Installing a plug-in receptacle for an electrical outlet can be a very easy job when it involves the simple replacement of an existing receptacle, but it can be a bit more difficult if it involves running a new circuit from the main service panel or extending an existing circuit. The following project shows how to connect the receptacle when the electrical box has already been installed and when the necessary NM electrical cables have been run in the wall cavities.
Carefully read the following instructions to determine if your skills and understanding are sufficient to do the job.
How to Wire and Install an Outlet
When to Call in a Professional
Homeowners without experience with home wiring projects and repairs may want to have an electrician run cables to the new outlet location and complete any service panel connections if the outlet involves a new circuit or extension of an old circuit. This work is certainly possible for a homeowner to do, but any work that involves the main service panel is inherently dangerous and should not be attempted if you don't have experience with this kind of work.
However, replacing an old receptacle with a new one, or installing receptacles when the circuit wiring and electrical boxes are already in place, as described here, is a job that most homeowners can do safely.
Circuit Wiring for Receptacles
Household outlet receptacles can be wired in one of two ways, depending on where the outlet falls along the circuit. When an outlet falls in the middle of the circuit run, there will be two cables (or occasionally three) entering the electrical box. One cable is bringing power into the box from the power source, while the other cable (or cables) are carrying power onward to other outlets or fixtures.
This kind of middle-of-run configuration can be wired so that the power supply cable is connected directly to one set of brass (hot) and neutral (silver) screw terminals on the receptacle. The outgoing cable can then be connected to the other set of screw terminals so that all power flows through receptacle as it continues to the rest of the circuit. But a better method of wiring, followed by most electricians, is to use pigtail wires attached to one set of hot and neutral screw terminals to connect to the ingoing and outgoing cables. The advantage of this method is that the power flow will continue through the circuit even if there is a problem with individual receptacles.
Wiring a receptacle becomes very easy when it falls at the end of the circuit run. In this case, there is only one cable in the box, and the hot and neutral wires are simply secured to one pair of brass and screw terminals on the receptacle.
All electrical work comes with inherent risks, so make sure to carefully follow basic wring practices:
- Before touching any wires in an electrical box, always test for power with a non-contact voltage tester to make sure the power is off. Before conducting the test, make sure your tester is working properly by first testing it on an outlet that you know is hot (energized); the tester should light up, indicating it is working.
- The wire connections must be made carefully to ensure safety and proper operation. A wire coming loose from an outlet can create a serious fire or shock hazard. The safest way to connect wires is to use the outlet's side screw terminals, a procedure known as side wiring. Another common method, called back wiring, uses self-clamping rear terminals. This method is usually avoided by professionals since such connections are notorious for coming loose.
- Never connect more than one wire to a single terminal. If there is more than one cable in the electrical box, use pigtails to connect the receptacle to the circuit wires. A pigtail is a short length of wire that you install between the outlet terminal (or ground screw) and a group of circuit wires. Pigtail wires are easily created by cutting short lengths of scrap NM wire and stripping the ends. Grounding pigtails made with green insulated wires are also sold at home centers and hardware stores.
- Metal electrical boxes must be connected to the ground system via a grounding pigtail that connects to the circuit ground wires and the receptacle. One end of this pigtail is connected to a green grounding screw on the metal box, and the other end is joined to the circuit grounding wires and to the receptacle's grounding pigtail. Plastic electrical boxes do not require grounding.
- Receptacle, NM cable, and circuit breaker must all match for amperage ratings. Most household outlet circuits are either 15-amp or 20-amp 120-volt circuits. A circuit controlled by a 15-amp circuit breaker calls for 14-gauge NM cable and a receptacle rated for 15 amps. A circuit powered by a 20-amp circuit breaker calls for 20-amp receptacles, and it is wired with 12-gauge NM cable. Make sure to buy a receptacle that is rated at the correct amperage. A 20-amp receptacle is identified by the T-shaped slot found in one of the vertical slots.
- The Electrical Code in most jurisdictions now requires tamper-resistant (TR) outlets for new installations. Identified by a "TR" imprint, these outlets have internal wings or shutters behind the slots, which don't open unless you insert two prongs from a plug at the same time. This helps prevent children from getting shocked by inserting a knife, pin, or paper clip into the outlet slots.
- Most electrical codes require that the edge of the receptacle box can be recessed no more than 1/4 inch from the finished wall surface. If the box is embedded too deeply, you can install a box extender ring to bring the box up to code.
Equipment / Tools
- Non-contact voltage tester
- Cable ripper
- Cutting pliers or utility knife
- Wire strippers
- Wire connectors
- Needle-nose pliers
- Scrap NM cable (as needed)
- Outlet receptacle with cover plate
Turn Off the Power and Test for Power
Locate your home's main service panel. Also known as the breaker box or fuse box, the main service panel is usually located in a utility area, such as a basement, kitchen pantry, garage, hallway, closet, or on an outside wall.
Turn off the power to the circuit powering the new outlet by switching off the circuit breaker. Test the outlet for power using a non-contact voltage tester to verify that the power is off.
If you are replacing an existing outlet, remove the old outlet at this time.
Prepare the Cables
Electrical cables feed through holes in the back or sides of the outlet's electrical box. They are secured in place by metal cable clamps or by pressure-fit clamps mounted in the box. Generally, the outer sheathing of the NM cable should just barely extend into the box, with 6 or 7 inches of each conducting wire extending into the box. Cable wires longer than this are unwieldy and difficult to stuff into the box, so if they are longer than this, you may want to trim them down with wire cutters.
If necessary, remove the outer sheathing on the NM cable by slitting the jacket with a cable ripper, then trimming away the sheathing and paper insulation with a utility knife or wire cutters. Then, cut off the ends of the individual conducting wires so that no more than 6 to 7 inches extends past the front of the box.
- Note: If you're replacing an old outlet receptacle, you probably will not need to prepare the cables or strip the individual wires.
Strip the Wires
If necessary, strip away 1/2 to 3/4 inch of plastic insulation from the end of each insulated wire in the box, using wire strippers. If you are replacing an old outlet receptacle, make sure that the ends of the wires are in good condition and have no nicks or scorch marks; if they do, trim off the damaged portion then strip away insulation from the end of the wire.
- Note: Follow the manufacturer's recommendations when using wire connectors to make connections, such as when pigtailing. Some twist-on wire connectors require stripping only about 1/2 inch of insulation. Stripping too much insulation can leave bare wire exposed under the wire connector's cap. Many outlet receptacles have a stripping gauge imprinted on the back of the device to tell you how far the wires should be stripped. For screw terminal connections, this is usually about 3/4 inch.
Attach Pigtail Wires to the Circuit Wires
Install pigtail wires if there is more than one cable in the box. Using a scrap of the same type of circuit cable, cut 6-inch lengths of each type of wire in the cable. Strip one end of each pigtail at 1/2 inch and the other end at 3/4 inch. The 1/2-inch end will be connected to the circuit wires with a wire connector, while the 3/4-inch end will be bent into a hook shape and connected to a screw terminal on the receptacle.
Join the bare copper (or green insulated) pigtail to the ground wires in the circuit cables, using a wire connector, following the manufacturer's directions. Do the same with the white (neutral) pigtail, then the black (hot) pigtail, so you have one ground, one white, and one black pigtail connected to the circuit wires.
- Note: If the electrical box is metal, install an additional grounding pigtail and connect it to the ground screw on the box.
Connect the Ground Wire to the Receptacle
Form a J-shaped hook on the end of each wire (or pigtail), using needle-nose pliers. Fit the hooked end of the ground wire around the ground screw on the new receptacle. The wire should hook around the screw in a clockwise fashion. This way, the screw will close the hook as you tighten the screw.
Use needle-nose pliers to squeeze the hook closed around the threaded shank of the screw. Tighten the ground screw with a screwdriver. The hook should fit snugly around the shank of the screw.
Attach the Neutral and Hot Wires to the Receptacle
Connect the white neutral wire or white pigtail to one of the silver (neutral) screw terminals on the receptacle, hooking the wire around the screw terminal in a clockwise direction. The insulation should just touch the screw terminal. Connect the black hot wire or black pigtail to one of the brass (hot) screw terminals on the receptacle.
For standard outlet wiring, the white neutral wire can go on either of the two silver terminals, since they are interchangeable. Likewise, the black hot wire can go on either brass screw terminal.
Attach the Receptacle to the Box
Confirm that all wiring connections are secure by gently tugging on each wire. Reconnect and retighten any loose wires. Carefully tuck the wires into the box; it often helps to bend them in one or two places, but do not create sharp bends. Press the receptacle's mounting strap against the box, then secure it by threading the mounting screws into the top and bottom of the box.
The receptacle can be oriented with the ground slot (the D-shaped hole) facing up or down. Technically, it is considered safer to have the ground slot on top. With this orientation, if a cord plug is partially pulled out of the outlet to expose the plug's prongs, an object falling onto the plug is blocked by the grounding prong before it can short-circuit across the hot and neutral prongs.
Attach the Cover Plate
Fit the cover plate over the outlet and secure it with the mounting screw. Restore power to the circuit by switching on the circuit breaker. Plug in an electrical device to the outlet to make sure the receptacle is working properly. You can also use an inexpensive plug-in receptacle tester to confirm that the receptacle has power, is wired correctly, and is properly grounded.