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. 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. Since , ungrounded type A outlets are not permitted anymore in new constructions in the United States and Canada, but they can still be found in older buildings.
Type A and B plugs have two flat prongs with often, but not always a hole near the tip. If you were to take apart a type A or B socket and look at the contact wipers that the prongs slide into, you would find that in some cases they have have bumps on them. This prevents the plug from slipping out of the socket due to the weight of the plug and cord.
It also improves the contact between the plug and the outlet. Some sockets, however, do not have those bumps but just two spring-action blades that grip the sides of the plug pin, in which case the holes are not necessary. There are also some special outlets which allow you to lock the cord into the socket, by putting rods through the holes.
In this way, vending machines and the like cannot be unplugged. Moreover, electrical devices can be factory-sealed by the manufacturer using a plastic tie or a small padlock through one or both of the plug prong holes. The user cannot plug in the device without removing the tag, so the user is sure to see the tag. It has two flat 1.
A plug with two prongs of the exact same shape and size is considered non-polarized. You cannot tell which prong is the hot side and which is the neutral side, because the metal pins are the same. When plugged in, the electricity enters your plug through the hot wire prong and then exits through the neutral prong, to complete the circuit.
You can see, in the image above, on a polarized plug on one side is a straight blade pin and the other has a more rounded end on the pin.
The rounded end of the pin is there so you cannot insert the plug into the connector incorrectly. The best way to tell if your plug is polarized or not is to look at it. If the 2-prong plug has two equally sized pins, as shown in the image above, then it is not polarized.
The 3-prong design has a grounding pin which is designed for extra safety measures in electrical devices like a coffee pot, where they may come across liquids. The grounding pin will trip the breaker if the water gets into the circuit, stopping your equipment from running.
Non-polarized outlets were common in older homes, changing any non-polarized outlets you may have in your home will keep your house current on safety codes.
Every outlet should be replaced with a polarized outlet in an up-to-date home sale and for safety. That accounts for that fuzzy feeling in some lamps for example. If you touch this "hot" appliance and a sink faucet, even with the switch off, you could still get a shock. That is one of the basic reasons we have polarized plugs -- one fat and one thin.
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