Why 2 pin plugs? And why so many of them?

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I've been reading the thread about the ABC Inventors show
and the Protex device and a thought raised its ugly head so
I thought I'd put pixel to screen and write.......


Just wondering from a safety point of view is a device with
a 2 pin plug safer then one with a normal 3 pin plug?

And to that end why is it that 2 pin plugs on products have so
proliferated the market?







--
John

I heard you on the wireless back in 52
We've slightly trimmed the long signature. Click to see the full one.
Re: Why 2 pin plugs? And why so many of them?



"Kate Fights, I Cry"
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**  Unless it gets damaged or wet  -  a Class 2 appliance is safer.

Items that rely on their external metal parts being connected to supply
earth become VERY UNSAFE  when that earth is missing or the AC connections
at the plug or socket are wired wrongly.  In these circumstances the
external metal work  can easily become live at 240 volts and deliver a fatal
shock !!

This  CANNOT  happen when the external metal case is not connected to the AC
power lead and is NOT being relied upon to provide a safety barrier to users
in the event of an internal electrical failure.

Also  -  the insulation that must be used and other detailed requirements
for an item to comply with Class 2 make it safe in relation to the usual
component failures and mishaps.


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**  It has taken a long time for this to become the case with most consumer
electrical and electronics.  A large part of the reason is that
manufacturing is now concentrated in Asia with a world wide marketplace  -
in that world market it is easier to get appliances approved by the local
safety authorities for sale ion each country if the appliance has been
approved already ( ie in Asia) as meeting Class 2 requirements.



 ...........   Phil





Re: Why 2 pin plugs? And why so many of them?



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Whats normal about 3 pin ? A lot of the world has 2 pin for the vast
majority of devices with only some getting three pin. (and nasty three to
two adaptors commonly available).

In australia the sockets must be three pin, extension cords must be three
pin, etc, so that a device that should
have an earth wire can get it.


2 pin devices are "double insulated".

RCD's protect  in most cases  where "protex" does and a lot of cases where
protex does not.

In fact, not adding the earth wire to the devices does ALLOW the use of
RCD's!
 The reason is  that  connecting the chasis of   many devices to earth will
create a current through earth, and then that can trip the RCD.eg a tv where
the high voltage transformer might leak a bit through the air.


The third wire on  devices is only there to allow a short to earth trip an
OVERLOAD circuit breaker or "blow the fuse".  The third wire does little to
protect people if the case of the device is broken open or the device is
dropped into water... in fact it provides a greater possibility of a lethal
circuit. SO the third wire is not put on where its no use. - plastic chassis
or 'metal chassis not exposed' devices.



Re: Why 2 pin plugs? And why so many of them?



"Brad Hogan"
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 **  Only true in places with 100  to 120 volts power.


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**  Most are  -  but some are not.

     A bedside  lamp is one example.


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**  Leaving one particular case where the Protex works when RCDs do not.


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**  Absolute bullshit.


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**  Absolute crapology.

No Class 2 device is allowed more than 1 mA leakage from AC supply to case
or chassis.



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** WRONG  -   an earthed case protects users even if the unit is soaked.

The vast majority of  Class 2 devices are not safe for use in wet areas  -
hairdryers in bathrooms are an accident waiting to happen.


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**  Shame about all those Class 2 VCRs, DVDs, hi-fi amps etc etc.

    All with metal cases and no earth in site.



..............   Phil










Re: Why 2 pin plugs? And why so many of them?


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Yikes. What counts as a Class 2? My 2-pin DVD player had 250mA @ 230v
flowing from the case, so we added an earth lead to it (Tired of getting
shocked when changing connections at the back :)).

Cheers,
Nicholas Sherlock

Re: Why 2 pin plugs? And why so many of them?



"Nicholas Sherlock"
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 **  Any appliance with the double square symbol or the words "Class 2"  or
the words " Double Insulated" on the back label.


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 **  That would be 250 uA  -  not mA  -  or you would be dead long ago.

The tingles you feel are due to very brief current spikes when RF
suppression caps of about  2000pF discharge into your skin at the moment of
contact.




..........   Phil





Re: Why 2 pin plugs? And why so many of them?



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Hell no you didnt, that would kill.

You had 230 volts open circuit, and 250mA when shorted to earth.Those
measurements are at two different times.

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Thank you Mr Sherlock.

but note, I DID NOT SET A QUANTATY!.

Phil Mr Crapology Allison did set a quantity that is the legal limit for the
leakage, as if I
* suggested that the leakage was legal
* and suggests that the leakage exceeded that limit.

He suggests that I said that the leakage was more than 1mA .

Thats the crap. I never mentioned  quantity  for the   current  leaving the
circuit.

I suggest everyone put Phil Allisison on ignore, like I did a long time ago.







Re: Why 2 pin plugs? And why so many of them?


On Sun, 8 May 2005 14:55:59 +1000, "Phil Allison"

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Russia does have a 220v 50hz supply that has a 2 pin mains setup in
domestic situations.  I have no idea if they have a system that has
the neutral and earth joined like here - or if the mains is isolated,
or some other strange system.  The plugs can be inserted in either
direction.  
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Appliances that in Australia always have an earth such as
refrigerators and irons don't have earth there.
Here are a couple of pics of a locally made domestic iron:
http://www.geocities.com/kenreed1999/SovietIron.JPG
http://www.geocities.com/kenreed1999/SovietIronData.JPG
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Domestic Stoves however did have their own dedicated socket, the pins
were thicker than an Australian plug that would tend to indicate a
15/20 amp rating, but I have no idea of the voltage or current used in
their stove circuits and didnt measure it.
http://www.geocities.com/kenreed1999/SovietStovePlug.jpg
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Russian mains plug and GPO is on the right.  on left is European plug
for comparison.  The pins are larger on euro plug, and even though
there are some euro sockets (with the side earth strips) used there,
their earth system is not connected or used with them (only 2 core fig
8 type wire is run to them) typically.
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One of the domestic metering setups I saw that had circuit breakers?
at top.  or one is RCD maybe ?   No idea.
http://www.geocities.com/kenreed1999/KWHmeter.JPG
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How devices like PC power supplies (that need an earth for the noise
filtering) cope I have no idea.
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Out of interest, regarding 2 pin appliances, double insulated and
metal cases, during the 1980's I had a Japanese made Sharp VC 488
Hi-Fi VCR.  It had substantial metal chassis throughout and a metal
case top and bottom.   All internal and external metal chassis parts
were deliberately connected together via short lengths of wire and
crimped eyelet terminals under the screws used.
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This earth setup was quite deliberately connected back to the mains
neutral via a high value resistor that was many Megs as I recall.
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The cord and plug was 2 wire, but were double insulated, and the
internal wires were coloured brown and blue
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What was the purpose of all this ?  it surely wouldnt provide any
protection in case of mains getting shorted to the metalwork, and I
fail to see what they were trying to achieve here - unless it was some
form of shielding, or to minimise hum etc ?
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Re: Why 2 pin plugs? And why so many of them?



"KLR"
 "Phil Allison"
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** That  *special safety rated resistor * is to leak away static charge that
can accrue from the antenna connection on windy day.


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** Basic electric shielding  -  same as all such units.

    The case is directly connected to signal ground.


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 **  Why did you imagine any electronics is built in a metal case ???



.............   Phil





Re: Why 2 pin plugs? And why so many of them?



"KLR"

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**  The USSR is a place that rates human life as nearly worthless  -  the
only lessons that can be learnt about safety practices from there is what
*NOT* to do.

AFAIK,  no law there allows a person to sue another or the State for damages
as a result of negligence.

Now, who was it who so accurately described the place as an "evil empire"
???




.............   Phil






Re: Why 2 pin plugs? And why so many of them?



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Look harder. Here's a copy of the Russian Federation constitution.

http://www.departments.bucknell.edu/russian/const/constit.html

Don't disparage things you know nothing of (that should shut you up for a
while :).


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// crap snipped

Was there a point to your message? Would you like to vote in USA elections,
for example?

How would anyone else feel on that matter I wonder... perhaps you wouldn't
really care, which leans toward despotism, or just a spoilt child.






Re: Why 2 pin plugs? And why so many of them?



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BAHAHAHA This is a joke right ?

I said "A lot". You mean to say insignificant populations have 240 volts and
the chasis of metal devices using neutral ???? You need to get out more.
Vietnam for example, often has everything plugged into 2 pin 240 volt
sockets.


beats me as to whether its safe to do that or not.


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Thats a requirement as the element can burn out and  create lethal  circuit
configurations "in normal use".

The chassis has to be earthed to ensure the fuse will blow  if active
touches chassis,
or neutral touches chassis and theres significant power in the circuit so
made.



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I agree. RCD  earth and no earth, doesnt do anything.

There's nothing that can be done for wet areas, except some sort of protex
system.

You talk as if  was am totally wrong.

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Ok, so the third wire is not put even if it could be some use.

Thats just a more specific statement about a different case.
perhaps I should have mentioned it, but well these things happen.

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Just remove's the sting when you touch the case.

The vcr's that DONT have this give you a sting when you first touch them.





Re: Why 2 pin plugs? And why so many of them?



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There are just circuit breakers, probably one for lights and one for power.

Tom

Re: Why 2 pin plugs? And why so many of them?


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Most if not all of continental Europe has 220-230 V power with 2 pins.
There are some devices like washing machines or fridges with 3 pin plugs
but the construction is such that you can plug them into 2 pin power
point. Most of the powerpoints in a household are 2 pin with a couple
(eg. one in the kithen and one in a bathroom) having 3 pins.


Tom

Re: Why 2 pin plugs? And why so many of them?



"Tom"
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**  So does Australia  -  most plug packs have two pins and so do most power
leads attached to Class 2 appliances.

  In all cases,  Class 2 does not use the earth pin.


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 **   Really ?     Bet that is not the case in Germany.



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** This site gives a listing of all the plugs and sockets in use.

http://kropla.com/electric2.htm


Seems all of Europe has 3 pin grounded outlets for metal cased appliances
that are not Class 2   -   as does the USA nowadays.




............    Phil





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