Tingles from DVD players

[Russ_Verdon]

Hi, I just did a round of "kerbside shopping" and picked up 2x Digitor DVD
players from the same place. They both work. The only thing I can think is
that they give you a small shock between their chassis and power earth. I
can only surmise that the owner thought they were faulty and ditched them as
a result. I have picked up another DVD player in similar circunstances,
going, but tingling.
I believe the shock would be some capacitive coupling to their chassis from
the switchmode PS. I can measure 105 volts AC from their chassis to earth,
but no current .
Is there any rule that stops you earthing these devices, given that the
connection via the signal leads to an earthed amp etc would probably do this
anyway?
Do the manufacturers expect all devices to be turned off so that customers
don't experience shocks when changing leads around? If chassis earthing
elminates this issue, then it would be a nice feature and customer friendly
to do so. I guess the amount of copper / star washer etc saved per unit for
them outweighs thoughts for the customer.
Any comments?

Russell

 

[Phil Allison]

"Russ_Verdon"

Hi, I just did a round of "kerbside shopping" and picked up 2x Digitor
DVD
players from the same place. They both work. The only thing I can think is
that they give you a small shock between their chassis and power earth. I
can only surmise that the owner thought they were faulty and ditched them
as
a result. I have picked up another DVD player in similar circunstances,
going, but tingling.
I believe the shock would be some capacitive coupling to their chassis
from
the switchmode PS. I can measure 105 volts AC from their chassis to earth,
but no current .
Is there any rule that stops you earthing these devices, given that the
connection via the signal leads to an earthed amp etc would probably do
this
anyway?

** Yes - the units are not longer "double insulated" or of "class 2"
construction if you substitute a 3 core lead.

Do the manufacturers expect all devices to be turned off so that customers
don't experience shocks when changing leads around?

** Only a few folk feel any tingle at all.

If chassis earthing
elminates this issue, then it would be a nice feature and customer
friendly
to do so.

** Completely silly.

The use of Class 2 construction is a VERY deliberate decision and for very
good reasons.

I guess the amount of copper / star washer etc saved per unit for
them outweighs thoughts for the customer.

** Absolute crapology.

Any comments?

** You seriously temp me.

Never heard of earth loop hum ?????




.......... Phil

 

[Phil Allison]

"Chris Jones"

Sure, that seems obvious.

** You have completely missed the point.

The device would then be modified, the original
electrical approval would not be valid,

** Correct - so the markings on the unit (ie "class 2" and the double
square symbols) would be then ILLEGAL.

and it would not be possible to
approve the device as a class 2 device with the case earthed. Are you
aware of any technical reason why the device could not be approved as a
class 1 device (hypothetically, since the cost of testing would be more
than prohibitive)?

** Yawn.

This is an entirely separate issue to the OP's question AND my reply.

Apart from the earth loop hum you refer to, what reasons are you referring
to?

** 1. Class 2 construction is far SAFER for the user.

2. Class 2 construction meets world wide electrical approvals making it far
easier for makers to market the same design world wide.

3. The use of class 2 is almost universal for some classes of electronic
equipment.

4. There is a PROHIBITION on interconnecting class 1 and class 2 equipment.





......... Phil

 

[Phil Allison]

like a laplink cable?

** Piss off - kiwi tenth wit.

The sheep are missing you.





........ Phil

 

[Phil Allison]

"Chris Jones"



** Do you constantly move the goalposts at sporting events too ?





........... Phil

 

[Phil Allison]

"Chris Jones"

I am surprised by (4)

** Have you never seen the words " Double Insulated - Do Not Earth " on
the back of a class 2 item ??

Pretty clear isn't it?

since many hi-fi amplifiers (at least older ones) do
have an earthed case, for better or for worse. It is not made very clear
to the average user that connecting the amplifier to a typical (class 2)
CD
player would be prohibited,

** It is not prohibited by criminal law - so no police officer will arrest
you for doing it.

But it is an * unsafe practice* that could be considered as " serious
negligence " by a court if a person were injured or killed.

for example I haven't seen such a warning in
the instruction manual of a CD player.

** " Double Insulated - Do Not Earth " on the back of the player is a
*stronger warning* that anything printed in a user manual that likely gets
lost with the packaging.

Equipment makers are not liable for what users may WRONGLY do when
interconnecting items of gear - so just ignore the issue.

The matter is very much an *X rated topic * in the home entertainment
electronics industry.

I don't have the necessary
knowledge of the standards to refute what you say, but it does surprise
me.

** Imagine a hi-fi system with every item in it class 2 - so there is no AC
ground to the metalwork.

Next, an item is added to the system, ie a nice old valve tuner just bought
from Ebay but with no AC plug.

Next, the user inadvertently wires up the new plug wrongly with active and
earth reversed and makes all the connections.

The hi-fi system will still work just as before ( but not the tuner) but
with ALL the metalwork, connecting leads and even the loud speakers now
LIVE !!!

In countries with 240 volt AC power, this is a FATAL accident scenario
!!!!


NOTE:

One of the BIGGEST user safety advantages of class 2 construction is that
no matter how WRONGLY the AC plug is wired & no matter what is wrong with
the AC outlet, you cannot get active onto the earth of the gear.




......... Phil

 

[Phil Allison]

"Terry Given"

a major advantage of class 2 is that its cheaper.

** Bullshit it is.

The specs for the AC supply transformer alone are way beyond that for class
1.

The design rules for every part of the AC side are way tougher.

the plug, cable and interconnects cost less,

** By a few cents only.

and because of the double insulation, none of the metalwork has to be
earthed, which it does with class 1 - for many standards the metalwork
earthing must carry the rated current, further increasing the cost.

** What absolute drivel.

The above scenario can only happen when people fiddle with things,

** More " Pinball Wizard " bullshit.

so is not relevant to manufacturers (they build them right).

** It is *very elevata" to the increased safety of class 2.

It is *very relevant" to the PROHIBITION on earthing a class 2 appliance.

Such a scenario also occurs with a single class 1 appliance wired up by
the same dickhead.

** But NOT a system of interconnected class 1 appliances.

Hence the prohibition on earthing a class 2 appliance or system thereof.

They are very safe until you do that.

Voila, live chassis (and dead operator).

** Please go try it now.




........ Phil

 

[Phil Allison]

"The Pinball Wizard of Nelson "

double insulation pretty much means 2 sets of insulation,

** Absolute bullshit.

so that when one fails there is still one left.

** Absolute bullshit.

yes the xfmr is a bit more expensive,

** Much more - the cheapest construction methods are outlawed.

The popular and cheap toroidal is basically outlawed.

but a whole bunch of other stuff gets cheaper.

** Absolute bullshit.

look inside a hair

** The subject is DVD players and the like - fuckhead.

not really,

** Get stuffed - Kiwi LIAR !!




........ Phil

 

[Phil Allison]

"The Pinball Wizard of Nelson "

ROTFLMAO!

** Go **** yourself - you useless Kiwi ARSEHOLE .

first, lets un-snip what I posted:

"double insulation pretty much means 2 sets of insulation, so that when
one fails there is still one left"

** No.

The term "double insulation" is the popular name for "class 2" construction
= a whole set of technical design rules and restricted materials approvals
that make it * SAFE * to use and sell an appliance that has no connection
to the supply earth as a means of preventing electric shock hazard to users.

All way over this Kiwi fuckwit's pointy head.

In other words, exactly what I said.

** Wrong context - Kiwi ARSEHOLE.

pah. look at those sorts of xfmrs, its not very complex.

** Learn to read - you dumb Kiwi ARSEHOLE.

on what basis?

** Go read AS3108 some day - ARSEHOLE.

Then figure why toroidals are extremely rare in class 2 gear, consumer or
otherwise.




........ Phil

 

[Malcolm Moore]

"Chris Jones"



** Have you never seen the words " Double Insulated - Do Not Earth " on
the back of a class 2 item ??

Pretty clear isn't it?

I've just checked all the double insulated items in my home and NONE
of them carry a warning such as you describe. It would be useful to
know how general such a warning is. I suggest everyone reading this
thread check their equipment and report back their findings. My
equipment includes items from NEC, Philips, Sony, Teac, Mitsubishi,
Sanyo & Microsoft.

snip

Equipment makers are not liable for what users may WRONGLY do when
interconnecting items of gear - so just ignore the issue.



The matter is very much an *X rated topic * in the home entertainment
electronics industry.

So where does the "PROHIBITION" come from?
Previously you said such interconnection was prohibited, now you're
saying to ignore the issue??

** Imagine a hi-fi system with every item in it class 2 - so there is no AC
ground to the metalwork.

Next, an item is added to the system, ie a nice old valve tuner just bought
from Ebay but with no AC plug.

Next, the user inadvertently wires up the new plug wrongly with active and
earth reversed and makes all the connections.

The hi-fi system will still work just as before ( but not the tuner) but
with ALL the metalwork, connecting leads and even the loud speakers now
LIVE !!!

In countries with 240 volt AC power, this is a FATAL accident scenario
!!!!

If this danger was significant then the use of Class 2 equipment is
inherently unsafe because it would be relying on user action to make
it safe, the user action being to not interconnect with other commonly
available items. As you say above, "Equipment makers are not liable
for what users may WRONGLY do.....", but regulators are always
interested in such things. They seem relaxed about the situation.

snip

 

[Phil Allison]

"Chris Jones"

I don't consider posting to usenet to be a competition,

** Then why keep moving the goal posts like is is one you cannot bear to
loose ??

I just like to learn stuff.

** If you mean that, then why make it impossible for anyone to answer you ?




......... Phil

 

[Phil Allison]

"Malcolm Moore"
"Phil Allison"

I've just checked all the double insulated items in my home and NONE
of them carry a warning such as you describe.

** The warning notice is not compulsory.

Only the use of the "double square" symbol or the words "Double Insulated"
are.

The matter is very much an *X rated topic * in the home entertainment

So where does the "PROHIBITION" come from?

** The fact that a class 2 appliance must not be earthed.

Previously you said such interconnection was prohibited, now you're
saying to ignore the issue??

** Huh ???

What madman's logic is this ?

What the hell do you think "X -rated " means ???

If this danger was significant then the use of Class 2 equipment is
inherently unsafe because it would be relying on user action to make
it safe, the user action being to not interconnect with other commonly
available items.

** Absolute drivel.

Class 2 construction appliances are inherently much safer than class 1
types.

What users do that COMPROMISES that additional safety is beyond the control
of makers or authorities.

As you say above, "Equipment makers are not liable
for what users may WRONGLY do.....", but regulators are always
interested in such things. They seem relaxed about the situation.

** SFA they can do about it.

The issue is one of legal liability on the part of someone who elects to
earth a class 2 item.



......... Phil

 

[Phil Allison]

"Chris Jones"

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.

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

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),

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

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 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.

The root cause of the problem is of course having someone who thinks they
can wire a plug but cannot.

** Millions of them around.

Heaps of places sell 3 pin plugs to the public.

The problem is they might not be the one to
get killed, it'll be the neighbour's kid or something like that.

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

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.

** 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

 

[David, not to be confused with the other Davids.]

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

Hi, I just did a round of "kerbside shopping" and picked up 2x Digitor DVD
players from the same place. They both work. The only thing I can think is
that they give you a small shock between their chassis and power earth. I
can only surmise that the owner thought they were faulty and ditched them as
a result. I have picked up another DVD player in similar circunstances,
going, but tingling.

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.

Is there any rule that stops you earthing these devices, given that the
connection via the signal leads to an earthed amp etc would probably
do this anyway?

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.

Do the manufacturers expect all devices to be turned off so that customers
don't experience shocks when changing leads around? If chassis earthing
elminates this issue, then it would be a nice feature and customer friendly
to do so. I guess the amount of copper / star washer etc saved per unit for
them outweighs thoughts for the customer.
Any comments?

Russell

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

 

[Phil Allison]

"David, not to be confused with the other Davids."

There is no rule in the safety or wiring standards that prevents you from
doing so,

** Of course there is !!

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

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.

** There is.

A Class 2 appliance must not be earthed.

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).

** 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)

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.

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

( snip more irrelevant drivel )

4. Class 2 construction does not mean double insulation.

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




........ Phil

 

[Phil Allison]

"Terry Given"

the prohibition on earthing class 2 appliances does not relate to
consumers plugging them into class 1 appliances,

** Yawn .......

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




........ Phil

 

[David, not to be confused with the other Davids.]

** Of course there is !!

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

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

** 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)

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.

 

[David, not to be confused with the other Davids.]

are you aware of any triple-insulated foils?

I haven't seen any (yet) that aren't of wrapped and folded insulation lay-up.

The mandrel test for flexibility and adherence would pretty much exclude the
use of other than round cross-sections in order to pass the 6 kV dielectric
strength test (based on my experience to date, the edge of the foil would
damage the layer(s) of extruded or spiral wrpped insulation).

Now I have said this, I will probably see one tomorrow

High current devices using foil windings usually have very bulky concentric
windings, since the insulation layup for each layer is sometimes as thick or
thicker than the foil. Must be a right bugger to make them to even
semi-precise tolerances.

 

[Phil Allison]

"David, the pedantic FUCKWIT one.

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.

** " 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.

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

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

Piss off - you damn IDIOT.



....... Phil

 

[Phil Allison]

"Terry Given"

= Kiwi ARSEHOLE & MASSIVE BUCKET

" David, the pedantic FUCKWIT one."

good stuff on the standards.

** Yawn - none of it had ANY relevance at all.

There's not much point replying to Phil, he's wrong and being abusive
because you proved it quite conclusively.

** WAKE UP - YOU ASININE FUCKHEADS:

AS/NZ standards are ONLY for engineers, manufacturers and installers to
heed !!

The potential shock hazard issue with class 2 and class items mixed in a
home entertainment system is all about what *ordinary consumers* do - at
home !!

Ordinary consumers are NOT aware of nor need to consider published standards
AT ALL !!

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

Shame they does not apply to ANONYMOUS idiots posting dangerous CRAPOLOGY !





......... Phil