How to Wire a 4-Prong Receptacle for a Dryer
Before 1996, electric dryers were supplied by a dedicated circuit that had three conductors: two hot wires and a third that was used as both a ground wire and a neutral wire. There was no dedicated ground slot on the receptacle (outlet), and dryer cords had no ground wire or ground prong. This system worked pretty well (and is still in use in many homes today), but there's more potential for an electrical shock since the ground and neutral wires are combined.
In 1996, the National Electrical Code (NEC) requirements changed to include 4-conductor outlets with a separate ground that eliminates the possibility of a current traveling back to the machine, causing shock or even fire. To be code-compliant, all newly installed outlets for dryers must be compatible with 4-prong, grounded dryer cords.
Wiring for a 4-Prong Dryer Receptacle
A 4-prong dryer outlet is wired as a 120/240-volt circuit. The 120-volt service is for the dryer's timers, sensors, and other electronics (and if your dryer has a light inside, this too is 120 volts), while the 240-volt service supplies power to the heating elements and the drum motor. The NEC requires that dryers have a dedicated circuit with a minimum of 30 amps. This calls for a 30-amp, double-pole breaker wired with 10 AWG wire.
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What You'll Need
Equipment / Tools
- Wire strippers
- Needle-nose pliers
- Voltage tester
- 4-slot dryer outlet
- 4x4-inch electrical box
- 30-amp double-pole breaker (must be compatible with your service panel)
- 10-3 NM-B cable (with ground) or EMT conduit and 10-gauge greenfield wire
Install a Receptacle Box and Run the Cable
In a standard installation with nonmetallic (NM) cable, 10-3 NM-B (with ground) cable is run from the main service panel to a recessed outlet box. If the outlet is surface-mounted (like on a concrete or block wall), the circuit is usually run with insulated (THHN/THWN) wires inside nonmetallic or EMT conduit. The outlet may be a special surface-mount receptacle or a standard dryer receptacle installed in a surface-mounted box.
How you connect the cable or wires into the box will depend on the installation. With NM cable in finished walls, the cable is threaded into the box and secured with a cable clamp. In surface-mounted conduit installations, the conduit is secured to the box with a collar and individual conducting wires are snaked through the conduit and into the box.
Make the Ground Wire Connection at the Outlet
Connect the bare copper (or green insulated) ground wire to the ground screw on the outlet.
If the outlet is mounted in a metal electrical box, join the circuit ground wire to two grounding pigtails; connect one pigtail to the outlet's ground screw and the other to the ground screw on the box.
Connect the White Neutral Wire at the Outlet
Strip away about 3/4-inch of insulation from the white wire in the cable. Connect the white neutral wire to the silver-colored (neutral) terminal on the outlet. Usually, the connection involves inserting the bare wire into the neutral slot, then securing it by tightening a screw. In some styles, you may need to loop the wire around a screw terminal before screwing it down.
Connect the Two Hot Wires
Next, strip about 3/4-inch of insulation from the red and black hot wires. Secure them to the two hot terminals on the outlet.
Secure the Outlet
Insert the outlet into the box, carefully tucking the wires in place, then secure it using the mounting screws. Install the outlet cover plate.
Prepare to Install the Circuit Breaker
Turn off the main circuit breaker in the service panel. Remove the panel cover to expose the panel wiring. Locate two adjacent empty slots in the service panel where the double-pole breaker will fit. Remove the slot tabs on the panel cover where this breaker will be located.
Open a knock-out in the side wall of the service panel, then insert the cable through the opening and secure it with a cable clamp. As you are threading the cable into the panel, be careful not to allow the wires to brush against the bus bars.
You will need plenty of excess wire; strip away at least 18 inches of the outer jacket from the cable. Strip about 3/4-inch of insulation from the ends of the white, black, and red wires.
If you are not experienced with working inside an electrical service panel, this is the point where you should hire an electrician to install the circuit breaker. Even if you've installed the circuit cable, box, and outlet yourself, you can still have an electrician make the final connections at the service panel.
Service panels pose a deadly risk of shock because the utility service cables feeding the panel—and the terminal lugs they connect to inside the panel—remain live at all times. Shutting off the main circuit breaker does not turn off the power to the service feed.
Now, test the branch circuits inside the panel with a voltage tester to confirm the power is off. This is done by touching one probe of the tester to a screw terminal on the breaker while touching the other probe to the ground bus bar. Remember that the incoming power from the utility service lines will remain live; do not touch either of the hot bus bars running down the back of the panel.
Connect the Ground Wire
Connect the ground wire from the dryer outlet's circuit cable to the panel's ground bus bar. This involves inserting the bare end of the wire into a slot in the ground bus bar and tightening the set screw to secure the wire. Carefully fold the excess wire and arrange it along the outer edge of the panel.
Connect the Neutral Wire
Connect the white neutral circuit wire by inserting the bare copper end of the wire into a slot in the panel's neutral bus bar, then tightening the set screw. Carefully fold the excess wire and tuck it along the edge of the service panel.
Note: In almost every case the ground bus bar and the neutral bus bar are the same, but this is not the case if the panel you are connecting to is a "sub-panel," which has a separate ground bus bar from the neutral bus bar.
Connect the Hot Wires to the Circuit Breaker
Connect the red and black hot circuit wires to the two screw terminals on the 30-amp, double-pole circuit breaker. For most breakers, this involves simply inserting the bare ends of the wires into the slots on the breaker and tightening the set screws. Carefully fold the excess wire and tuck it along the edge of the service panel.
Mount the Circuit Breaker
Line up your new breaker so the clips slide over the mounting hooks adjacent to the hot bus bar. Press the breaker down firmly until it snaps into place. Depending on the brand of your service panel, inserting the breaker can be either a pivoting action or a firm inward push to snap the breaker onto the bus bars.
Finish the Installation
Reinstall the panel cover. Turn off all the branch circuit breakers in the panel. Turn on the main breaker, then switch on each of the branch circuits, one at a time. This process prevents the sudden power surge that occurs if the main breaker is turned on while all the circuit breakers are activated.
Test the Outlet
Use a voltage tester to verify that the dryer outlet is carrying power.
Install the Appliance Cord
You are now ready to install the 4-prong appliance cord on your dryer and plug it into your revamped dryer outlet.
When to Call a Professional
This project requires a good knowledge of—and experience working with—electrical circuits. It involves making circuit connections at the main service panel and should not be attempted unless you are fully confident in your abilities. If you are not certain, it is best to have this work done by a professional electrician.
Tips for Installing a Dryer Outlet
- Find a good location: Position the dryer outlet box in a convenient location for both the dryer cord and the dryer vent. Whenever possible, dryers should be near an exterior wall to minimize the length of the vent run.
- Position the outlet at a convenient height: Local codes typically do not specify an installation height for dryer outlets, but it's helpful to be able to reach the plug without moving the dryer all the way out from the wall. A height of about 30 to 36 inches from the floor usually suffices to keeps the plug accessible while hiding it from view behind the dryer.
- Orient the outlet properly: Orient the outlet so the L-shaped (neutral) slot is at the bottom. This ensures the dryer cord will extend downward from the outlet.
Electrical Safety: Safety and Health for Electrical Trades. United States Department of Health and Human Services.
National electrical code changes for 1996 and USA participation in International Energy Agency activities related to photovoltaics safety and grid interconnection. Sandia National Laboratories with the United States Department of Energy.
NEC 2017. National Fire Protection Association.
Home Wiring Hazards. Consumer Products Safety Commission.
2017 NEC Edition Chapter 60 Building Code Standards Part 6 Electrical Installations. Montana Department of Labor and Industry.