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I have installed a back splash in my kitchen, if I use the plastic spacers how many should I use or is there a limit? I understand that this can cause to much air space around the receptacle or light switch.

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A picture of the situation would be very helpful here. Are you saying that the new back-splash went up higher than the existing outlet openings and now the outlet boxes are recessed by the thickness of the back-splash material? – Michael Karas May 30 '13 at 8:35

If your problem is that the thickness of the back splash material has caused the electrical boxes to become recessed you may need to use electrical box extenders. These come in a number of styles depending on the type of electrical boxes you have. There are options for metal or plastic boxes for starters. Other factors would be amount of extension needed and whether you are dealing with a single width type box or a wider type.

Here is an example of a metal box extender that works in a telescopic manner to accommodate just the amount of extension that you require.

enter image description here

If you're in an area that follows National Electrical Code (NEC), the boxes cannot be set back more than 1/4" (6 mm). If the backsplash has caused the boxes to be set back more than this, you'll have to use extenders to bring the box out to the proper depth.

National Electrical Code 2011

ARTICLE 314 Outlet, Device, Pull, and Junction Boxes; Conduit Bodies; Fittings; and Handhole Enclosures

II. Installation

314.20 In Wall or Ceiling. In walls or ceilings with a surface of concrete, tile, gypsum, plaster, or other noncombustible material, boxes employing a flush-type cover or faceplate shall be installed 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.).
In walls and ceilings constructed of wood or other combustible surface material, boxes, plaster rings, extension rings, or listed extenders shall be flush with the finished surface or project therefrom.

If the box is less than 1/4" from the finished surface, you can use as many spacers as needed to mount the receptacle in such a way that the yoke is held rigidly at the finished surface.

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Exactly what I used when I installed my back splash. I had no issues and it help to solidify the outlet. – Maxime Morin May 30 '13 at 13:23
hopefully, the ears will rest on the tile and you won't need the spacers, just longer screws. The extenders will partially mitigate air migration, but there are die-cut foam sealers to block airflow – HerrBag May 30 '13 at 22:10

You use as many spacers as needed to get the outlet/switch mounting tabs flush with the tile. You may not need them if the mounting tabs of the box extender suggested by Mr Karas are tall enough to hold extender and device (just need longer screws: 6-32, in either case )

enter image description here

Die cut wallplate insulation gaskets: they go over switch/outlet and under wallplate. They block airflow by sealing around box perimeter and fit tight around device.

The adhesive is good for 1 shot and then will need replacement.

enter image description here

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Those spacers should come with a printout of a couple important code sections. I've pasted the verbiage over in chat. It basically says that if your box is set back more than 1/4", you need an extender. – Tester101 Jun 5 '13 at 19:10
Agree that extender > 1/4 is needed. You may need the spacers to support the extender when hole is overcut. – HerrBag Jun 6 '13 at 16:52

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