Why Are the Holes in My Outlets Different Sizes?

If you look closely at an electrical outlet, you might notice a peculiar detail: the two long, thin slots are not the same size. One of the two blades is slightly wider at the tip than the other. If you try to push the large prong into the smaller hole, it won’t fit. Why is that? Why not just make all plugs reversible in order to make plugging things in easy? It would be incredibly convenient, especially for some of the larger power bricks that are included with some of our gadgets these days.

There is an extremely valuable reason for this: safety. Almost anyone knows that the electrical power running through your walls could be dangerous if mishandled, and the design of our outlets is engineered to prevent accidental mishandling of power that could cause serious injury.

Why Are Outlet Plugs Different Sizes?

Every electrical circuit has two sides: a hot side for the energized wire where power travels from the electric lines to your outlets for consumption and a neutral side which is used to complete a circuit and allow you to use the power.

Let's use a simple device like an electric lamp as a demonstration. Lamps are set up so that the switch on the side of the lightbulb socket connects or disconnects the power by connecting or disconnecting the hot side of a circuit. The hot line is connected to a small pin at the back of the socket, while the metal threaded piece is the neutral side. However, instead of the small pin at the back of the lightbulb socket being the hot side as normal, when you plug a device in backward the threaded socket becomes energized and functions as the hot side. This could be dangerous because this metal socket is much easier to accidentally touch, which can cause a pretty serious shock.

Therefore, engineers came up with the idea to make the neutral blade on each plug slightly wider than the hot blade and to make the hole for the neutral blade in each outlet slightly wider than the hot side.

What About Plugs with Blades the Same Width?

If you’ve paid attention, you might have noticed that you have a few devices that can be plugged in either direction because both blades on the plug are the same width. Wouldn’t this be incredibly unsafe? Not necessarily. While it could potentially be unsafe for something like an AC-powered lamp, devices that require DC current need to invert the incoming power from your wall before it can be used in the first place. These devices run AC power through a circuit known as an inverter in order to create DC power that is then used by the device itself (often at a much lower voltage).

Because of the alternating nature of alternating current, electrical current flows equally in both directions, so it really doesn’t matter what prong your charger gets the power it uses from. Because it is all going through this same rectifier circuit, it all gets inverted to DC exactly the same, and thus there is no danger to plugging it in with the prongs in either hole of your plug.

What Does the Third Outlet Prong Do?

Most of your plugs probably have a third, smaller, semi-rounded prong located at the bottom of the plug, in the center between the two blades. This third prong is for the ground post, and it too is an important safety feature:

  • Your ground circuit is tied to your neutral circuit at your home’s breaker box or main electrical circuit, creating a sort of “safety valve” for your electrical system.
  • If a short or fault occurs in a device, the ground prong creates a path of very low resistance that power can use to get back to your main electrical panel and then into the ground through your electrical service's grounding system.

Why Do Some Plugs Not Have 3 Prongs?

Some plugs or devices will not have 3 prongs because not every device will need it. For example, devices that are certified as "double insulated" are not required to be grounded. In these cases, it is safe to use just two prongs.

However, if you have a device with a third prong, you should never cut it off or “delete” it in order to fit it into a two-pronged outlet. This could potentially be dangerous and cause fire or injury.

Are you concerned about an outlet in your home? Looking to improve safety by modernizing your equipment or upgrading your breaker panel? Make the call to the electrical team at A-TEMP Heating, Cooling & Electrical at (503) 694-3396 today.

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