3-Slot vs. 4-Slot Dryer Outlets

Laundry in washing machine in kitchen
Andrew Olney/Photodisc/Getty Images

Gas clothes dryers and electric clothes dryers have much different electrical needs. A gas dryer produces heat by burning either natural gas or liquid propane (LP) gas, and it uses 120-volt electrical currently merely to spin the dryer compartment and run the controls. A gas dryer plugs into an ordinary 120-volt electrical outlet, and it has a cord with an ordinary appliance plug. An electric dryer, on the other hand, heats air with electric heating elements and runs on 220/240-volt current, which requires a much different outlet receptacle and a special heavy-duty appliance cord with a unique plug.

1:37

Watch Now: What's the Difference Between 3-Slot and 4-Slot Dryer Outlets

Electrical Dryers

Electrical dryers plug into dedicated 220/240-volt electrical outlets designed especially for dryers. There are two ways that electrical clothes dryers can be powered: with a three-prong cord plug that fits into a three-slot outlet, or a four-prong plug that fits into a four-slot outlet. 

You may have either type of dryer outlet in your home, depending on the age of your home's electrical installation. Before the year 2000, most dryer outlets were three-slot; since then, the Electrical Code has required four-slot outlets. This is a safety measure that provides a true dedicated ground pathway to the circuit in addition to the neutral pathway, which is also grounded.

Most new dryers now come with four-prong plugs, but they can be converted to use three-prong cords to fit older dryer outlets. Some dryers, though, are sold without any cord at all; you are left to buy and install whatever cord fits the dryer outlet you happen to have. 

3 and 4 slot dryer
 The Spruce

Three-Slot vs. Four-Slot Dryer Outlets

An older three-wire dryer outlet has two "hot" slots and neutral/ground slot. This is designed to fit older dryers that have cords with three-prong plugs. In newer installations, the dryer outlet has four slots, with two "hot" slots, a neutral slot, and a grounding slot. And this outlet is designed to fit newer dryers equipped with four-prong power cords. 

This difference in plug and outlet design does not mean that older dryers are not grounded, but only that they do not possess a separate, dedicated grounding pathway. In older three-slot, three-prong configurations, the neutral wire also served as the ground wire, and the dryer was grounded through the neutral connection via a jumper in the wiring compartment on the dryer. This was viewed to be sufficient, since the neutral bus in the service panel was grounded, anyway.

Eventually, however, it was recognized that the frequent presence of water in the laundry area created the potential for shock unless a separate, dedicated ground pathway was also present in the dryer. A four-slot receptacle, four-prong plug configuration is therefore somewhat safer than the older three-slot, three-prong method, since it has a dedicated grounding pathway that serves no other function.

Legally, you are allowed to continue using older three-slot dryer outlets, but you will need to convert the dryer to a three-prong cord if it doesn't have one. For example, a new dryer may come from the factory with a newer four-prong cord, which you will need to replace with a three-prong cord in order to use your older-style outlet. Similarly, if you have a four-slot dryer outlet but want to use an older three-prong dryer, it's usually a fairly easy matter to install a four-prong cord. 

Converting a Dryer Outlet or Dryer Cord Yourself

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, and 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. 

If you have very good skills as a DIY electrician, you can also consider wiring a new outlet yourself, but you need good skills and an understanding of electrical systems. For most people, it is better to have a certified electrician or appliance repairman to do this installation.