Double Insulated - safe?

[anon]

I recently had to repair a stereo amp/receiver (big name brand,
approx 7 years old). I was dismayed to find exposed solder tags,
bare pcb wire links etc carrying mains voltages.

I thought the practice of having exposed mains voltages inside
equipment was history. In my 25 years of servicing professional
instrumentation (many brands) it was extremely rare to see
exposed mains under the hood. But alas consumer electronics
don't seem to care.

More disturbing is that the above amp/receiver is not earthed
and displays the double insulated logo (two concentric squares).
So where's the so-called "double insulation" ?

As I recall, double insulation standards was supposed to mean
equipment had two levels of insulation - functional insulation
(e.g. the plastic coating on wires) and protective insulation (e.g.
a physical barrier between mains and secondary wiring). The
idea being that even under catastrophic failure, the user would
still be safe.

In the amp/receiver in question, no attempt was made to separate
the mains parts from the secondary wiring. All it would require is
for a mains wire connected to one of the exposed solder tags to
fall off and touch the nearby metal case and it becomes potentially
lethal.

If this is what electrical safety standards have now degenerated
to then I'm totally appalled.

 

[Phil Allison]

"anon"

I recently had to repair a stereo amp/receiver (big name brand,
approx 7 years old). I was dismayed to find exposed solder tags,
bare pcb wire links etc carrying mains voltages.

** Very common in all sorts of equipment - service people have to be wary
and use an ELCB.

More disturbing is that the above amp/receiver is not earthed
and displays the double insulated logo (two concentric squares).
So where's the so-called "double insulation" ?

** The correct name is "class 2" .

The term "double insulation" is not a literal description.

As I recall, double insulation standards was supposed to mean
equipment had two levels of insulation - functional insulation
(e.g. the plastic coating on wires) and protective insulation (e.g.
a physical barrier between mains and secondary wiring). The
idea being that even under catastrophic failure, the user would
still be safe.

** For an appliance to meet "class 2" requirements there are many rules to
follow.

The most important ones relate to the AC supply transformer which must be so
constructed that no likely overload or failure can bring the primary and
secondary into contact. Often this requirement can be met by adding a
thermal fuse to the primary so that power is shut off if ever the temp
becomes unsafe.

Usually , there is also fire proof and other high temp insulation fitted
between the primary and secondary windings.

In the amp/receiver in question, no attempt was made to separate
the mains parts from the secondary wiring.

** How much separation do you expect ???

I bet there were at least two layers of plastic in every case.

All it would require is
for a mains wire connected to one of the exposed solder tags to
fall off and touch the nearby metal case and it becomes potentially
lethal.

** Bet the wire ends are looped through solder tags prior to soldering.

Where an item is not likely to be subjected to high levels of vibration -
sleeving every cable termination is hardly essential.

If this is what electrical safety standards have now degenerated
to then I'm totally appalled.

** The fact is, the item you are whingeing about is not a "prescribed item"
so does not have to be inspected and approved by a registered lab before
going on sale.

The double square symbol is simply applied in the (Asian ?) factory as
evidence that "class 2" rules have been followed and the user need to be
informed the device should not be earthed.




......... Phil

 

[David, not to be confused]

As I recall, double insulation standards was supposed to mean
equipment had two levels of insulation - functional insulation
(e.g. the plastic coating on wires) and protective insulation (e.g.
a physical barrier between mains and secondary wiring). The
idea being that even under catastrophic failure, the user would
still be safe.

This is still principle, but now (say the last fifteen years) there is also
reinforced
insulation. That is one, homogenious (sp?) system that is equivalent to the
protection afforded by basic + supplementary insulation (double insulation).

** How much separation do you expect ???
I bet there were at least two layers of plastic in every case.

A 6.0 mm air gap is all that is required to separate from the 240V mains. Not
much is it,
but as Phil pointed out, if there isn't any vibration, movement or
contamination
then a hazard won't suddenly appear.

There is no requirement for protection of service personel unless access is via
a
hazardous area. Compare reaching into the bowels of a photocopier as opposed
to taking
the lid off the amplifier. A trained service person is supposed to be able to
identify, either
visually, or by measurement, areas which are safe enough to handle. Guarding is
not
required if hazards are reasonably identifiable.

 

[Dand]

"anon" <invalid@nospam.com> wrote in message
news:4376aadb_1@news.chariot.net.au...

I recently had to repair a stereo amp/receiver (big name brand,
approx 7 years old). I was dismayed to find exposed solder tags,
bare pcb wire links etc carrying mains voltages.

I thought the practice of having exposed mains voltages inside
equipment was history. In my 25 years of servicing professional
instrumentation (many brands) it was extremely rare to see
exposed mains under the hood. But alas consumer electronics
don't seem to care.

I think you are mistaken about what double insulation can mean now.
If the PCB board is insulted to the case by plastic stands, this is the
first insulation. Then the second is the case.
So a TV can have live mains on the PCB with only the case stopping people
touching it because its double insulated. You will see this is practically
everything now.

 

[Phil Allison]

"Dand"

I think you are mistaken about what double insulation can mean now.
If the PCB board is insulted to the case by plastic stands, this is the
first insulation. Then the second is the case.

** Shame when the "case" is the metal box of a piece of hi-fi or video gear.

BTW

What rock did you crawl out from under ?



.......... Phil

 

[FruitLoop]

"Phil Allison" <philallison@tpg.com.au> wrote in message
news:3ttmodFuco3iU1@individual.net...

"Dand"

I think you are mistaken about what double insulation can mean now.
If the PCB board is insulted to the case by plastic stands, this is the
first insulation. Then the second is the case.


** Shame when the "case" is the metal box of a piece of hi-fi or video
gear.

BTW

What rock did you crawl out from under ?

I thought you were a rock spider

......... Phil

 

[Phil Allison]

"FruitLoop"

I thought you were a rock spider

** No one here has any doubt that you are one.



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

 

[anon]

"Phil Allison" <philallison@tpg.com.au> wrote in message news:3tnpu2FriqcfU1@individual.net...

"anon"

I recently had to repair a stereo amp/receiver (big name brand,
approx 7 years old). I was dismayed to find exposed solder tags,
bare pcb wire links etc carrying mains voltages.

** Very common in all sorts of equipment - service people have to be wary
and use an ELCB.

Everyone has the right to safety whether it be user or repairer.
Other manufacturers have managed to design equipment without
exposed mains, why not consumer goods?

In the amp/receiver in question, no attempt was made to separate
the mains parts from the secondary wiring.

** How much separation do you expect ???

Last time I looked at the Australian Standard (circa 1980) it required
segregation of mains and secondary wiring so that overheating or fire
wouldn't result in them coming into contact.

I bet there were at least two layers of plastic in every case.

No. As I have indicated - numerous points of exposed mains (solder
tags, pcb links and pcb copper) with nothing to separate them from
the metal casing or secondary wiring other than air.

** The fact is, the item you are whingeing about is not a "prescribed item"
so does not have to be inspected and approved by a registered lab before
going on sale.

AFAIK all electrical goods sold in Australia are subject to the relevant
Australian safety standards, irrespective of whether formal testing or
approval was required.


If anyone has any further information or encountered similar situations
with so-called "double-insulated" equipment, I'd be interested to hear.

 

[anon]

"Dand" <dand@dand.net.au> wrote in message news:4379a345$0$25857$afc38c87@news.optusnet.com.au...

...

I think you are mistaken about what double insulation can mean now.
If the PCB board is insulted to the case by plastic stands, this is the
first insulation. Then the second is the case.
So a TV can have live mains on the PCB with only the case stopping people
touching it because its double insulated. You will see this is practically
everything now.

If the case was metal and the user could touch it then there'd be only
one level of insulation (the situation in the equipment I described).

 

[Phil Allison]

"anon"

"Phil Allison"

I recently had to repair a stereo amp/receiver (big name brand,
approx 7 years old). I was dismayed to find exposed solder tags,
bare pcb wire links etc carrying mains voltages.

** Very common in all sorts of equipment - service people have to be wary
and use an ELCB.

Everyone has the right to safety whether it be user or repairer.

** Blah blah - yawn......

Other manufacturers have managed to design equipment without
exposed mains, why not consumer goods?

** Pro gear is FULL of exposed bloody mains - you goose.

In the amp/receiver in question, no attempt was made to separate
the mains parts from the secondary wiring.

I bet there were at least two layers of plastic in every case.

No. As I have indicated - numerous points of exposed mains (solder
tags, pcb links and pcb copper) with nothing to separate them from
the metal casing or secondary wiring other than air.

** Last time I looked, air was a damn good insulator.

** The fact is, the item you are whingeing about is not a "prescribed
item"
so does not have to be inspected and approved by a registered lab before
going on sale.

AFAIK all electrical goods sold in Australia are subject to the relevant
Australian safety standards, irrespective of whether formal testing or
approval was required.

** AFAIK, that amp DOES comply.

BTW

I object strongly to the way you edited and selectively replied to my post
out of context in each case.




........ Phil

 

[FruitLoop]

"Phil Allison" <philallison@tpg.com.au> wrote in message
news:3tu7hrFubt7eU1@individual.net...

"FruitLoop"


I thought you were a rock spider


** No one here has any doubt that you are one.

Look in the mirror , thats if its not broken .

BTW since when did you constitute the whole NG , in your dreams ?

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

 

[anon]

"Phil Allison" <philallison@tpg.com.au> wrote in message news:3tveegFulkh1U1@individual.net...

"anon"
"Phil Allison"
...
I bet there were at least two layers of plastic in every case.

No. As I have indicated - numerous points of exposed mains (solder
tags, pcb links and pcb copper) with nothing to separate them from
the metal casing or secondary wiring other than air.


** Last time I looked, air was a damn good insulator.

How would this qualify as "double insulation" ?

...
BTW

I object strongly to the way you edited and selectively replied to my post
out of context in each case.

Anyone reading this thread would have seen your original response
in full. I disagree that anything said was "out of context".

 

[Phil Allison]

"anon"

"Phil Allison"

...
I bet there were at least two layers of plastic in every case.

No. As I have indicated - numerous points of exposed mains (solder
tags, pcb links and pcb copper) with nothing to separate them from
the metal casing or secondary wiring other than air.


** Last time I looked, air was a damn good insulator.

How would this qualify as "double insulation" ?

** Read my earlier post re " class 2 ".

BTW

I object strongly to the way you edited and selectively replied to my
post
out of context in each case.

Anyone reading this thread would have seen your original response
in full. I disagree that anything said was "out of context".

** All of it was.

You are a pompous dope.


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

 

[Jasen Betts]

On 2005-11-15, Phil Allison <philallison@tpg.com.au> wrote:

"Dand"

I think you are mistaken about what double insulation can mean now.
If the PCB board is insulted to the case by plastic stands, this is the
first insulation. Then the second is the case.

** Shame when the "case" is the metal box of a piece of hi-fi or video gear.

No layer of plastic lining the case under the pcb?

Bye.
Jasen

 

[Dand]

"anon" <invalid@nospam.com> wrote in message
news:437a8126$1_4@news.chariot.net.au...

"Dand" <dand@dand.net.au> wrote in message
news:4379a345$0$25857$afc38c87@news.optusnet.com.au...

...

I think you are mistaken about what double insulation can mean now.
If the PCB board is insulted to the case by plastic stands, this is the
first insulation. Then the second is the case.
So a TV can have live mains on the PCB with only the case stopping people
touching it because its double insulated. You will see this is
practically
everything now.

If the case was metal and the user could touch it then there'd be only
one level of insulation (the situation in the equipment I described).

There is nothing that says the outer insulation has to be non conductive,
just isolated.

 

[Phil Allison]

"Dand"

There is nothing that says the outer insulation has to be non conductive,

** Well dang me - I sure never heard 'bout this new fangl'd *conductive*
insulation before.




.......... Phil

 

[Phil Allison]

"Jasen Betts"
Phil Allison

"Dand"

I think you are mistaken about what double insulation can mean now.
If the PCB board is insulted to the case by plastic stands, this is the
first insulation. Then the second is the case.

** Shame when the "case" is the metal box of a piece of hi-if or video
gear.


No layer of plastic lining the case under the pcb?

** Why ?

The collect the poop when the board shits itself ?



.......... Phil

 

[anon]

"David, not to be confused with the other Davids." <dave@mailswap.telstra.com> wrote in message
news:2kdef.17875$Hj2.8808@news-server.bigpond.net.au...

As I recall, double insulation standards was supposed to mean
equipment had two levels of insulation - functional insulation
(e.g. the plastic coating on wires) and protective insulation (e.g.
a physical barrier between mains and secondary wiring). The
idea being that even under catastrophic failure, the user would
still be safe.

This is still principle, but now (say the last fifteen years) there is also
reinforced
insulation. That is one, homogenious (sp?) system that is equivalent to the
protection afforded by basic + supplementary insulation (double insulation).


** How much separation do you expect ???
I bet there were at least two layers of plastic in every case.

A 6.0 mm air gap is all that is required to separate from the 240V mains. Not
much is it, but as Phil pointed out, if there isn't any vibration, movement or
contamination then a hazard won't suddenly appear.

If the standard specifies a minimum gap then it would need to be maintained
even under adverse conditions. That would mean either a physical barrier,
cable clamps etc to prevent movement.

BTW the equipment in question doesn't have even that separation - the two
mains wires (blue, brown) are lying over other secondary wiring and adjacent
to the transformer frame.

There is no requirement for protection of service personel unless access is via
a hazardous area. Compare reaching into the bowels of a photocopier as opposed
to taking
the lid off the amplifier. A trained service person is supposed to be able to
identify, either
visually, or by measurement, areas which are safe enough to handle. Guarding is
not
required if hazards are reasonably identifiable.

Even for "trained personel" working inside equipment where harazards
exist but are not identified or be easily identifiable could be considered
unreasonable.

Most (if not all) electronics service personel have received an electric
shock at least once in their career. Luckily most are not fatal - but could
have been. Would you consider such a state of affairs "reasonable" ?

Safety laws don't specify what's "reasonable" so such things ultimately
have to be tested in court. Suffice to say, I wouldn't like to be an
employer, manufacturer or serviceman trying to defend a charge of
negligence.

The stereo receiver in question has no points identified as being mains,
nor are there any hazard warnings inside or out.

 

[anon]

"Phil Allison" <philallison@tpg.com.au> wrote in message news:3tvoebFunlekU1@individual.net...

"anon"
"Phil Allison"

...
I bet there were at least two layers of plastic in every case.

No. As I have indicated - numerous points of exposed mains (solder
tags, pcb links and pcb copper) with nothing to separate them from
the metal casing or secondary wiring other than air.


** Last time I looked, air was a damn good insulator.

How would this qualify as "double insulation" ?


** Read my earlier post re " class 2 ".

Nothing applicable there.

Look up a few references on the internet for an understanding
of what constitutes insulation for the purposes double-insulated
aka "class 2" equipment.

 

[Phil Allison]

"anon"

BTW the equipment in question doesn't have even that separation - the two
mains wires (blue, brown) are lying over other secondary wiring and
adjacent
to the transformer frame.

** An air gap is specified where there is no insulation - ie PCB tracks
carrying AC mains need to be separated from other tracks by a gap.

Usually, internal AC leads are sleeved in clear plastic where they may
contact metal parts - but this is not essential if the wires are coated in
a plastic of a sufficient thickness.

Even for "trained personel" working inside equipment where harazards
exist but are not identified or be easily identifiable could be considered
unreasonable.

** Yawn - blah blah blah .

You are clutching at straws.

Safety laws don't specify what's "reasonable" so such things ultimately
have to be tested in court. Suffice to say, I wouldn't like to be an
employer, manufacturer or serviceman trying to defend a charge of
negligence.

** Tiny straws.

The stereo receiver in question has no points identified as being mains,
nor are there any hazard warnings inside or out.

** There is no hazard to warn a user about. The internal parts that are
live in use are bleeding obvious to any tech qualified to work on mains gear
when it is powered up.

You are clutching at straws - tiny ones.



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