How to Install an Electrical Box in an Existing Wall

Tape Old-Work Box to Wall Backwards

Many of these old-work boxes from home centers and other big home improvement stores do not come with paper templates. Either you make your template, transfer measurements to the wall with a ruler, or use the box itself as a template.

Because these boxes taper from smaller to larger, you cannot use the back sides as templates. Fortunately, you can use the face as a template, since the face is flat.

Tape the box to the wall with painter's tape, face-first. Apply tape to the top and bottom. It's not necessary to tape the sides. If you have an assistant, there's no need to tape the box. Just have the assistant hold the box firmly against the wall as you draw the outline.

Mark the Box's Horizontal Lines First

Because of the uneven outlines of most old-work electrical boxes, it's not easy to simply draw four pencil lines around them. You'll need to draw lines where you can find them and then fill in the missing parts.

• First, mark horizontal lines where the tabs meet the box. The tabs are the flat pieces that press against the wall from the front, creating tension in conjunction with those back wings.
• Use a mechanical pencil or well-sharpened regular (not carpenter's) pencil, because you need a sharp, precise line. Do not use a ball point or ink pen, as it can be difficult to cover the marks.
• You need to get these lines right, or the box will not stay in place; it will fall back into the wall.

Mark Outlet Box's Vertical Lines

With the horizontal lines marked, draw two straight vertical lines down the sides of the old-work box. While you should try to be precise, these are less critical because there are no tabs on the sides.

Connect Lines for Box Cutout

Remove the box from the wall. With your straight edge, connect horizontal and vertical lines to make a complete outline. 

Make Precise Box Cutout With Jab Saw

Before you make your cut-out, drill a hole in the center of the outline with a 1/2-inch auger bit. Now, use your manual jab saw to cut the outline. Be extremely precise about this, preserving your line as you cut with the saw rather than cutting right on the line. 

If you have an assistant, let the assistant hold a shop vacuum nozzle under the saw as you cut. This does not completely rid your area of drywall dust but it does significantly help cut down on it.

Grab Cutout Before It Falls

Before you finish your last cut, poke a finger into that 1/2-inch hole and hold onto the cut-out so that it does not drop into the wall. It makes for a cleaner, neater job if you can retrieve it.

If you forgot to make the hole earlier, you can try to grab the side of the cutout with the teeth of the jab saw.

File Sides of Cutout to Widen

While a perfect cut-out is ideal, it's always better to have a hole that is too small than too large. If the hole is too small, use your jab saw to file down edges until the box fits carefully. Do not try to cut away slivers of drywall. Instead, just use the saw as a kind of sanding tool to slough off gypsum to widen the hole.