Double Insulated - safe?

"anon"

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

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.

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

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

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

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).

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.

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.

"Dand"

BTW

What rock did you crawl out from under ?

......... Phil

gear.

I thought you were a rock spider

"FruitLoop"

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

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?

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.

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.

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.

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).

"anon"

BTW

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

....... Phil

Look in the mirror , thats if its not broken .

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

How would this qualify as "double insulation" ?

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

"anon"

You are a pompous dope.

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

No layer of plastic lining the case under the pcb?

Bye. Jasen

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

"Dand"

......... Phil

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.

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.

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.

"anon"

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.

You are clutching at straws.

You are clutching at straws - tiny ones.

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

"anon" "Phil Allison"

Quote:

" The correct name is "class 2" . The term "double insulation" is not a literal description. "

Try reading a copy of the Australian Standard ( AS3100) that describes Class 2 and "double insulation".

.......... Phil