Prior to 1996, electric dryers were supplied by a dedicated circuit that had three conductors: two hots and a neutral. There was no ground slot on the receptacle (outlet), and dryer cords had no ground wire or ground prong. The ground for the appliance itself was connected to the neutral wires. This system worked pretty well and is still in use in many homes today. In 1996, the National Electrical Code (NEC) began requiring 4-conductor outlets with a separate ground. To be code-compliant, all newly installed outlets for dryers must be compatible with 4-prong, grounded dryer cords.
4-Prong Dryer Receptacle Wiring
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, while the 240-volt service supplies the heating elements. The NEC requires that dryers have a dedicated circuit with a minimum of 30 amps. This calls for a 30-amp, double-pole breaker and 10 AWG wire.
In a standard installation with nonmetallic (NM) cable, 10-3 NM-B (with ground) cable is run from the service panel to a recessed outlet. If the outlet is surface-mounted, such as on a concrete or block wall, the circuit includes cable or insulated (THHN/THWN) wires inside nonmetallic or EMT conduit. The outlet may be a special surface-mount receptacle or may be a standard dryer receptacle installed in a surface-mounted box.
Connecting the 4-Conductor Outlet
Once the circuit cable is run and the receptacle box (as applicable) is installed, connecting a 4-prong outlet follows standard wiring procedure.
- Connect the black hot wire to one of the two brass hot terminals on the outlet. The hot terminals are interchangeable.
- Connect the red hot wire to the other brass terminal on the outlet.
- Connect the white neutral wire to the silver neutral terminal on the outlet.
- Connect the ground wire to the ground screw on the outlet. Note: 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 connect the other to the ground screw on the box.
- Mount the outlet to its box, and install the cover plate.
Wiring the Circuit Breaker
Warning: If you are not experienced with working inside an electrical service panel, hire an electrician to install the circuit breaker. Even if you install the circuit cable, box, and outlet, you can 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.
The 30-amp breaker is wired with standard double-pole configuration.
- Turn off the main circuit breaker in the service panel.
- Remove the panel cover (dead front cover) to expose the panel wiring.
- Test the branch circuits with a voltage tester to confirm the power is off. The incoming power from the utility service lines will remain live.
- Connect the ground wire from the outlet's circuit cable to the panel's ground bus bar.
- Connect the white neutral circuit wire to the panel's neutral bus bar.
- Connect the red and black hot circuit wires to the two brass terminals on the 30-amp, double-pole (120/240-volt) circuit breaker.
- Install the breaker into the panel so it snaps securely onto both hot bus bars.
- Reinstall the panel cover.
- Turn off all of the branch circuit breakers in the panel.
- Turn on the main breaker, then switch on each of the branch circuits, one at a time.
Find a Good Location
Position the 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.
Measure a Decent 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 often keeps the plug accessible while hiding it from view behind the dryer, depending on the height of the dryer.
Orient the Outlet Properly
Orient the outlet so the L-shaped (neutral) slot is at the bottom. This ensures the cord will extend downward from the outlet.