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I have a 3/4" thick man made quartz backsplash in the kitchen. The electrical box cut outs are not quite big enough for the box extender. The electrician says I need the box extender and that the backsplash guys often have to trim their installs for them to fit. The backsplash guy says he has done 100s of houses and never had to trim a cut out for an electrician.

Is this a code requirement if so what is the idea behind the code? Is it a fire concern since the box could have an air gap between the backsplash and the drywall. Could I fill that with a fiber reinforced drywall setting compound?

There are two 3 gang cut outs in this installation. I tried a silicon carbide grinding stone in a 1/4" 20k rpm air grinder which did very little material removal. I also tried a rotozip XB-FTC1 which also did very little.

The box behind the quartz backsplash is a grey electrical box. The electrican has tried to use the Arlington BE-3 which when forced into the hole is distorted in the horizontal direction as the cut out is not wide enough to accomodate the box extender.

I did have the backsplash guy come out and I had an angle grinder with a 3 3/8" blade. He couldn't think of what tools he could use to do it so he gave my tool a try. The blade did a good job cutting into the sides but then the backsplash guy wasn't sure how to safely cleanup the corners so he said he'd think about what tools he could use. He also marked up the backsplash a bit with the grinder blade protector and gashed the quartz a bit outside of his cut which is hopefully still going to be hidden by the cover plate.

Given the electrical code issue pointed out below by NoSparksPlease what should I do? I could try the XB-FTC1 in my 30k dewalt cut out tool but given the very small amount of material that was coming off via the die grinder I think it would take hours. Any tool recommendations to cleanup the corners where the angle grinder couldn't get without over cutting the hole?

I'll re-post the hole cleanup / recommendation question separately as I've received the code question answer.

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    You are the one paying for the back splash, if you want a larger opening the the backsplash for a properly fitting outlet then tell the backsplash guy if he wants your money to do as you say. – Alaska Man Jul 7 '20 at 18:38
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    You need box extenders when there is flammable material proud of the box, e.g. a plywood veneer put over a box already set properly into the drywall. The flammable material isn’t the quartz, but it might be something behind the quartz, and this may be fairly unique to this situation. Also, the electrician may be using an unusual size of box extender. As always, if you want something done right, you have to don the Infinity Gauntlet and deal with the Avengers... – Harper - Reinstate Monica Jul 7 '20 at 19:24
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    I would say that the right word is combustible rather than flammable; the difference being, basically, able to be set alight vs. easily set alight. If the quartz backsplash is mounted directly to the drywall, and the box is mounted normally (flush with outer surface of the drywall), don't worry about using an extender, just get longer screws. – Jimmy Fix-it Jul 7 '20 at 20:16
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    There are some flexible white plastic extenders which might fit where the rigid blue plastic ones will not. – Jim Stewart Jul 7 '20 at 20:53
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    Are the underlying boxes plastic or metal? That's often the determiner as to what to use for an extension ring.... – ThreePhaseEel Jul 8 '20 at 0:07
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I don't know what all the issues are that influence the code, but here is what it says:

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.).

If your electrician is trying to fit an Arlington BE-1 which often does not fit well maybe he could try a Raco 976.

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    Thanks ! This is for (2) 3-gang boxes so he was trying to use the BE-3. Looking at the backsplash vs the box, the top and bottom of the quartz line up well. The sides are off by 1/8" on each side. – Fresh Codemonger Jul 7 '20 at 21:05

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