The Difference Between 2- and 3-Prong Electrical Plugs (and Why It Matters)

Unless you live in an older home with two-prong outlets, you probably don't put much thought into plugging and unplugging electronic devices and appliances.

But at some point, you've likely noticed that some plugs have two prongs, while others have three, and may have even wondered why that is, and what the difference is between them. Maybe not. Either way, here's what to know.

Two-prong outlets vs. three-prong outlets

Before getting into plugs, let's start with the outlets. Two-prong outlets were introduced in 1962, but not everyone made the switch right away: It's not unusual to find them in some homes built throughout the rest of the 1960s and even into 1970s and 1971.

After that, three-prong outlets became the norm, and remain so to this day--although, as you can see in the graphic below, they've gotten increasingly advanced over the years, offering additional safety protections.

Now, let's talk holes. Both two- and three-prong outlets have two parallel vertical openings:

Three-prong outlets also have a third opening below the slots (i.e. the "ground"), which connects to the ground wire.

We'll turn it over to the professionals at Shockley Electric to explain what happens next:

When you plug a device with two prongs into an outlet, power flows from your home's electrical panel through the hot prong, to your device (powering it in the process), and back to the neutral prong, which sends the electricity back to the breaker box and completes the circuit.

At least that's how things are supposed to work.

Why three prongs are safer than two

Let's say there's an unexpected burst of electrical current (more than the 120 volts most outlets are designed to handle), or a loose wire inside an appliance comes in contact with its metal case.

The current has to go somewhere, so it travels through the appliance--possibly damaging or destroying its electrical components along the way--and into your body, resulting in a potentially serious shock. The current could also make its way into the structure itself and cause a fire.

But that wouldn't happen with a three-prong outlet, because the excess electrical current would be sent back to the main electrical panel (which should be grounded), rather than the user or the house. Or, if it's a three-prong ground fault circuit interrupter outlet (GFCI)--the kind with the buttons, found in bathrooms--the breaker would detect it, and immediately stop the flow of electricity to the outlet.

Why don't all new appliances and electronic devices have three-prong plugs?

Given that three-prong plugs are considered safer, you may be wondering why, 60 years after the introduction of three-prong outlets, some new appliances have two-prong plugs.

In short, two-prong plugs are cheaper to make, so manufacturers will use them whenever they're able to do so and still meet the standards of independent safety testing organizations like Underwriters Laboratories (UL).

Since 1969, three-prong plugs have been required for major appliances, but two-prong plugs are still used on "double insulated" appliances, which have two levels of insulating materials between their electrical components and the external surfaces people touch. This provides protection against fire and getting shocked, even without the grounding prong.

Can I use an adapter to plug three-prong plugs into two-prong outlets?

Technically yes, this works, but it's not considered safe. Commonly referred to as "cheater plugs," "cheaters," or "pigtail adapters" they may be a convenient workaround, but when used in an outlet without a dedicated grounding connection, these adapters offer no protection against fire, electrical shocks, or damage to the device that's plugged in.

And this should go without saying, but don't cut the third prong off of a plug so it can fit into a two-prong outlet. Again, even if it does allow you to power on the appliance, you're putting yourself, your home, and the appliance at risk.

So does this mean you have to have your house--or at least parts of it--rewired? While that's the most permanent solution, it's not in everyone's budget. At this point, your best bet is to consult a licensed electrician to find out about your options, and go from there.