On 1/8/13 3:08 AM, "Richard Nute" <[email protected]> wrote:
>
>
> Hi Scott:
>
>
>>
>>> Class II products have two levels of insulation: basic and supplementary
>>> insulations. Each insulation is safe to prevent from electrical shock in
>>> normal use. Why does a product need two levels of insulation in its
>>> lifespan? How often is a second insulation being used?
>>>
>>
> Basic insulation is a safeguard against electric shock under normal
> conditions.
>
> Supplemental insulation is a safeguard against electric shock under fault of
> basic insulation.
>
> Basic and supplemental insulations are chosen that what deteriorates one will
> not deteriorate the other.
>
> The probability of failure of two insulations is multiplication of two very
> small probabilities which is a very very small probability.
>
> Today's insulations are very good and not likely to fail throughout the
> lifetime of the equipment. This wasn't always the case.
>
> Scott: If the possibility is so small, is it worthwhile to recall the products
> that one insulation deteriorates? Stopping sale is a must.
>>
>>> Nine out ten people do not know the meaning of class II symbol. What is
>>> main purpose to have a double square symbol on class II products?
>>>
>>
> The double square symbol means class II as opposed to class 0 (which is
> two-wire without double insulation). Only design
> and test people need to know the meaning of the class II symbol.
>
> Scott: Those professionals, design and test people are relying on the symbol
> to determine the safety protection class?
>
> Hope this helps.
> Rich
>
>
>
-
----------------------------------------------------------------
This message is from the IEEE Product Safety Engineering Society emc-pstc
discussion list. To post a message to the list, send your e-mail to
<[email protected]>
All emc-pstc postings are archived and searchable on the web at:
http://www.ieee-pses.org/emc-pstc.html
Attachments are not permitted but the IEEE PSES Online Communities site at
http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used
formats), large files, etc.
Website: http://www.ieee-pses.org/
Instructions: http://listserv.ieee.org/request/user-guide.html
List rules: http://www.ieee-pses.org/listrules.html
For help, send mail to the list administrators:
Scott Douglas <[email protected]>
Mike Cantwell <[email protected]>
For policy questions, send mail to:
Jim Bacher: <[email protected]>
David Heald: <[email protected]>
