Installing an Electrical Box in a Finished Wall

Intro

Running cable through walls covered with drywall or plaster is difficult. Plan the job carefully before starting.

Remodel boxes (also called cut-in or old-work boxes) clamp to the drywall or plaster rather than attach to a framing member, making the work easier. However, they are only as strong as the wall surface to which they are clamped. If the drywall or plaster is damaged, cut a larger hole and install a box that attaches directly to a stud or joist. Select boxes that meet local codes. For a ceiling fan or a heavy light fixture, buy a fixture box that attaches to a fan-rated brace.

Before cutting a hole, use a stud finder to make sure no joist or stud is in the way.

Checklist

Time
About 15 minutes to cut a hole and install a remodel box (not including cutting a pathway for the cable and patching walls)

Tools
Stud finder, torpedo level, utility knife, screwdriver, hammer, drill, drywall saw (or rotary cutter or jigsaw)

Skills
Measuring and cutting drywall

Prep
Carefully plan the routes for the cables and the locations for the boxes. Spread a drop cloth or large towel on the floor below.

Materials
Remodel boxes acceptable under local code, cable clamps, if needed

Previous | Next

Other Remodel-Box Options

The round plastic ceiling box (left) has "wings" that rotate out and behind the wall surface. One metal box (center) has a flange that springs outward when the box is inserted; tightening a screw brings the flange forward. A variation on this has side clamps that move out and toward the front as screws are tightened. Yet another type (right) uses separate mounting brackets that slide in after the box is inserted and bend over the sides of the box to lock it in place.

Step 1

If the box does not come with a cardboard template, hold its face against the wall, use a torpedo level to make sure it is straight, and trace it. With a utility knife cut the line deeply enough to cut through the drywall paper.

Previous | Next

What If the Wall Is Made of Plaster?

Take your time cutting a lath-and-plaster wall -- it's easy to damage the surrounding area. Most plaster is attached to 3/8-inch-thick wood lath, which cuts fairly easily if it does not vibrate. If it does vibrate as you saw, sections of plaster can loosen from the lath. It is difficult to make a neat hole in plaster and lath, so have patching plaster on hand. If plaster is attached to metal lath, cut all the way through the plaster with a knife and then cut the metal lath with side cutters.

Make several passes with a sharp knife. Drill starter holes at each corner and then cut with a jigsaw. Press the saw firmly against the wall to minimize lath vibration.

Alternatively use a rotary cutter equipped with a plaster-cutting bit. Practice first because it is hard to control.

Step 2

Cut the hole with a drywall saw. Cut to the inside of the knife cut to prevent fraying the paper. Test to make sure the box fits in the hole.

Previous | Next

Step 3

Run cable through the hole. Strip 8-12 inches of sheathing and run the cable into the box. Whichever clamping method the box uses, 1/2 inch of sheathing should show inside the box. Tug to make sure the cable clamps tightly.

Previous | Next

Step 4

Push the box into the hole. If it fits tightly, do not force it or you may damage the drywall. If needed use a utility knife to enlarge the hole.

Previous | Next

Step 5

This type of box has wings that extend outward when you start to drive the screw, then grasp the back of the drywall as the screw is tightened. Tighten the screw until you feel resistance and the box is firmly attached.

Previous | Next

Comments