs of switches and receptacles have holes to allow them to be used as shims through which the screw passes. If the box is set back into the wall, snap off the ears at the score marks and put them on the screws. Use one, two or more as necessary to get the device tight to the box and at the correct position relative to the finished wall.
If the boxes are metal, the metal shims make electrical contact for the ground. If the device has paper keepers on both screws, then at least one must be removed to allow grounding. Good quality devices intended for use onmetal boxes have a metal keeper on one end.
Just had to do the same thing when we chose to go with 5/8” fire-retardant drywall after installing these same 1/2” deep receptacles. I was about to make a shim, but just discovered the easiest way for me to bump them out was to take them off the wall, hook each outside tab against the 5/8” mark on my speed square then mark at the pivot point. Use the straight line to line up against the stud. (For any future perusers)
