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Gangable Electrical Boxes
Some electrical boxes are gangable—meaning that with a little manipulation, single electrical boxes can be connected (ganged) side-by-side to form a double-gang box, triple-gang, or even quad-gang boxes. The classic gangable box is metal and is sometimes called a "masonry box" because metal boxes are commonly used for masonry walls. In practice, though, these gangable metal boxes are used in all kinds of construction, including traditional framed wallboard walls.
There are also plastic snap-together boxes available, but to find these you may have to shop at a specialty store that sells electrical supplies—they are not offered at most consumer building supply stores. The gangable boxes most readily available at home centers and hardware stores are the metal type, and they are fine for all applications.
Gangable boxes are available in styles suitable for new construction as well as for retro installations—this latter type is sometimes known as an "old-work" box. Make sure to buy the type you need.
The only tool required for ganging together metal boxes is a screwdriver.Continue to 2 of 4 below.
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Remove the Side Plate Set Screw
To join two or more gangable boxes together, you'll first need to remove the set screw from the side of the box that will be joined to an adjacent box. These set screws hold the removable side plates in place. Set the screws aside, because you will need them again to connect the boxes together.Continue to 3 of 4 below.
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Remove the Side Plates
On the side where you've removed the set screw, pull and twist the side plate gently until it comes free from the electrical box. On most styles, there are small interlocking bent flanges that keep the sides in place when the set screw is attached; when you remove the set screw removed, it becomes possible to pull the side plate free with a slight twist. On other box styles, the side plates may be held to the box with tabs and slots—here, you simply pull the side plate out to free it.
You won't need the side plate for the combined electrical box, so you can recycle it if you wish. Or keep it around as a spare part: Many handy homeowners have found surprising ways to put these little plates to use.Continue to 4 of 4 below.
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Join the Single Boxes
Slide the electrical boxes together with their open sides facing one another. They will have bent tabs or slots that help them fit together securely. Make sure there are no gaps between the boxes because they must create a complete enclosure to be code-compliant.
Secure the box joints with the set screws you removed earlier, and tighten them firmly with the screwdriver. The completed box is now ready to be installed.