Installing a 120-Volt Receptacle on a Wall Box Shelf

Turn off the electricity to the outlet you're connecting the new outlet to at your home's main electrical panel.

Unscrew the screws holding the outlet plate cover to the wall. Remove the plate cover from the outlet. Unscrew the outlet -- there should be a screw at the top of the outlet, and a screw at the bottom of the outlet -- and remove it from the wall; it will still be attached to the wiring in the wall, so pull it out gently.

Test the outlet with a voltage tester to make certain there is no electricity flowing to it. Place one lead of your voltage tester on the copper grounding, and touch the other lead to the neutral (silver), and then the hot (gold) terminals. If your voltage tester lights up when you touch either terminal, you have electricity flowing to that outlet. Do NOT proceed. Go back to your main electrical panel, turn off another breaker and test the outlet again. Do this until you know for certain the power has been cut to the outlet you are working with.

Place and hold an old-work electrical box onto the wall by the box shelf where you want to install the new outlet. Trace the shape of the old-work electrical box with a pencil and cut a hole into the wall with a drywall saw following the pattern you just traced.

Feed a 12/2 electrical cable through the wall between the hole you just sawed for the new outlet and the existing outlet. The 12 means that the wire is 12-gauge, and the 2 means that there are two insulated wires, plus a bare copper ground wire, inside the cable. Leave each end of the cable hanging out of the hole for the new outlet and your existing outlet.

Punch out the knockout holes on the old-work box with your screwdriver, and slide the one end of the 12/2 cable hanging out of the wall through the box.

Insert the old electrical box into the hole in the wall and screw it into place.

Use your wire strippers to clamp and strip 2 inches of sheathing from both ends of the cable, and a half-inch of insulation from the wires inside the cable. Bend the ends of the black and white wires into a hook with needle-nose pliers.

Loosen, but don't remove, the brass- and silver-colored terminal screws on the sides of your electrical outlet. Hook the black wire from the new cable onto the brass-colored terminal screws on the sides of the outlets and tighten the screws. Connect the white wires to the silver-colored terminal screws and tighten the screws.

Connect the copper ground wire inside the 12/2 cable to the green ground screw in the new outlet. Slide the outlet into the electrical box, and screw it into place with the terminal screws. Place the plate cover onto the outlet and screw it tight.

Cut a piece of bare copper wire about 3 inches long from an extra piece of cable.

Unscrew the ground wire from the ground screw on the original outlet. Attach one end of the 3-inch long copper wire to the ground screw. Connect the other end of the 3-inch wire and the ground wires from the two electrical cables together with a plastic connector cap.

Insert the outlet back into the wall, and screw it into place. Replace the plate cover and screw it tight. Restore the power to the circuit.