A 120-volt outlet with built-in covers for safety. The 120-volt power outlet is the standard electrical outlet in use in homes in North America. These outlets have been in use in their present form since the early 1950s. Advertisement . Video of the Day . The modern 120-volt power outlet has three holes: two parallel rectangular slots—one connected to the "live" wire and one connected to the neutral wire—and a round hole for the ground wire.
120 Volts vs. 110 Volts
Most outlets are "duplex" receptacles, with two places to plug in electrical devices. Advertisement . There are two common styles of 120-volt duplex receptacles. On "standard" receptacles, each outlet has its own round opening in the wall plate. On "decorator" receptacles, a single plastic rectangle holds both outlets. Advertisement . All modern 120-volt outlets are designed to accommodate "polarized" plugs, on which the rectangular prong for the neutral wire is slightly larger.
This is a safety measure designed to control the way an electrical device handles current. Advertisement . Any device that says it runs on 110 volts can be plugged into a 120-volt outlet. The "120 volt" label is just a nominal figure; the actual voltage could be anywhere in the range of 110-125 volts, and modern electrical devices are built to tolerate the fluctuations.
Advertisement . Some heavy appliances—such as electric clothes dryers—require 240 volts of power.
Outlets that deliver 240 volts are configured differently, so devices for 120-volt outlets can't plug in to them.
In most homes, 20-amp receptacles are fairly rare, even on 20-amp circuits. These receptacles are reserved for outlets where a heavy-duty appliance is likely to be used, such as space heaters or large motor-driven power tools. And they should NEVER be installed on a 15-amp circuit.
Tamper-resistant receptacles: The electrical code now requires that all standard outlets be fitted with tamper-resistant receptacles. This is a safety measure that prevents children from inserting objects into the slots of the receptacle and receiving a deadly shock. While old-style receptacles without tamper-resistant slots can still be purchased, you are well-advised to purchase and install newer receptacles that have the code-required safety design.
- Non-contact voltage tester
- Needle-nose pliers
- Wire strippers (as needed)
Turn off the Power
Shut off the power to the receptacle circuit by switching off the appropriate circuit breaker in your home's main service panel (breaker box). If you don't know which breaker to throw, then you'll need to shut off the main breaker, which controls power to the entire house.
Test for Power
Use a non-contact voltage tester to check for power at the outlet location: Insert the probe tip of the tester into each of the receptacle's slots. The tester should indicate no voltage.
Make sure your voltage tester has operating batteries and is functioning correctly by using it to test an outlet or switch you know is activated. Some testers light up when they sense current, others emit an audible sound, some do both.
Open the Outlet
Remove the center screw on the outlet faceplate, then remove the cover plate. Test for power again by inserting the probe of the voltage tester into the spaces alongside the body of the receptacle and touching all of the wires inside the electrical box, using the tester only (not your hands). The tester should indicate no voltage.
Examine the Wiring
Remove the mounting screws holding the receptacle strap to the electrical box, and gently extract the receptacle out of the box, gripping the receptacle by the top and bottom "ears."
Examine the wire configuration. In most cases, you will see three wire colors attached to the receptacle. Black wires are "hot" wires that carry live voltage; these should be attached to the brass-colored screw terminals on the receptacle. White wires are neutral wires and are usually attached to the silver-colored screw terminals. Bare copper wires (or sometimes green insulated wires) are ground wires; one of these should be attached to the green grounding screw on the receptacle. Another short grounding wire (known as a pigtail) may link the circuit grounding wires to a metal electrical box.
Some receptacles will have only one hot and one neutral wire attached to the receptacle, while others may have two hot wires and two white wires attached to opposite sides of the receptacle. The wiring will depend on where the receptacle is within the circuit (middle-of-run vs. end-of-run) and on how the previous electrician chose to wire the circuit. In any case, your goal is to recreate the same wiring connections on the new receptacle.
You may want to take a photo to help you remember how the receptacle is wired.
Some outlets have a switched portion and an always hot portion. Be sure to examine the outlet closely and see if the center tab has been broken out on the hot (brass screw side). See Item 8 below.
Confirm the Receptacle Amperage
Verify the proper amperage for the new receptacle.
If you find a dangerous contradiction in the wiring—for example, if a 20-amp circuit breaker is feeding wires that are only 14-gauge—it's time to call a professional, as you have a potentially dangerous situation.
If the circuit breaker, circuit wires, and receptacle all are consistent, you can proceed.
Remove the Receptacle
Disconnect the receptacle wires. Receptacles have two methods of connecting the wires: screw terminals on the sides of the receptacle, or push-in "back-wire" slots in the back of the receptacle.
Most electricians believe that the screw terminal connections are more secure, and they usually avoid making back-wire connections. If your old receptacle has back-wire connections, remove the wires by inserting a small nail or flat screwdriver into the release slot next to each wire. The wire connection should loosen and pull free of the receptacle body. If your receptacle has screw terminal connections, loosen the screws and remove the wire loops from around the screws.
If you cannot discern a color on the insulation around the wires (which is sometimes the case with old wiring), you can label them with small tabs of tape to distinguish which wires were attached to the hot screw and neutral screw.
Connect the New Receptacle
Attach the bare copper or green insulated circuit wire to the green screw terminal on the receptacle. To do this, bend a C-shaped loop at the end of the wire, loop it in a clockwise direction around the green screw terminal on the receptacle, and tighten the screw firmly.
Attach the white neutral circuit wire(s) to the silver-colored screw terminal(s) on the receptacle using the same method.
NOTE: Some receptacles are designed so the straight ends of the wires are inserted into slots next to the screw terminals on the side of the receptacle. Do not connect more than one wire to a single terminal.
If the old receptacle was back-wired, don't use the back-wire fittings on the new receptacle unless they are the type that can be tightened with a screw. Instead, trim off the bare end of each wire, then strip about 3/4 inch of insulation from the wire, using wire strippers. Bend the wire into a C-shaped loop to connect to the side screw terminal.
Complete the wire connections by attaching the black (hot) wires to the brass-colored screw terminals, using the same technique. Do not connect more than one wire to a single terminal.
Mount the Receptacle and Turn on the Power
Tuck the wires neatly into the box as you push the receptacle into place against the box tabs. Secure the receptacle to the box with the two receptacle screws. Install the faceplate onto the new receptacle.
Restore power to the circuit by switching on the circuit breaker, then test the receptacle for proper operation.
The vast majority of outlets will be standard appliance outlets that are replaced using the method described above. But you may run into two variations that call for slight differences in the technique used for replacing them.
Although not common, your outlet receptacle may be wired so it is "split." In this scenario, the top and bottom halves of the receptacle operate independently. Sometimes this is done so that different circuits can feed the top and bottom halves of the receptacle; for example, when the outlet is wired so that a wall switch controls one half of the receptacle. In this case, one-half of the receptacle operates normally, but the other half is activated only when the wall switch is on.
In split receptacles, a brass connecting tab along the side of the receptacle is broken off, so there is no electrical pathway between the two halves. As you are replacing a receptacle, carefully inspect these tabs. If they have been severed in the old receptacle, then make sure you break off the tab on the new receptacle before installing it. All other steps for replacing such a receptacle are the same as for a standard receptacle.
Replacing a GFCI receptacle is not difficult if you've paid attention to how the wires were connected to the old receptacle. It's important to know that a middle-of-the-run GFCI receptacle has two pairs of hot and neutral wires and that each pair must be connected to specific screw terminals. The wires entering the box from the power source must be connected to the hot and neutral screw terminals marked "LINE," while the pair of wires running onward to other receptacles or fixtures must be connected to the corresponding screw terminals marked "LOAD".
When replacing a GFCI receptacle, carefully review the manufacturer's wiring schematic to make sure you connect it correctly. But other than making sure the incoming and outgoing wires are connected to the proper screw terminals, the replacement process is the same as for standard receptacles.
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