why we are preferring 3pin plugs in some devices?

On 16 Jun 2008 08:19:12 GMT, snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) wrote:


There is a list with images of all the EIA receptacles.
There are higher voltage models, and higher current models, and euro models. About 40 different plug/connector combos.
I don't have the link handy right now, but I dug through this sheet about a year or so ago.
Going with the standard is the way to go. anything else handcuffs your available sales region(s).
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On Wed, 11 Jun 2008 20:44:44 GMT, James Sweet

The Germans blew it all up ?
I have always said Europe and Japan got a kick start after the war because they had to build new infrastructure. We still had all of our old "plant". (particularly the "big iron" tank factories) How else can you explain why cars in the US didn't advance much from the 30's until the rest of the world kicked our ass into changing.
I suppose you are right, we do have a lot of homes wired for a "60a" world and trying to live the American "200a" lifestyle. That does tend to get back to my "extension cords and cube tap" theory.
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Andrew Gabriel wrote:

Precisely why I'd like to see some reliable statistics.

Strange, because they're more electrical appliances in use at the end, especially portable ones.

That's surprising. I wouldn't be surprised at higher electrocution figures since the US has more swimming pools per capita, and the code for electrical outlets in bathrooms anf kitchens has only recently been strengthened.

Was it the increase in "do it yourself" wiring? I hope it wasn't the inspectors getting electrocuted! :-)
There is a proposed US code change to require "arc detecting" circuit breakers in many areas. This sounds like a good idea, until one sees the problem with implementing such a device. GFCIs, (RCDs), are now common, and and are required in dangerous areas by the new codes.
See: http://en.wikipedia.org/wiki/Residual-current_device
"Use and regulations differ widely from country to country. In Europe, the UK is the only country that does not mandate the use of RCDs (however this is due to change in July 2008 for most new installations). In contrast, Germany requres the use of RCDs on ALL sockets up to 20A which are for general use. This rule was introduced in June 2007 (DIN VDE 0100-410 Nr. 411.3.3). In the U.S., the National Electrical Code requires GFCIs in bathrooms, kitchens, garages, outdoor areas, crawl spaces, unfinished basements, near wet bars, swimming pools, and spas in residential construction."
I don't mean to re-ignite, (no pun intended), the 240V vs 120V argument!
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If the initial data capture is inaccurate, there are none to be had no matter how you process the data subsequently.

There was a noticable effect around 1990, which was put down to a significant increase in HiFi/TV/Video appliances. However, the general trend would appear to be safety improving faster than the rate of increase of appliances (although that's a gross over- simplifiction).

No. DIY wiring has always been very popular here. The change in the law made it much more beurocratic, and expensive, to make safe DIY changes legally, and encourages temporary and less well designed changes. There was no evidence that DIY wiring was responsible for any of the incidents. Indeed there was much evidence that the incidents resulted from _not_ making changes and improvements to wiring when they were required. So a law to encourage temporary and less well designed changes, and to dissaude you making improvements properly, had exactly the effect many of us predicted it would, but much more drammatically than even we imagined beforehand.
I was reading that recently New Zealand reversed similar legislation they have had, and saw safety improve. I'm not familiar with local issues with New Zealand wiring, but given what we predicted and have subsequently seen here, that comes as no surprise to me.

I have to say that seems to me like the wrong solution to your arcing problem. I think you should look at the design and quality of your wiring accessories compared with other countries at similar economic levels. This just isn't a problem in most countries. An arc fault detector is a sticky plaster, and you would do better to solve the actual arcing problems, IMHO.

Do bare in mind that over half of Europe pays no attention to their wiring codes at all, so it doesn't really matter what they say. Our wiring regs in the UK have been very good for years (and have been adopted by some other countries too). However, the newest (17th) edition you refer to above has gone rather commercial now with companies managing to force their products into it without the considered risk and benefit analysis which made it a highly respected set of regs in the past. The 17th Edition regs claim to replace the 16th Edition in July 2008, but their legal force is via building regulations, which still explicitly require use of the 16th Edition for homes. So currently this is all in a mess, because the processes have been taken over by politicians and commercial concerns with their own agendas, whereas it used to be handled by real engineers who understood wiring and what safety and risk analysis is.
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Andrew Gabriel
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snipped-for-privacy@aol.com wrote:

They really ought to be grounded too. Years ago I had a halogen torchier in my office. I could swear I got a tingle several times when touching it, then one day I pulled the monitor cable off one of my PCs and in doing so the metal connector shell brushed the lamp and POW! It tripped the circuit, burned a chunk out of the connector, and left a small blob of melted metal on the lamp. I did some investigating and found that a wire had chafed where it runs through the threaded tube up at the top and the entire lamp was hot.
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On Tue, 10 Jun 2008 09:33:30 -0400 snipped-for-privacy@aol.com wrote:
| wrote: | |>why we are preferring 3pin plugs in some devices (eg.in ups,extention |>boxes...) and why we are preffering 2pin plugs in some devices(eg.in |>ordinary night lamps)? | | Anything with a metal case probably should have a ground pin, although | it is not always true.
The way a device is used might also factor in. Aside from those using a wall wart power supply with a definite low voltage barrier, computers are devices that humans regularly operate (even though the keyboards tend to be make of plastic).
The way the wiring is done internally might also factor in. A device that has a greater risk of creating a path from the hot wire to the case, or is more subject to potential damage internally, or can get wet, might need a ground wire.
But I see many exceptions to a lot of these. A friend has an electronic organ that directly connects to AC power with a 2-conductor cord that is a lot like a shaver cord. Many kitchen appliances still use ungrounded plugs.
I think a lot of it is legacy, too.
A neighboor of mine, when I was in grade school, was wiring up an antenna to a new 2nd TV. It kept blowing fuses when it was turned on. He had the TV repair guy come check it out. After blowing yet another fuse he was trying thingswith it and notice it was OK with the antenna disconnected. So he went to put the antenna back on while it was on and got to see a nice bright arc and blew another fuse. Turns out the 1st TV was the culprit and the TV antenna was "hot" and sufficiently isolated from ground that it didn't draw enough to blow a fuse or burn out the twin line. The 2nd TV had the antenna line grounded. Reversing the plug on the 1st TV was the workaround. As far as I know, they left it like that. This was in the 1960's.
I had an old shortwave radio my grandmother gave me that would have its antenna lead "hot" when the plug was reversed. My grandfather gave me an old capacitor tester when I was getting interested in electronics. I got to feel what 120V was like one time when I touched it while barefoot in the basement.
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There three classes of protection against electric shock listed in IEC/EN standards. See extracts from IEN/EN 60950-1 below:-
Class I - equipment where protection against electric shock is achieved by - using BASIC INSULATION and - providing a means of connection to the PROTECTIVE EARTHING CONDUCTOR in the building wiring those conductive parts that are otherwise capable of assuming HAZARDOUS VOLTAGES if the BASIC INSULATION fails NOTE CLASS I EQUIPMENT may have parts with DOUBLE INSULATION or REINFORCED INSULATION.
The typical electic stove, kettle etc used in Europe with a three pin plug.
Class II equipment in which protection against electric shock does not rely on BASIC INSULATION only, but in which additional safety precautions, such as DOUBLE INSULATION or REINFORCED INSULATION are provided, there being no reliance on protective earthing.
A typical electric shaver, hair drier etc, with a two pin European plug (no Earth)
Class III equipment in which protection against electric shock relies upon supply from SELV CIRCUITS and in which HAZARDOUS VOLTAGES are not generated NOTE For CLASS III EQUIPMENT, although there is no requirement for protection against electric shock, all other requirements of the standard apply.
Typical battery operated equipment.
BASIC INSULATION insulation to provide basic protection against electric shock.
SUPPLEMENTARY INSULATION independent insulation applied in addition to BASIC INSULATION in order to reduce the risk of electric shock in the event of a failure of the BASIC INSULATION
DOUBLE INSULATION insulation comprising both BASIC INSULATION and SUPPLEMENTARY INSULATION
REINFORCED INSULATION single insulation system that provides a degree of protection against electric shock equivalent to DOUBLE INSULATION under the conditions specified in this standard NOTE The term "insulation system" does not imply that the insulation has to be in one homogeneous piece. It may comprise several layers that cannot be tested as BASIC INSULATION and SUPPLEMENTARY INSULATION.
Hope the above helps.
BillB Leeds lad in exile
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