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Name: Gene U.
Status: Other
Age: 40s
Location: N/A
Country: N/A
Date: 2002


Question:
Why are there polarize and unpolarized plugs for electrical devices, like drills, toasters, blenders, radios, etc for 120 volts? What could happen if there were to be a problem, like a internal short circuit?



Replies:
Polarized plugs are used to connect the most exposed part of an appliance to the ground wire so that if you are touching a ground (like a pipe, bathtub, faucet, etc.) and the exposed part of an appliance (the case, the threaded part of a light bulb socket, etc) you will not get an electrical shock. Many appliances, such as electrical drills, are now "doubly insulated" so the probability of any exposed part of the appliance being connected, by a short or other problem in the appliance, to either wire is very small. Such devices often use unpolarized plugs where the two prongs of the plug are identical. On a polarized plug, the ground prong is larger.

Polarized plugs are a safety feature, but certainly not an infallible one. "Ground fault" circuit breakers, which break the circuit for both wires when there is an indication of a possibly dangerous problem provide much greater safety. They monitor the difference in the current in the "hot" wire and the "ground" wire. If the currents differ by as little as 0.005 amperes, they break the circuit in as little as 0.025 seconds. This is adequate protection to keep a person from getting a dangerous shock. The difference in currents could be caused by a person touching the hot wire and a faucet, thereby sending some of the current directly to "ground" instead of back through the "ground" wire.

Best, Dick Plano...

October 2013 A corrective note should be added:

?The other reply is not totally correct. The larger slot in an outlet is called the neutral and is not the ground. The ground is the rounded hole offset in the middle of an outlet. Thus a polarized plug is used to connect the most exposed part of an appliance to the neutral wire, not to the ground wire. Also, the term is ?double insulated? not ?doubly insulated.?

In the event of an actual short circuit in the appliance there will be a large current draw and the protective device, either a fuse or circuit breaker in the panelbox, will open and interrupt or stop the current flow. As the respondent correctly notes, the danger to the user is if the user contacts an energized part of the appliance and has a current flowing through him or her.

As a side note, in professional electrical circles, the ground wire is called the ?grounding conductor,? the neutral is called the ?grounded conductor,? and the hot is called the ?ungrounded conductor.?



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