It used to be that you could plug in something and it didn't matter which pole went into which outlet hole in the wall. Now many plugs have one side slightly bigger than the other so it will only fit one way. Why is this if the current is AC and so it doesn't matter which plug goes into which hole?
2006-12-22 01:27:15 · 10 answers · asked by taotemu 3 in Consumer Electronics ➔ Other - Electronics
There are, of course, two styles of polarized plugs in the US.
One style which some posters refer to has three plugs, one of which is round -- those three plugs are "hot", "neutral" and "ground."
However, as the asker noticed, SOME US plugs are two-prong polarized. In these plugs, the right-hand-plug is larger than the left. The right hand plug then is "hot" and the left is "neutral." (These are called "type B" plugs.) The older style had two narrow blades and are refered to as "Type A" plugs.
Why polarize plugs? Because in an effort to hold down costs, the makers of some electronic equipment used what is called a "hot chassis." This was common in low end radios and televisions, and extended to other appliances. In those cases, while the appliance would WORK properly with the plug inserted either way, if the plug was in one way, it was safe to touch the bare metal parts of the equipment and the other way, it was most assuredly NOT safe to do so. So, the National Electrical Code people, and the equipment manufacturers came up with the polarized plugs.
This standard is enforced as part of the standards of the National Electrical Manufacturer's Association (NEMA) and adopted by 38 other countries, this simple plug with two flat parallel pins, or blades, is used in most of North America and on the west coast of South America on devices not requiring a ground connection, such as lamps and "double-insulated" small appliances. NEMA 1-15 sockets have been prohibited in new construction in the United States and Canada since 1965, but remain in many older homes and are still sold "for replacement use only". Type A plugs are still very common because they are compatible with type B sockets.
Early designs could be inserted either way, but modern ones prevent the neutral pin from being inserted into the live socket by making it wider than the live one, referred to as a polarized plug. (Note that this is not the same as positive/negative polarization in a direct current system.) New polarized plugs will not fit in old type A sockets, but both old and new type A plugs will fit in new type A and type B sockets. Some devices that do not distinguish between neutral and live, such as sealed electronic power supplies, are still sold with both pins narrow. When attaching a new polarized plug to a cord, it is useful to remember that the most common type of two-conductor cord for low-power use in North America has smooth insulation on the "hot" side and ribbed insulation on the "neutral" side.
2006-12-22 01:48:09 · answer #1 · answered by rboatright 3 · 0⤊ 0⤋
That is a damn good question. The answer is to keep the integrity of the polarity of the unit which you are plugging in. I am not sure about peoples explanation about grounding (earthing) though as we have a third hole in the socket for that. For example some equipment, like a vacuum cleaner (hoover) may have only two prongs on the plug, but it may be internally grounded (earthed) inside the unit. A lamp, on the other hand has two prongs and I have never seen and internal ground on a lamp and have taken many apart. Yet, they have polarized plugs. An electric drill many times will have three prongs (which automatically takes care of the polarity because the won't go in upside down. They are grounded for certain, because the third hole in the socket is a dedicated ground.
2006-12-22 01:41:54 · answer #2 · answered by Anonymous · 0⤊ 0⤋
The third rounded pole is for ground but there are plugs which do only have two poles that are keyed to go only one way. These are called polarized plugs. These are usually used in devices that connect to other electrical devices. If the two devices flipped the hot and the neutral, voltage potential could be realized between the two devices and if you touched them both at the same time, you could get a big shock! In other cases, like sound or A/V equipment you could get a lot of AC hum and picture distortion.
2006-12-22 01:32:33 · answer #3 · answered by Geoff S 6 · 0⤊ 0⤋
It is for grounding. Older plugs still have it the old way. But it is for better grounding purposes. Especially in the case of 2 prongs instead of 3.
2006-12-22 01:30:43 · answer #4 · answered by Wicked Good 6 · 0⤊ 0⤋
Many appliances have polarized plugs which are manufacturers way to help keep you safe! The larger spade is the neutral wire. Many of the newer appliances are designed so that internal circuit grounds are attached to the chassis,as is this neutral wire. This to help assure that you don't have much likelyhood of getting shocked! :-)=
2006-12-22 01:32:19 · answer #5 · answered by Jcontrols 6 · 1⤊ 0⤋
white is impartial / black is warm in case your breaker field is cord wisely. the out enable is marked on the area or decrease back for acceptable placement of wires. (you maximum remove from wall to work out markings ( close breaker off be fore you proceed )
2016-12-01 02:08:53 · answer #6 · answered by Anonymous · 0⤊ 0⤋
So that what ever you plug in is ghrounded properly.
2006-12-22 01:29:57 · answer #7 · answered by Anonymous · 1⤊ 0⤋
helps to prevent your house wiring from blowing the fuse/tripping the breaker.
2006-12-22 01:33:17 · answer #8 · answered by demonicunicorn 4 · 0⤊ 1⤋
it keeps the wires grounded.
2006-12-22 01:29:22 · answer #9 · answered by Kutekymmee 6 · 1⤊ 0⤋
one is a ground!
2006-12-22 01:29:28 · answer #10 · answered by ~*cRaCkNeSs*~ 3 · 0⤊ 0⤋