What’s the Difference Between 3 Prong vs 4 Prong Dryer Outlets?

Electric dryers use so much energy that they run on 240V current: twice the amount of a regular wall outlet. Newer homes have 240V outlets that accept four-prong plugs.

Older homes tend to have 240V outlets that only accept three-prong plugs. What’s the difference and can you convert from one to the other?

• Three-prong plugs and outlets: Outlets with three slots have one ground slot and two live slots. They do not have a separate neutral slot; the ground is intended to act as both a neutral and a ground. This is an older configuration that was changed in 1996 for safety.
• Four-prong plugs and outlets: Outlets with four slots have one ground slot, two live slots, and one neutral slot. The risk of shock is minimized because the separate neutral slot (wire) returns non-consumed power.

What Is a Three-Slot Dryer Outlet?

Before 1996, 240V clothes dryers had three-prong cords that plugged into three-prong 240V outlets.

• 120V hot slot
• 120V hot slot
• Combined ground/neutral slot

The ground was bonded to the neutral connection. One wire served both functions—as the neutral current pathway and as the grounding pathway. In rare circumstances, there is a very small chance of shock with this configuration.

Since 1996, the NEC and standard local code practice have mandated that new installations include four-slot dryer outlets for 240V dryers and that dryers must be fitted with four-prong cords to match them.

What Is a Four-Slot Dryer Outlet?

Since the 1990s, the electrical code has directed that 240V dryer outlets should have a four-slot configuration:

• 120V hot slot
• 120V hot slot
• Neutral slot
• Ground slot

A four-slot receptacle, four-prong plug configuration is somewhat safer than the older three-slot, three-prong method since it has a dedicated grounding pathway that does only one thing: provide grounding.

When to Choose a Four-Slot Outlet or Three-Slot Outlet

• New installations: If installing a new outlet for a 240V dryer, do not install a three-slot dryer outlet. The electrical code no longer allows this. Always install the proper four-slot outlet.
• Older dryers: If you have an older dryer with a three-prong cord, replace it with a four-prong cord to match your new four-slot outlet. This is an easy project that takes just a few minutes to complete.

Converting a Dryer Cord vs. Converting a Dryer Outlet

• Converting the dryer cord: Changing a dryer cord from a three-prong to a four-prong (or vice versa) is an easy project for most people. The process is relatively simple. This is usually the best way to deal with the situation when your dryer cord doesn’t match the dryer outlet present in your home. It’s easier and safer than converting the dryer outlet.
• Converting a dryer outlet: If you are very skilled as a DIY electrician, you can consider wiring a new outlet yourself, but this requires a thorough understanding of electrical systems. For most people, it is better to have a certified electrician or appliance repair professional do this installation. 

Gas vs. Electric Dryers

A dryer plug will fit into either a three-slot or four-slot dryer outlet but it’s not always so straightforward. This also only applies to electric clothes dryers but not gas models. Gas clothes dryers and electric clothes dryers have different electrical needs:

• Gas: A gas dryer produces heat by burning either natural gas or liquid propane (LP) gas, and it uses a 120V electrical current merely to spin the dryer compartment and run the controls. It plugs into a 120V electrical outlet with a cord fitted with an ordinary appliance plug.
• Electric: An electric dryer heats the air with electric heating elements and runs on a 240V current. This requires a different outlet receptacle and a special heavy-duty appliance cord with a three-prong or four-prong plug to fit into a corresponding three-slot or four-slot outlet. When buying a new electric dryer, you can choose and install a cord that matches the outlet in your home.