wall outlet shapes

[jjoensuu]

Not meaning purposely to ask silly questions, but is there an engineering rationale for the wall outlet shapes (for electrical power) used in various countries?

For example, why does U.S. use a system where one of the two holes is larger than the other? Is this so that circuitry plugged in does not necessarily require a diode bridge? (yes, you may see that I do not know that much about electronics)

On the other hand, in continental europe the system with two round prongs enables the rotating of the plug. And Australia then again uses a system with two or three holes placed so that the plug can not be rotated.

Just wondering if there may have been technical reasons for why a specific shape was chosen?

cheers...

 

[itsmoked]

USA plugs have a smaller slot to denote the HOT contact as compared to the other slot which is the NEUTRAL. The other 'smile' contact is of course ground.

The power is supplied as alternating current so the bridge question is indeed wrong.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[jjoensuu]

thanks itsmoked,

but why does U.S. want to mark one contact as hot and one as neutral?

who benefits from it? the technician, electronics manufacturer or the consumer?

In continental Europe both holes are the same size.

cheers...

 

[MikeHalloran]

In Europe, both holes are equally dangerous.

The smaller hole around the 'hot' contact makes it harder for a child to get stung by, say, putting a bobby pin in the socket. [I was two years old.]

US outlets didn't always have a ground connection. The two-wire sockets are 'polarized' with asymmetrical pins to provide a small degree of safety, I think. I don't think that they always were.

If you look closely at the insulation system within an old electric lamp socket, comprising mostly paper, you can appreciate that the safety of the system is (marginally) enhanced by connecting the bulb socket shell to neutral, which makes it slightly less dangerous to touch the exposed metal at the base of the lamp envelope.

[ Two-wire 'zipcord' cable is also polarized. Close examination will reveal a slight 'fin' along one wire. ]

Speaking of the hazard associated with the exposed metal at the bulb socket, if lamps and plugs were not polarized and standardized, and since only the center contact of the socket is switched, it would be possible to grasp two lamps at random and become a, er, dead short.






Mike Halloran
Pembroke Pines, FL, USA

 

[itsmoked]

Some devices had chassis that were hooked to one of the two prongs,(notably TVs), this meant the chassis could be live, (HOT), and therefore dangerous or NEUTRAL and therefore 'safer' to touch. By polarizing the plugs and outlets the chassis' could be prevented from being HOT.

In reality because so many lamoid electricians mix the two sides up when wiring outlets, the product manufactures still have to assume reversed operation, and build their products accordingly.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[jjoensuu]

cool, thanks for your clear answers

 

[ScottyUK]

In Europe, both holes are equally dangerous.

Really? Why?

Most of Europe runs a phase/neutral/earth system to domestic and light commercial premises. The phase conductor is clearly dangerous, but the neutral is solidly bonded to earth either at the substation or service entrance (or both in a PME system) and therefore has a significantly lower level of danger compared to the phase conductor, so your comment seems a little strange.


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Sometimes I only open my mouth to swap feet...

 

[MikeHalloran]

Sorry, I thought they were both hot.



Mike Halloran
Pembroke Pines, FL, USA

 

[ScottyUK]

No, that's a North American thing with the centre-tapped 120-0-120V (I think!)

One of the peculiarities of the UK system is the use of fused plugs, maximum 13A, on domestic 240V supplies. Industrial 240V plugs range from 16A to (at least) 63A and are unfused. I'm not aware of any other nations who have a fused plug.


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Sometimes I only open my mouth to swap feet...

 

[rmw]

MikeHalloran,

I was more like 3-4 yrs old and I used a key. Still remember it, and remember an aunt body tackling me off of it.

ScottyUK,

Is the UK plug deliberately tight, or did it have something to do with the adapter plugs I had to use. I had some plugs that I thought I was going to have to go find Charles Atlas to help me get them plugged into the wall socket. Also, I often would forget that there is a rocker switch that has to hot up the recpticle. Most of what I used power for was a laptop, so after a while I would notice that I was on battery and not shore power.

rmw

 

[ScottyUK]

Deliberately tight? A few brands are tight when they are new - MK's Logic Plus range being one that is widely used in commercial installations that springs to mind. Other than having high contact pressure to keep I[sup]2[/sup]R losses low, and the requirement to have shuttered live and neutral holes, I see no reason why they are designed to be tight.

If you try to force a two-pin device into a UK socket you might want to invest in a hammer instead the services of Mr. Atlas (is he still alive BTW?). The sockets are designed such that longer earth pin enters first and displaces a sliding shutter mechanism to unmask the live and neutral holes. If the earth pin isn't present it will be either difficult or impossible to force an adaptor in. It is possible to open the shutter with judicious use of a screwdriver or other similar implement. Insulated objects are recommended for obvious reasons, or better yet just don't do it!

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Sometimes I only open my mouth to swap feet...

 

[MacRae]

"Quote:
In Europe, both holes are equally dangerous.

Really? Why?

Most of Europe runs a phase/neutral/earth system to domestic and light commercial premises. The phase conductor is clearly dangerous, but the neutral is solidly bonded to earth either at the substation or service entrance (or both in a PME system) and therefore has a significantly lower level of danger compared to the phase conductor, so your comment seems a little strange.

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Well, actually Mike is not that far off. Some places in Europe used to ditribute power in a 127/220 Volt three phase WYE configuration. In order to get 220V at the socket, they were wired across two of the three phases. Thus, both wires were hot, 127 volts to ground. This sytem is being phased out, in favor of the standard 220/380 volt (technically 230/400V now) system with 220V hot to neutral.

Ian Rines
Harris Corporation
Palm Bay,FL

 

[MacRae]

"This sytem is being phased out, in favor of the standard 220/380 volt (technically 230/400V now) system with 220V hot to neutral."

Sorry I meant to end that .....with 220V grounded neutral.

Ian Rines
Harris Corporation
Palm Bay,FL

 

[ScottyUK]

Just curious: which places? I'm guessing it must be eastern or southern Europe.


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Sometimes I only open my mouth to swap feet...

 

[MacRae]

I can't remember exactly where offhand, I seem to recall the Belgium/Luxembourg area.

Ian Rines
Harris Corporation
Palm Bay,FL

 

[MacRae]

I found some more info turns out it was used in quite a few countries in Europe at one time. Here is a quote from my friend Paul on another discussion forum that I visit often:

"Thanks C-H. I hadn't realized that 127/220V 3phase was also used in Sweden, although I know it was employed in some other parts of Europe, e.g. France and Spain."

I think that he is refering to very old systems ie 1950's and older.



Ian Rines
Harris Corporation
Palm Bay,FL

 

[ScottyUK]

Interesting - thanks. I wasn't doing much electrical engineering back then

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Sometimes I only open my mouth to swap feet...