How to Add an Electrical Outlet

Turn Off the Power

At the main service panel, shut off the power controlling the circuit that serves the electrical outlet from which you'll be feeding cable for the new outlet.

Use a non-contact circuit tester to verify that power is off at the outlet.

Extract the Existing Outlet Receptacle

At the existing outlet that will feed the circuit extension, remove the cover plate, then loosen the mounting screws and extract the receptacle from the box. Try to leave the wire connections intact, but gently pull the receptacle to one side so you have access to the inside of the box.

Examine the receptacle and its wire connections. Ideally, the feed wires should connect to silver and brass-colored screw terminals on opposite sides of the receptacle, leaving an open pair of screw terminals. These open screw terminals will accept the wires from the new cable that will feed your new outlet.

If the wiring configuration seems more complicated than this, it's a sign that you may want to hire an electrician to complete the work.

Also examine the electrical box. It should have several openings through which a new cable can secured. The method for securing cables will vary depending on the type of box, In some cases, it may require an additional metal cable clamp, but other boxes have built-in clamps.

Remove the Baseboard Trim

Draw a fine pencil line along the wall at the top of the baseboard, from the existing outlet to the new outlet location. This line will serve as a reference for the following steps.

Use a utility knife to slice through any paint sealing the joint between the baseboard and wall. Use a putty knife and small flat pry bar to carefully pry the baseboard away from the wall. Be careful, as old baseboards can be brittle and prone to cracking.

Remove the nails from the baseboard and set it aside.

Remove the Drywall

Using a drywall saw, cut away a long strip of drywall just below the pencil mark. Be careful not to cut too deep, as you could cut a wire hidden behind the drywall. Carefully pull the strip of cut drywall away from the wall. Set it aside so that you can reinstall it later.

Cut a Hole for the New Outlet Box

Mark the desired location for the new outlet box on the wall. It should be at the same height as the existing outlets in the room—normally about 12 inches from the floor to the bottom of the box. You will be using an "old work" retrofit electrical box, so the new outlet is best positioned midway between wall studs. Position the box against the wall, using a level to ensure it is level, then draw a pencil outline around the box on the wall.

Use a drywall saw to cut out the drywall along the marked outline.

Drill the Studs

Using a drill and a 3/4-inch spade bit or auger bit, drill holes through the centers of the studs, just above the floor plate.

Run the Cable

Measure and cut a length of NM cable to run from the existing outlet to the new outlet, through the holes drilled in the studs. Allow about 1 foot of excess cable at both wall boxes. (A 15-amp circuit calls for 14-gauge wire; 20-amp circuits use 12-gauge wire.)

Beginning at the new outlet location, run cable down through the wall opening, then through each drilled hole in the stud, up to the wall cavity where the existing outlet is located.

Feed Cable into the Existing Box

Feeding the new cable into the existing box is one of the trickier parts of this project.

One of the easiest ways is to extend a fish tape down through a knockout opening in the electrical box down through the wall cavity to a point where you can secure it to the new cable with electrical tape. Then, pull up the fish tape, drawing the cable through the knockout opening and into the electrical box. Pull 8 to 12 inches of cable into the box, then secure it in place using the internal cable clamp or locknut.

Install the New Box

With cable secured at the existing outlet location, return to the cutout opening for the new outlet, and thread the cable into the new old-work electrical box. Make sure you have at least 8 inches of excess wire extending into the box. Secure the cable to the box with the internal cable clamp.

Insert the box into the cutout opening, and secure the box in place with the retention tabs attached to the box, or with Madison straps.

Connect the New Outlet

• Use a cable ripper to cut into the outer jacket of the cable, beginning about 1/2 inch past where it enters the box.
• Use a utility knife to carefully cut away the loose jacket.
• If necessary, trim off the black hot wire, the white neutral wire, and the bare copper grounding wire to a total length of about 8 inches.
• Strip 3/4 inch of vinyl insulation off the tip of the black and white wires.
• Use needle-nose pliers to form a small C-shaped loop in each wire, then attach the black wire to one of the darker, brass-colored screw terminals on the side of the receptacle.
• In the same manner, connect the white wire to a silver (neutral) screw terminal on the opposite side of the receptacle. Connect the bare copper grounding wire to the green grounding screw on the strap of the receptacle.
• Tuck the wires into the box and attach the receptacle to the box with its mounting screws.
• Install the cover plate and you're finished with this outlet.

Connect the Existing Outlet

If you see that there there is an empty brass hot screw terminal and an empty silver neutral terminal on the existing receptacle, then the new cable can be stripped and its wires attached to these screw terminals (white wire to silver terminal, black wire to brass terminal). The bare copper grounding wire, however, will need to be joined the existing grounding wires by detaching the grounding wire from the receptacle and adding a short bare copper pigtail wire. All the grounding wires entering the box, as well as the receptacle's pigtail, are joined together with a wire connector.

But if all screw terminals on the receptacle are being used, then you will need to detach all wires and use short pigtail wires and wire connectors. This involves cutting scrap pieces of black, white, and bare copper wire, then using wire connectors to join the receptacle and the new cable extension to the corresponding existing circuit wires.

When the wire connections are complete, gently fold the wires into the box, attach the outlet to the box with its mounting screw, then reattach the cover plate.

Turn on Power and Test

The final step is to turn the circuit back on and test the circuit. Be sure to test both the new and the existing outlet, using a circuit tester.

Install Drywall and Trim

Using drywall screws, reinstall the drywall piece that you earlier cut out. Take care not to drive screws into the cable running through the studs.

Reinstall the baseboard molding, using finish nails.