What is the NEC requirement for the depth of mud rings on outlet/switch box's? In other words, how far back from the face of the Gyp Board can the mud ring be?
I'm on an AF Base doing renovation work on housing. Base Civil Engineering is on my back about my elect. box's being too far inside the furred walls. Is it true that 1/4" is the rule of thumb?
And no, you're not being rude Mike. Thanks
Typically, what I've seen is that for 3/8" rock, the mud ring is flush with the rock. The other nice thing is that the "ears" of a device, whether it be a receptacle or switch, makes contact with the mudring, providing another ground path. If you have a separate grounding conductor, I don't think there really is any hard-fast rule about your setback. Hope that helps.
I did a code search for you, and the NEC does require that the mud-ring not be further back than 1/4" from the finished surface. My bad. Check code section 314.20.
NEC requires that no more than 1/4" of combustible material be exposed between the faceplate and the backbox. Please be careful in that this includes any wall coverings. Where thick wall finishes are used such as laminates, casework, bulletin boards, cloth covered wall panels, this 1/4" is measured from the face of the final finished surface to the box. I have gone into a finished school and pulled off faceplates only to have to make the contractor remove hundreds of device plates and go back and install box extensions. This has to do with minimizing the possibilities that a fault in the box would catch the wall finish material on fire. Where very thick wall finishes are used, it is important to have the contractor thinking about this very early in the construction process, as in some cases, it will be necessary to install extremely deep rough-in plates and in some cases deeper backboxes and this gets costly after the walls are rocked.
It is true that the Base Civil Engineer is the AHJ on the base. The NEC does limit the "setback" to 1/4", as has been pointed out in this thread. However, AF standards/regs such as UFCs, AFIs, ETLs, and TOs often dictate overkill, whereas the NEC is always the minimum. Working on an AFB myself (civilian), in CE, I'm willing to bet, if asked, the BCE Project coordinator would be happy to share information with you if asked.
Boxes are supposed to be flush with the back of the gyp board. Plaster rings are availabel in standard depths matching the standard thicknesses of wall board.
I have seen contractors use 1/2" extension rings with 5/8 wall board and claim it was ok because it was within an 1/8 inch. The job was kicked over as it should have been and they were told to use the right rings. One part of the electrical inspection should have been made before the gypboard went up. If it was caught then it should have been flagged. Someone using the wrong rings is doing something wrong and probably more than just wrong rings. If I were inspecting the job I would start watching the guy like a hawk. I would cost him more money than he saved by using the rings he had in back of his truck or whatever.
If you have a gap it makes it easy for someone to take a piece of wire and push it between the faceplate and the box. Of course that kind of thing never happens.
mpparent: Whether or not the NEC is applicable really depends on where you're working. Usually facilities will be built to NEC or relavant mil-spec, whichever is more restrictive. I mean, we don't exactly call the local building inspectors down to check the installation, but you'd be hard pressed to find an instruction authorizing you to ignore all local laws. I know whenever we write up a contract, we ALWAYS specify NEC right in there; I bet if you looked hard enough, you'd find this to be the case almost universally.
If you're on a ship or aircraft or something exotic, then all bets are off, though, and it usually ends up at an authorizing engineer's discretion to do whatever he feels like.
