Polarized plugs work as a safety mechanism to prevent electrical shock if you touch an energized part of the appliance. They come in two forms: plugs with two prongs of different sizes and plugs with two flat prongs and a third circular prong underneath.
How They Work
Due to the design of polarized plugs, they can only be plugged into a socket in one direction, which guarantees that the live conductor and the live pole on the appliance will be connected, and the neutral conductor to the neutral pole as well. In appliances with regular plugs, if you were to touch a part that was energized, the current would travel to the ground through your body, giving you an electric shock. By having the neutral conductor and pole together, the exposed parts of the appliance are connected to a ground wire, preventing the current from traveling through your body.
When They Don’t Work
If the live and neutral wiring in the wall socket have been switched around, the purpose for polarization has been defeated. Using a circuit tester (available at most hardware stores) can tell you if this is the case. Also, many older buildings do not have polarized wall sockets, preventing the use of devices with polarized plugs. In this situation, it is best to have an electrician replace the old sockets with polarized plug accessible ones.