[aldente]

In Europe electric outlet plugs can be turned either way when inserted since the electric current is alternating. AC

In the USA the current also alters regardless of the fact that the voltage is lower and the Herz frequency differs slightly.

Why is it then that ungrounded American plugs have one enlarged finger which forces you to to insert the plug only one particular way?

http://www.lakewoodconferences.com/dire ... d_Plug.jpg

[jasonraymondson]

This is called a polarized plug, and it ensures that the plug is inserted correctly in a socket to reduce the risk of electrical shock.


Now where is my million dollars

[Mechman]

albente,

Be careful what you ask for, you might get it and not like it. The short and simple version is the the Europeans picked some bad choices that in todays world would be considered local but not optimal, dangerous and Darwinistic (young, stupid and uncareful people should not be using electricity).

For the USA 120VAC, the large flat plug is not AC power but generator ground (white - not hot and somewhat safe ground) which is very close to local earth groung (green - eco green for earth). The small flat plug is hot 120VAC (Root Mean Squared) RMA and is generally a black wire (black as in black death - literally) with about 160Volts sinewave peak to peak. The use of the polarized plug is to keep you safer. If you have an electrical appliance you want to ground the outside case or at least internal electrical frames to ground (green if available in a three prong socket or white if that is all you have with the USA polarized plug). That polarized plug is set up to save your life if there is a failure in the device and you want to safely route the deadly power of the black 120VAC line to ground (white or green ground) instead of through you body which might kill you. With the European set up you are not sure there is a safe ground without a third wire. If the European 240VAC is setup up like the USA 240VAC highpower outlets (hardwired or always 3 or 4 plug sockets so a generator neutral or a generator neutral and a ground is always available for safety) you have arm 1 at 120VAC which is running opposite 180 degree phase from the arm 2 at 120VAC giving you a combined 240VAC. If Europe uses 240V on one plug wire (Black?) and generator neutral (white?) you cannot be sure the case of the device has a ground since the plug is reversable and you have 240VAC at a single point failure (dangerous - see below). If Europe uses two 120V lines for lower single point failure voltage, you now have no safety ground with a two wire plug. Either way, the 240VAC is less safe that a single 120VAC with a generator ground. Also 240VAC requires twice the insulation for safety.

The use of 50 Hz in Europe compared to 60 Hz in the USA means the 50 Hz capacitors and transformers have to be bigger and heavier than the 60 Hz equivelent. Aircraft use 400 Hz to greatly reduce the weight. High frequency is better for AC use. The very good European high speed trains use a couple of 1000 Hz for optimal performance with current technology.

It always bothers me in Europe when you plug in a device and the socket blows a big blue arc the instant you connect up. Again this because 240VAC has four times the power charging up the same capacitor or inductor that 120VAC.

The USA was truely blessed by two great people (Tesla and Edison)at the developement of electrical distribution and we figured out many of the issues before governement and industry locked in something less than optimal for the user environment. In the battle of 120/240VAC at 60Hz vs 240VAC at 50Hz, the USA choice was wiser in both voltage selection and frequency. 120VAC is lethal but you might be able to have a minor accident without injury but the 240VAC is very dangeous compared to 120VAC. 240VAC will dump power at four times the rate for the same resistance setup (accident). 240VAC is twice the voltage so you are more likely to not be able to let go or escape the accidental contact. The USA does have 240V service for high power devices like stoves, dryers, A/C but these are rarely unpluged and the dangeous voltage of 240VAC is rarely exposed to the typical person.

Let do a run down:

1. 240VAC is significatly more dangerous than 120VAC per accident
2. 240VAC requires twice the insulation compared to 120VAC for safety
3. Polarized plug provides neutral/ground not available always available in unpolarized plug
4. 50Hz devices that use capacitors and inductors/transformers are not as efficient per mass compared to 60Hz, 400Hz, or higher
5. 50Hz lights are more likely to have a visible flicker than 60Hz or higher resulting in eye strain.

Sorry but the European standards locked in sucky electrical standard even if they appear simple and reversable. At least you have the Metric system which is great for most applications and good trains which are electric but don't use 240VAC 50Hz.

Mark

[MD]

Good reply mark, except the p-p value is 320-340 v, not 160. You only counted the half wave.

(details....details...)

[Mechman]

MD, thank you for the correction of my peak to peak instead of zero to peak error, details are important. I did not have time to properly spell check and grammar check and detail check my post before I had to go to work. Now that I am back I have found and fixed my multiple errors. Thank you for your help and patience.

(Revision 1 of post)

albente,

Be careful what you ask for, you might get it and not like it. The short and simple version is that the Europeans picked some bad choices that in today’s world would be considered local but not optimal, dangerous and Darwinistic (young, stupid and uncareful people should not be using electricity).

For the USA 120VAC, the large flat plug is not AC power but generator ground (white - not hot and somewhat safe ground) which is very close to local earth ground (green - eco green for earth). The small flat plug is hot 120VAC (Root Mean Squared) RMS and is generally a black wire (black as in black death - literally) with about 160Volts sinewave zero to peak (or about 320 Volts peak to peak -MD). The peak voltage is higher that the RMS voltage so 120VAC is more dangerous than just 120VDC. The use of a polarized plug is to keep you safer. If you have an electrical appliance you want to ground the outside case or at least internal electrical frames to ground (green if available in a three prong socket or white if that is all you have with the USA polarized plug). That polarized plug is set up to save your life if there is a failure in the device and you want to safely route the deadly power of the black 120VAC line to ground (white or green ground) instead of through you body which might kill you. With the European set up you are not sure there is a safe ground without a third wire. If the European 240VAC is setup up like the USA 240VAC highpower outlets (hardwired or always 3 or 4 plug sockets so a generator neutral or a generator neutral and a ground is always available for safety) you have arm 1 at 120VAC which is running opposite 180 degree phase from the arm 2 at 120VAC giving you a combined 240VAC. If Europe uses 240V on one plug wire (Black?) and generator neutral (white?) you cannot be sure the case of the device has a ground since the plug is reversible and you have 240VAC at a single point failure (dangerous - see below). If Europe uses two 120V lines for lower single point failure voltage, you now have no safety ground with a two wire plug. Either way, the 240VAC is less safe that a single 120VAC with a generator ground. Also 240VAC requires twice the insulation for safety.

The use of 50 Hz in Europe compared to 60 Hz in the USA means the 50 Hz capacitors and transformers have to be bigger and heavier than the 60 Hz equivalent. Aircraft use 400 Hz to greatly reduce the weight. High frequency is better for AC use. The very good European high speed trains use a couple of 1000 Hz for optimal performance with current technology.

It always bothers me in Europe when I plug in a device (my laptop) and the 240VAC socket blows a big blue arc the instant you connect up compared to 120VAC in the USA. Again this because 240VAC has four times the power charging up the same capacitor or inductor that 120VAC on the power supply even though it is rated for 240VAC 50Hz.

The USA was truly blessed by two great people (Tesla and Edison) at the development of electrical distribution and we figured out many of the issues before government and industry locked in something less than optimal for the user environment. In the battle of 120/240VAC at 60Hz vs. 240VAC at 50Hz, the USA choice was wiser in both voltage selection and frequency. 120VAC is lethal but you might be able to have a minor accident without injury but the 240VAC is very dangerous compared to 120VAC. 240VAC will dump power at four times the rate for the same resistance setup (accident). 240VAC is twice the voltage so you are more likely to not be able to let go or escape the accidental contact. The USA does have 240V service for high power devices like stoves, dryers, A/C but these are rarely unplugged and the dangerous voltage of 240VAC is rarely exposed to the typical person.

Lets do a run down:

1. 240VAC is significantly more dangerous than 120VAC per accident
2. 240VAC requires twice the insulation compared to 120VAC for safety
3. Polarized plug provides neutral/ground that is not always available in unpolarized plug
4. 50Hz devices that use capacitors and inductors/transformers are not as efficient per mass compared to 60Hz, 400Hz, or higher
5. 50Hz lights are more likely to have a visible flicker than 60Hz or higher resulting in eye strain.

Sorry but the European standards locked in a sucky electrical standard even if they appear simple and reversible. At least you have the Metric system which is great for most applications and good trains which are electric but don't use 240VAC 50Hz.

For a little extra details: 24VDC or VAC is about as safe as you can touch without special protection. You can let go of 32Volts DC when wet but that is about the limit of safety. 24Volts AC approaches 32 Volts zero to peak but does have the benefit of a zero voltage crossing so you have a chance to let go. VAC is generally slightly safer zero to peak compared to DC (direct current) for the same voltage but VDC is generally slightly safer per volt when compared to VAC RMS. However, large DC current arcs are hard to suppress because of the constant current compared to the zero voltage crossing of AC currents. If the safe limit is 24VAC, you can imaging the danger of 120VAC and 240VAC.

One of my coworkers, Bob, worked at Westinghouse long ago and they got an old generator made by Westinghouse that needed rebuilding and rewinding. They looked at its specifications and the voltage and current ratings were weird. They wondered what this generator was for. The outside of the shipping crate had a ship from address of the New York Prison system and then they realized what the generator was for. One of the workers then commented, “Oh, this generator is designed to start with a person on the line”. This generator was the execution generator for the New York Prison electric chair. It was designed to intentionally generate the higher voltages and currents needed to kill someone.

Have a good one and stay safe with electricity. : )

[Twilight]

I like the British three-pin plug; live, neutral, earth, with the earth pin 5mm longer, you can be fairly sure with those. To be fair, European domestic wiring now incorporates earth contacts, but the old two-pin unearthed makes me uneasy. As for the rest, I guess we have to live with our design compromises. It could be worse, I dread to think what the specs must be on domestic electrical appliances in India. Imagine trying to make a fridge that works at voltages from 50V to 500V, with a current range to match, in a wide frequency range, without catching fire or killing the user. I bet they keep a box of fuses in a cupboard with the matches.

By the way, I have my screen refresh set at 75Hz otherwise I see the flicker. I'm glad it even came with that option. 50Hz sucks for display and 60Hz isn't good enough either.

[Denny]

Perhaps the strangest electrical frequency was 25 hz., which was used in upper New York State in the early 20th c. and most of Ontario province in Canada until the late 1950's. I had a late relative who worked on the Ontario Hydro Commission team which converted all appliances with motors (even clocks!) over to 60 hz., town by town, city by city.

I never did find out why they selected 25 hz in the first place, I think he said it went way back to about the year 1900 when the first hydroelectric dams were installed at Niagara Falls, providing the juice which powered the great Buffalo Exposition of Progress.

By the way, one good reason that most of the world uses 240 v rather than 120 v for most home wiring is that you can use wiring of just half the gage for the same power capacity, both in the home and the appliances. We North Americans have never been shy in our use of resources.

[aldente]

I have to do some more homework on this since so far I am simply an end user, consumer and blind slave of this widely distributed product called electicity in the first place.

The US of A are a very strange place no matter what. Always Cowboy, always oppsing metric, always doing their own thing.

An extension of good old historic England....

War of Currents

[Kingcoal]

There is a long story as to how the polarized plug came into existence. The short story is that back in the 50's and 60's, the design of a lot of low end electrical products was haphazard by modern standards. The polarized plug was invented to make sure that the device, generally a cheap TV set, stereo, etc, could only be plugged into an outlet which is polarized (a lot of old house wiring didn't even use polarized outlets.) These cheap products with polarized plugs didn't have a transformer to provide isolation in their main power supply. Instead, they would simply connect the AC neutral wire directly to the metal chassis! By modern electrical engineering standards this is not only considered dangerous, but criminally negligent. The problem occurred when for some reason, the plug either got plugged in reversed, or the outlet was reversed (a common problem back in the day.) In this condition, the hot AC line was now connected to the chassis and your electrical product was now "hot" and you could get a shock if you touched it and somehow completed a circuit to ground. Higher end products had transformers and omitted the polarized plug. Other types of products, such as table lamps didn't need to connect any conductors to the chassis, so they were safe.

Since the 70's and the establishment of the National Electrical code and the Underwriters Laboratory, the two prong, polarized plug is something of an artifact. In modern equipment, if the chassis is to be grounded, then a three prong plug is used. The third prong is connected to earth ground only in the house wiring. Modern electrical engineers don't even trust that, so items such as hair dryers and power tools are made of plastic and are "double insulated" so that the user has absolutely no possibility of coming in contact with any conductors. A lot of medical equipment uses grounded metal chassis and the standards for those are very strict, but that's beyond the scope here.

A two prong, non polarized plug can be safe if the products plugged into it are double insulated. Double insulation is an industry term for a design standard which insures that there is no way that anything touching the outside of the product can make connection with an AC conductor.