When moving a newer electric dryer into an older house, it's not uncommon to find that the cord and plug included with the new dryer doesn't fit the 240-volt dryer outlet. Before the mid-1990s, most electric clothes dryers operated with three-prong plugs that fit into three-slot outlets, but since 1996, the electric code has required four-slot outlets. The mismatch can work both ways: You may find that a newer dryer doesn't fit an older-style outlet, or that an older clothes dryer doesn't fit a newer outlet.
Three-Slot vs. Four-Slot Outlets
The change in electric dryer plugs and outlets was made for enhanced safety. In a traditional three-slot 240-volt outlet, there are two hot slots and one neutral slot. These correspond to the two hot and one neutral wire in the three-prong cord. On the dryer, the metal case of the appliance has a ground screw, and this is connected to the neutral wiring terminal of the dryer. In the event of a short to ground, the electrical current is intended to travel on the neutral wire back to the breaker box.
A four-slot outlet has a fourth slot that is dedicated as an equipment grounding conductor. The four-prong cord has a dedicated ground wire that connects to the metal dryer case. The ground and neutral pathways are separate, reducing the change of accidental shock.
Watch Now: How to Change a 4-Prong Dryer Cord to Fit a 3-Slot Outlet
Two Possible Solutions
If you are faced with the problem of a dryer plug and dryer outlet that don't match, there are two possible remedies. One is to replace the old circuit by installing new four-wire cable and a four-slot outlet, each with a dedicated ground. This is a job for an electrician, and it brings the circuit up to code. The other option is to replace the four-prong cord with a three-prong cord. This is an allowable remedy under the electrical code, which "grandfathers in" older installations. It is only new installations where the four-slot dryer receptacles are required; existing three-slot receptacles are allowed to remain.
Simply replacing the dryer cord is by far the easier solution and the one that most DIYers pursue when they are faced with the problem. However, this configuration is not as safe as a four-wire circuit.
While you will be working on the dryer while it is unplugged, it is best to be cautious and shut off the circuit powering the dryer before you unplug it or plug it back in.
Equipment / Tools
- Voltage tester
- Magnetic nut driver
- UL-listed three-prong dryer cord with strain-relief clamp
Shut off the Power
In the main service panel (breaker box), find the double-pole circuit breaker that controls the clothes dryer and flip the breaker to the OFF position. At the dryer outlet, check for power using a non-contact voltage tester.
Unplug the dryer and move it to a location where you have access to the back panel. You may need to disconnect the dryer vent to move and work on the dryer. Make sure you have plenty of light while working.
Most dryer circuits have 30-amp breakers, indicated by a "30" stamped on the switch bar of the breaker. A double-pole breaker is twice as wide as a standard (single-pole) breaker, and most service panels have only a few double-pole breakers.
Remove the Dryer's Electrical Connection Cover
Use a screwdriver to remove the cover on the electrical connection box on the back of the dryer. It is located just above where the power cord comes out of the dryer and is attached with one or two screws. Set the cover and screws aside.
Detach the Electrical Cord
Remove the strain-relief clamp holding the cord by removing the two screws joining the two halves of the clamp together. Separate the two halves of the fitting and pull them out of the hole individually.
Using a magnetic nut driver or screwdriver, disconnect the black and red cord wires from the left-side and right-side terminals on the dryer's terminal block. These are the hot wire connections. Disconnect the white wire from the center terminal. Disconnect the green grounding wire from the machine case by unscrewing the green grounding screw.
Slide the four-prong cord out of the connection box.
Jumper the Neutral to the Ground
Remember, a three-prong cord configuration requires that you connect the dryer's neutral terminal to the case ground.
Locate the white machine wire that is connected to the neutral (center) screw terminal. Disconnect it and reconnect it under the green grounding screw. Tighten the screw firmly.
Alternatively, the dryer may have a metal bonding strap (typically connected under the ground screw) instead of a white machine wire. If so, attach the strap to both the ground screw and the neutral (center) terminal.
Connect the Three-Prong Cord
Thread the loose end of the three-prong cord through the hole in the electrical connection box. Connect the outer two wires (the hot wires) on the cord to the outer two screws terminals, one on each screw. Connect the center wire to the center (neutral) terminal. If there a bonding strap for the ground, it must be connected to the neutral terminal along with the center cord wire.
Tighten all wire connections firmly.
Install the New Strain-Relief
Slide one half of the strain-relief clamp into the hole under the cord wire. Fit the other half of the clamp in the same way but on the top of the cord. Squeeze the two halves together with pliers and thread the screws into the holes. Tighten the screws until the cord is secure.
Do not re-use the original strain-relief clamp with the new three-prong cord. Clamps for four-prong cords are round and will not properly fit the flat shape of a three-prong cord. Use the strain-relief that comes with the new cord, or buy a compatible clamp separately.
Plug in the Dryer
Reattach the connection box cover plate with its screw(s). Slide the dryer into place, and reconnect the dryer vent duct, if necessary. Plug the cord into the outlet. At the main service panel, turn the dryer's circuit breaker back to the ON position, then test the dryer for proper operation.
Installing a Four-Prong Cord to Fit a Four-Slot Outlet
If you have the related but opposite situation—an older dryer with a three-prong cord but a newer house with a four-slot outlet—it is equally easy to replace an old cord with a new four-prong cord that will fit a four-slot outlet. Most of the steps described above will be the same, with one important difference: The neutral terminal and ground screw will not have a jumper between them, and each will be connected to its own cord wire.