Due to changes in the National Electrical Code (NEC), recommended wiring for electric clothes dryer outlets changed in 1996. Before the change, dryer outlets were 3-slot devices that accepted 3-prong cords. This configuration did not include a dedicated ground connection; the dryer's equipment ground (case ground) was connected to the neutral conductor in the dryer cord and the household circuit.
Since the code change, new dryer outlets must be wired with separate neutral and ground wires. These outlets have four slots and will accept only 4-prong electrical cords. Homeowners owning older dryers with 3-prong cords are sometimes perplexed when they move into a home that has a newer 4-slot outlet. In this instance, the solution is to replace the old 3-prong cord with a 4-prong cord to match the new outlet. Fortunately, it is a very easy project.
However, be aware that it's still legal to use 3-slot outlets—the code has no requirement that they must be replaced with 4-slot outlets. This is why new clothes dryers are generally sold without any power cord at all, so that you can install whatever cord style matches your outlet.
What Is the Difference in Wiring?
The key difference in the wiring configuration between 3-prong and 4-prong cords is that, with the older setup, the 3-prong cord has only two hot wires and one neutral wire—there is no separate ground wire. Therefore, the dryer's neutral wire was tied to the ground connection on the metal case of the dryer. Such a configuration creates a chance of shock in the rare case that the ground wire opened up. The bare wire would be energized, trying to return current to the source. The old 3-prong configuration would trip the breaker in the case of a short circuit, but in the broken ground condition, the entire bare ground and metal case would be energized. This was the reason the code changed to require the 4-wire configuration.
A 4-prong cord, by contrast, has a separate ground wire, which means that the dryer's neutral and ground are not connected together, thereby minimizing the chances that the appliance's metal case will become energized during an open neutral condition. When you convert from the 3-prong to the 4-prong configuration, you must make sure that the dryer's neutral terminal is not connected to the case ground.
Because you are not working on household circuit wires while installing the cord, this is a very safe project. But it is crucial that the wire connections you make when attaching the cord to the appliance are correct and very secure. Loose connections can lead to short circuits and sparking once the appliance is plugged in for use.
- Give a good tug on each wire as you complete the connection to make sure it is secure.
- Always attach the strain-relief fitting. This will relieve pressure on the wire connections that can occur when the appliance is moved around.
Never plug in a dryer cord unless it's fully connected to the dryer. Plugging in a cord sends 240 volts of electricity to the bare wire ends of the cord. If the ends touch together or touch you, they'll create a potentially lethal short circuit.
Replacing a 3-Prong Electrical Dryer Cord With a 4-Prong Cord
Equipment / Tools
- Phillips screwdriver
- Nut driver or socket wrench (as needed)
- Adjustable pliers (optional)
- UL-listed, 30-amp, 4-prong dryer cord
- Strain-relief fitting for 4-prong cord
Remove Coverplate for Electrical Connections
Make sure the dryer is unplugged from the electrical source, then remove the metal plate covering the cord's wiring connections on the back of the dryer. It should be directly above the place where the cord comes out.
Remove the Strain-Relief Fitting
Remove the screws on the strain-relief fitting that secures the cord to the back panel of the dryer. Separate the two halves of the fitting and pull them out of the hole one at a time.
Disconnect the Old Cord
Disconnect the old 3-prong cord by removing the three screws (or nuts with studs, as used in some cases) securing the wire ends to the dryer's terminal block. The two outer terminals are the hot terminals, and the center terminal is the neutral.
Pull the cord out through the hole to remove it from the dryer.
Separate the Dryer's Neutral From the Ground
Disconnect the dryer's neutral wire from the ground screw to convert the wiring configuration from 3-prong to 4-prong. You may have one of two different configurations:
- If there is a white wire coming from inside the dryer and connecting to the ground screw, remove it from the ground screw and connect it to the neutral (center) terminal on the dryer's wiring block.
- If there is a short white wire or metal strap connected to the neutral terminal on the wiring block and the ground screw, remove the wire or strap from the ground screw.
Connect the New 4-Prong Cord
Install the new 4-prong cord by inserting the loose wire end through the hole in the dryer's back panel and making the following connections:
- Connect the green cord wire to the ground screw.
- Connect the white cord wire to the center neutral terminal. If your dryer has a pre-attached white wire, both wires will now be connected the neutral terminal.
- Connect the black cord wire to either the left or right terminal.
- Connect the red cord wire to the other hot terminal. The hot terminals are interchangeable; each can connect to the black or the red wire, but only one wire goes on each terminal.
Tighten each terminal screw firmly, and double-check them to make sure they are tight.
Attach the Strain-Relief Fitting to the New Cord
To install a new strain relief fitting, first slip the tab of the top half of the fitting and position the saddle (semi-circle) of the fitting over the top of the cord. Do the same with the bottom half of the fitting below the cord.
Squeeze the two halves together (sometimes it helps to use pliers to gently squeeze them together), and secure the halves with the fitting screws. Snug the screws so the cord is held firmly but is not deformed by the pressure.
Reinstall the Dryer's Electrical Cover Plate
Reinstall the cover plate with its screws. To test the dryer for proper operation, check the dryer's control knob(s) to confirm that everything is in the off position, then plug the dryer into a 4-prong dryer outlet. Run the dryer for a few minutes to make sure everything works. Be sure to connect the dryer vent duct if you removed it (or if it's a new installation) before using the dryer.