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Re: Tingles from DVD players


On Thu, 23 Mar 2006 12:05:21 +1100, "Phil Allison"

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Fair comment. You have chosen to delete part of your previous post to
which I was replying. I'll put it back in.

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Your use of a hyphen before "so just ignore the issue." led me to
believe that was your view. On reading it again I realise you were
attributing that to the manufacturers. That sentence would have been
clearer with a comma or even no punctuation there.
My apologies for misunderstanding.


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Which is exactly why there is no prohibition on interconnecting
earthed and double insulated home entertainment equipment.

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As in my other post, the legal liability arises from miswiring a plug,
not from interconecting different classes of equipment.

--
Regards
Malcolm
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Re: Tingles from DVD players



"Malcolm Moore"
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**  That does not make even the slightest sense.

      A complete non sequitur.



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**  Many other ways for the same outcome to occur.

 Class 1 items rely on the earth wire to prevent shock in case of internal
failures.


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** One seriously compromises the safety of a class 2 item by connecting its
metal case to a class 1 item.

Same as  "de-earthing" a class 1 item *seriously* compromises its safety in
the event of some internal failure.

Go figure out why class 2 was ever invented.




.........   Phil



Re: Tingles from DVD players



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Ok, I can see that wiring the plug of the class 1 device wrongly has made
the class 1 device as well as the class 2 device dangerous to touch.  I
think that the user was pretty much asking for a jolt whether or not the
class 2 device was connected (or even existed at all), but in principle I
see why the manufacturer of the class 2 device would not want the two
devices interconnected, so the user gets electrocuted whilst touching the
device made by someone else, that would be cheaper in court....

The root cause of the problem is of course having someone who thinks they
can wire a plug but cannot.  The problem is they might not be the one to
get killed, it'll be the neighbour's kid or something like that.

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Thanks, that's the first "class 2 is safer" argument that makes sense to me.
In the context of incompetent and/or amateur electricians, no ELCB, and no
regular testing of power socket wiring and portable appliance testing, I
can see that advantage of class 2.  Those conditions are probably fairly
common too.

Chris


Re: Tingles from DVD players



"Chris Jones"
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** Not just one device, but an entire hi-fi system INCLUDING the damn
speakers !!!


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**  A third party could be the one electrocuted -  maybe a small child.


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** The makers of the class 2 devices are not liable in such a case.

Their items are not permitted to be connected to the earth system of
another.


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**  Millions of them around.

 Heaps of places sell 3 pin plugs to the public.


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** The punishment for mis-wiring a plug ought not be the death of anyone.



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** The most common cause of electrocution in the home is ( or was until
recently)  incorrectly wired plugs and extension leads.

The worst electrocution trap in where BOTH miswired but BOTH work OK unless
the two meet up.

1.  The extension lead has active and neutral wires reversed,  earth is
wired OK ( most consider this to be harmless).

2.  The appliance has earth and neutral wires reversed, active is on the
correct pin ( appliance works fine in normal outlet).


When appliance "2"  meets lead  " 1"  ?????

Death to a toddler.



.......  Phil





Re: Tingles from DVD players



I might as well add my $0.02 worth here too.

"Russ_Verdon" <verdonsATtpgi.com.au> wrote in message
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This is a well known and allowed for condition in safety standards.  It is
referred
to as "touch current" and was previosuly referred to as leakage current.  The
safe
limit for touch current in Class 2 devices is 0.25 mA and this lies within the
perception range for some people.  Touch current is likely due to the current
passing
through small value capacitors connected between the chassis and the primary
power circuits.  This is usually for ESD (electro-static discharge)
compatibility in
the case of audio/video equipment.

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There is no rule in the safety or wiring standards that prevents you from
doing so, but introducing an earth is not a good idea since it may cause
unintended earth loop currents to flow through other circuits. This can lead
to humm and noise, etc.

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Among other reasons, it also has to do with cost, but not as you might imagine.
By floating the chassis there is no need to use audio baluns or isolating
transformers in the input and output interconnection stages to remove
extraneous circulating supply currents or to provide electrical safety.

I read some of the other replies and would also like to add the following.

1.  There is no prohibition on interconection of Class 1 and Class 2 equipment.
The only safety related condition is that any earthing required for safety of
the
Class 1 device is maintained at the desired level.  Which is 1.6 times the
rated
current of an inherent protective device (eg. internal fusing).

2.  Equipment that was marked "Do Not Earth" was often done so because the
internal circuitry was "live" and separated from accessible conductive parts by
double/reinforced insulation.  Earthing the internal circuitry would be
potentially
hazardous in this case.

More commonly the "do not earth" instruction is for when the equipment is
supplied to countries that do not have the MEN (TNC-S) mains supply wiring
scheme.  In those countries there is a separate earthing terminal or bonding
point
on the equipment chassis, and more often than not, no mains plug is supplied on
the cord.  Equipment that is to be earthed has a plug added, and the chassis
bonded to
earth at the time of installation.  For floating chassis devices the do not
earth instruction
is to specifically draw attention to not to bond to earth.

3.  For small A/V and ITE, making Class 2 equipment costs almost the same as
Class 1
equipment.  Class 1 is of benefit in high power appliances like toasters,
ovens, etc.

4.  Class 2 construction does not mean double insulation.  Double insulation
may be a
type of Class 2 construction but reinforced insulation is now more common.

5.  Someone mentioned triple insulated wire is not common.  It is now very
common,
being the preferred method to construct very small footprint concentric wound
transformers in smal SMPSUs.  The majority of mobile phone power supplies I
have examined (say, since 2000) use triple insulated wire as the secondary
winding.
This way the static screen and the primary can be conductively coupled,  doing
away
with the additional layers of insulation that would otherwise be needed.

Most of the above can be found in AS/NZS 60065 and/or AS/NZS 60950-1



Re: Tingles from DVD players



"David, not to be confused with the other Davids."
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** Of course there is !!

A Class 2 appliance must not be earthed or it ceases to be one.



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**  There is.

A Class 2 appliance must not be earthed.


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** You are just making this crazy drivel up.

The earthing requirements for a class 1 appliance relate to the copper cross
section of the earth wire used,  ie must not be not less than 1 sq mm.  (
AS3100)



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**  Plenty of class 2 items are  labelled "Do Not Earth" where no such thing
existed.

( snip more irrelevant drivel )


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** Correct  -  but the names have become synonyms as far as categorising an
appliance is concerned.




.......  Phil



Re: Tingles from DVD players


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the prohibition on earthing class 2 appliances does not relate to
consumers plugging them into class 1 appliances, but to technical
personnel adding 3-pin plugs/wires.

as long as nobody fiddles with the mains connection, one is free to
earth as many inputs/outputs as one wishes.

Of course hooking the jacket of your video out RCA connector to, say,
Phase would be a fairly dangerous thing to do, but then so is poking a
knife into a toaster while its operating.


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Re: Tingles from DVD players



"Terry Given"


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** Yawn .......

A safety risk is created by so doing -  possibly a very serious one.




.......  Phil




Re: Tingles from DVD players



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Well, you'd think Toaster Boi would know about that one. :P



Re: Tingles from DVD players


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You are correct for a transformer based power supply device such as a
plug-pack, but this is not necessarily the case for other products.  The
deliniation between Class 1 and Class 2 is becoming very grey.  Whereas AS3108
and AS/NZS61558-1 say any transformer that has an earth terminal must be
classified as Class 1 other standards do not.

Definition and references below from AS/NZS60950-1, since I happen to be using
it at the moment. Note the use of earthing is not prohibited, just that the
safety strategy of the design must not rely on the protective earth.  This
standard might/is be used for a switch mode PSU plug-pack.

=====
"COPYRIGHT"
1.2.4.2 CLASS II EQUIPMENT: 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.
=====

There have been many changes since the old AS3108 and AS3100 type standards
existed as the sole point of reference.  None of those standards took into
account EMC filtering or stray currents due to SMPSU, etc.  With the more
modern standards you can certainly use Class 2 construction, with functional
(not protective) earthing.  Note, connecting an earth does not automatically
make it Class 1 in this standard.

If you want to split hairs on the issue over the Class 2 box-in-box marking,
perhaps I should of said before to scatch off the symbol.  It is then
functionally earthed Class 2 construction.  It can only be truly Class 1 if the
earthing is protective.  There is no marking to define these products (yet).
The mis-wiring of plugs etc is not a factor taken into consideration.

Here is a reference from the same standard:

======
"COPYRIGHT"
2.6.2 Functional earthing
If FUNCTIONAL EARTHING of accessible or other conductive parts is necessary,all
of the
following apply to the FUNCTIONAL EARTHING circuit:
- the FUNCTIONAL EARTHING circuit shall be separated from parts at HAZARDOUS
VOLTAGES
in the equipment by either:
.DOUBLE INSULATION or REINFORCED INSULATION or
. a protectively earthed screen or another protectively earthed conductive
part,
separated from parts at HAZARDOUS VOLTAGES by at least BASIC INSULATION and
- it is permitted to connect the FUNCTIONAL EARTHING circuit to a protective
earth terminal
or to a PROTECTIVE BONDING CONDUCTOR and

<snip a lot of stuff that isn't relevant to the argument>
=====================

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1.0 sq mm for 10A cords up to 2 metres long and 1.5 sq mm for 10A cords longer
than 2 metres.

I did make a mistake with the multiplication factor, it is 1.5 and not 1.6
times.  I am not making it up - sometimes I think it would be easier to
understand if I did.  For functional earthing there is no size requirement
other than that needed for it to do the intended job.  For protective earthing
and bonding you can provide the minimum conductor sizes in the standard (1.0 or
1.5 sq mm), or use the minimum size conductor that meets the following:

==============
"COPYRIGHT"
2.6.3.3 Size of protective bonding conductors
PROTECTIVE BONDING CONDUCTORS shall comply with one of the following:
- the minimum conductor sizes in table 3B (see 3.2.5);or
- the requirements of 2.6.3.4 and also,if the current rating of the circuit is
more than
16 A,with the minimum conductor sizes in table 2D;or
-for components only,be not smaller than the conductors supplying power to the
component.
The current rating of the circuit used in table 2D and in the test of 2.6.3.4
depends on the
provision and location of overcurrent protective devices and shall be taken as
the smaller of
a)or b)as follows.
a)The rating of an overcurrent protective device specified in the equipment
installation
instructions to be installed in the building installation wiring to protect the
equipment.?47
b)The rating of an overcurrent protective device in the equipment that protects
the circuit
or part required to be earthed.
For PLUGGABLE EQUIPMENT TYPE A and if neither a)nor b)is applicable,the current
rating of
the circuit shall be taken as the RATED CURRENT of the equipment or 16
A,whichever is
greater.
=================

So (b) takes into account the rating of protective device that protects the
circuit or part that needs to be protectively earthed.  If a part that could
fail to earth is protected by a 1A fuse then the protective conducter is sized
to pass the following test, otherwise a great many PCB tracks that carry earth
within a small SMPSU would be disallowed.

If a series connected mains socket or device is protected by a (say) 5A fuse
the intermediate bonding conductors to the equipment mounted socket outlet
could be reduced in size accordingly.  Fifteen years ago you couldn't do this,
but you can now.

This is the test for bonding conductors.
=================
The test current,duration of the test and test results are as follows:
- if the current rating of the circuit under test is 16 A or less, the test
current is 1,5 times the
current rating of the circuit under test, the current is applied for 60 s and
the resistance of
the PROTECTIVE BONDING CONDUCTOR , calculated from the voltage drop,shall not
exceed
0,1 ?;
=================

There are many cases where AS3100 or AS3108 say a specific thing cannot be done
but a more modern product specific standard may allow it, and AS/NZS3000 is no
longer a prescriptive standard with regard to anything on the equipment side of
the supply interface.

The damn standards change so often it costs us thousands of dollars a year to
keep up to date.




Re: Tingles from DVD players



"David, the pedantic FUCKWIT one.
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 ** " No reliance "  =  NO connection to the AC supply earth system.


WAKE  UP  FUCKHEAD:

AS/NZ  standards are for engineers and installers to heed.

The issue here relates to  *ordinary consumers*   !!!

Consumers are neither aware of nor need to follow published standards.

The law of  **negligence** certainly applies to them though.




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** Blah,  blah,  blah  -    same as I said.

     Piss off  -    you damn  IDIOT.



......  Phil



Re: Tingles from DVD players



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Shouldn't that read "David.......... won" ?

Phil lost....


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Re: Tingles from DVD players



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Thanks, that was quite interesting.  Thanks also to the other posters,

I wish that standards like these which have to all intents and purposes
become legally binding, were automatically placed in the public domain.
Imagine if all laws were as difficult to access - the public would not
tolerate that.
Chris

Re: Tingles from DVD players



"Chris Jones"
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 ** It was a whole load of irrelevant shit.


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** Only binding on industry and even then only in a few cases.


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** Very bad idea.

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** Until the internet arrived laws  ( ie legislation) WAS difficult to
access .

The public tolerated it just fine for centuries.

Even now, only a tiny few( other than law students & lawyers) ever bother to
access the info.

Most of it is FAR to complicated and confusing to the novice.




........ Phil



Re: Tingles from DVD players


On Fri, 24 Mar 2006 23:44:35 +0000, Chris Jones
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I agree.

An advantage of Electrical Registration in NZ is that the Electrical
Workers Registration Board supply free of charge paper copies of the
Electricity Regulations, AS/NZS 3000, AS/NZS 3760, and pdfs on a cd of
9 others to registered workers.

Last year they announced an agreement with Standards NZ to give online
access for registered workers to all standards referenced in AS/NZS
3000. Unfortunately that hasn't yet occured because there are problems
between the two organisations websites.

--
Regards
Malcolm
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Re: Tingles from DVD players



"Malcolm Moore"
 Chris Jones
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** LOL

Same way sheep agree  !!


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** AS/NZS 3000  =  Electrical installations (known as the Australian/New
Zealand Wiring Rules)

    AS/NZS 3760  =  In-service safety inspection and testing of electrical
equipment.


A complete fool ( like this Malcolm cretin for example) can read the above
cover to cover as many times as he likes and still wind up not having a
DAMN  CLUE about real world electrical safety.


Baaaaaaaahhhhhhhhhhh.....




........  Phil







Re: Tingles from DVD players


On Mon, 27 Mar 2006 11:08:49 +1100, "Phil Allison"

<snipped insults>

One think i found when getting gear approved in QLD is that the
inspector was less aware of the Standards than I was. What is even
worse is that he granted an approval on a product that was quite
clearly not compliant. I can handle this for a small time production
that will never face the public, but the device in question I can
guarantee that a significant amount of QLD/VIC public have been
exposed too. Fortunately the 'Approved product' was fixed before
shipping.

I find it obscure that EMC compliance is more difficult and expensive
than electrical compliance. Go figure..



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Re: Tingles from DVD players


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With many items fitting into the non-decalared categories
it is common to find that many (and I mean a lot) do not
meet essential safety requirements.  The inspectors have
litle or no idea about such equipment unless they have a
lab report in hand.  For instance the NSW DFT has a zero
budget allocation for testing such equipment to see if it
is safe.  I wish I was joking when I said they won't do
anything unless someone is injured or killed, or unless
a third party (competitor) funds the initial compliance
checking activity.  The legislation is there, but no money
to proactively enforce it.

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Depends on the device, what has to be done and who
you go to.  Some safety tests can be done with a multimeter
but it is unlikely that a proper EMC test could be done
without the proper equipment.  Hence the cost
differential for simple products.



Re: Tingles from DVD players


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And that would be a problem how?
 
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says you...  

what's the deal with laplink cables ?

and connecting what's that bad thing that going to happen by connecting my
VCR and DVD player to my ancient TV (Phillips K9ii) which has an eathed
antenna connector.  and my junk CD player (CD-rom drive in an old  apple
external 5.25" enclosure with RCA sockets on the back) (earthed) is connected
to my cheap sterio.

--

Bye.
   Jasen

Re: Tingles from DVD players


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 If the connector shells at each end are connected together, they
can connect the frame earth of the two devices. Not always a good
thing.

G
--
 "Men will never be free until the last king is strangled with the
  entrails of the last priest." (Diderot, paraphrasing Meslier)

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