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Safety of Electrical Equipment

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coates

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I remember watching an episode of Watchdog on TV where they were doing teardowns of fake phone chargers and remember one part where the "safety expert" was pointing out that the thickness of an insulated wire wasn't sufficient to pass standards. At the time I thought "OK it's thin but I bet it's rated to the correct voltage and it's inside the box so how likely is it going to cause a safety issue?"

My question is what standards is he talking about? Is there a table somewhere which says 300V insulated wiring needs to be at least x mm thick? As long as the wiring is rated correctly I don't see the problem.
 

KlausST

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Hi,

Region: many countries/regions have their own safety regulations.
Application: safety regulations also depend on application, like: commercial, industrial, aerospace, medical... but also: plastic case vs metal case ... and also: functional isolation (in the meaning to avoid arcing and fire) or protecting isolation (in the meaning to protect humans against electrical shock)
Environment: humidity, temperature, pollution..

It´s a wide range, thus there is no "general answer".

In your case: phone chargers: = Commercial product, indoor use, plastic case....
-> I assume the wire just needs single functional isolation. This usually is what you find on the wire´s datasheet.
Yes: every wire from every manufacturer comes with a datasheet. The manufacturer needs to provide it. (if he does not, then don´t use this wire)

Wire manufacturers will also provide additional informations. Look at their internet sites.

Klaus
 
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FvM

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I'm not motivated to review lengthy videos and the specific video isn't available any more, but general speaking there are applicable safety standards.

A phone charger must provide so-called reinforced insulation between main and low voltage circuits and pass tests with e.g. 2300 VAC between input and output.

The pattern of damage in the linked photo seems to show a blown wire between mains terminals and primary circuit, but the cause is not clear.

Apparently an electric arc jumped over to the secondary side. The event must not necessarily be raised by an inappropriate design. A lightning stroke hitting the landline near the house won't be covered by safety standards.

But it can be a design problem, e.g. a broken connection wire causing a short between primary and secondary. Safety standards require a reliable fixation to prevent similar accidents, probably more important than insulation thickness in this case, although there are requirements for it. A primary circuit wire capable of touching the secondary must have double insulation, just 300V rating isn't enough.
 

coates

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Safety standards require a reliable fixation to prevent similar accidents, probably more important than insulation thickness in this case, although there are requirements for it. A primary circuit wire capable of touching the secondary must have double insulation, just 300V rating isn't enough.

This is what I don't like. Safety standards open to interpretation. Who's going to tell me whether the fixation is reliable enough or not to use 300V wire?
 

marce

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They are not open to interpretation, you have to achieve the required standards and do so by design and testing... By use of the correct wire, the correct insulation and the correct spacing's between exposed metalwork.
 

coates

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For example, inside an enclosure you have mains voltage wiring and secondary voltage wiring. There will always be terminals, leads, pins, etc. at mains voltage that are uninsulated. Are you telling me that all the secondary voltage wiring must be rated to 600V just incase it miraculously bends itself inside the enclosure so that it touches the exposed terminals/leads/pins?
 

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Are you telling me that all the secondary voltage wiring must be rated to 600V just incase it miraculously bends itself inside the enclosure so that it touches the exposed terminals/leads/pins?
If you work on this field seriously, you want to review the respective safety standards yourself. We can just give a few hints.

You also get an idea by carefully inspecting devices designed by trustworthy manufacturers. You'll notice that mains wires inside an enclosures that are not clearly hindered from touching a low voltage circuit are either inside a cable or an additional insulation tube.
 

KlausST

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Hi,

Are you telling me that all the secondary voltage wiring must be rated to 600V just incase it miraculously bends itself inside the enclosure so that it touches the exposed terminals/leads/pins?
Nobody is telling this.
.. but in some cases the secondary wiring indeed needs to be rated for the higher voltage. .. it depends...

Klaus
 

coates

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Have you guys experienced this in your work? Have you had to seek out all the standards for your products, purchase every one of them, and read through them all carefully? Or have you just sent the product to some testing consultant and they tell you everything that's wrong with it?
 

KlausST

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Hi,

I´m designing industrial electronics equippment. Sometimes for high voltage >10.000 V AC and high current > 6.00A AC, regulated power >1MW.

I have to keep on the standards, otherwise I am personally responsible accidents.
And if you see the values above, then maybe you understand that an "accident" easily can cause fire and explosions and easily may kill humans.

Thus - Yes: I´ve bought these (expensive) standards. And did carefully read them. And made my own calculations, Excel sheets and so on... Yes, it takes time.

But - No: I didn´t buy all standards, just those that I need. There are selection guides to choose the right standard.

Klaus
 

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