How to Install an Electrical Box in an Insulated Wall

Measure the distance from the floor to the center of the intended electrical box and mark it with a pencil. For example, if the box is for a switch, you may want the toggle centered 48 inches from the floor. If the box is for an outlet, 18 inches to the box center is appropriate.

Hold an old work electrical box against the wall and center it on the pencil mark. Place a torpedo level on top to check its positioning. Trace the electrical box outline onto the wall with the pencil.

Install a drywall screw into the center of the box pattern. Tighten the screw halfway into the drywall with a Phillips screwdriver.

Cut along the pattern lines using a utility knife. Do not try to cut entirely through the drywall on the first pass. Accuracy counts, so keep the knife on the line and make added passes as necessary.

Grip the drywall screw on the last cutting pass and pull the drywall plug out from the wall.

Drill a hole in either the top or bottom plate of the wall, depending on where the ROMEX® cable is coming from. A drill fitted with a 1/2-inch brad-point wood bit must be used to bore the hole as close to the interior drywall as possible.

Wrap the hooked end of the fish tape with several turns of electrical tape to prevent a snag on the insulation in the wall cavity.

Push the fish tape through the plate hole positioning it between the insulation and the back of the interior wall. Have a helper at the wall box opening to retrieve the fish tape.

Attach the second fish tape to the one in the wall and tape around the hook as in Step 7. Pull the fish tape hooks to your location.

Disconnect the two fish tapes and connect the ROMEX® cable to the fish tape from the box hole. Bend the conductors into a loop and secure them to the fish tape hook. Wrap the loops with electrical tape.

Pull the ROMEX® cable to the box hole. The helper can pull the cable attached to the fish line as you push from the other end. The cable will pass between the wall and the insulation without snagging.

Disconnect the ROMEX® from the fish tape hook at the box hole.

Insert the cable into the slot of the old work electrical box. Place the box into the wall and tighten the two wing-anchor screws clockwise with a screwdriver to secure the box to the wall.