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Hi Doug:
> Take a look at IEC 60664-3: 2003-02 "Insulation coordination for
> equipment with in low-voltage systems - Part 3: Use of coating, potting
> or moulding for protection against pollution."
>
> This standard covers the topic very well and is referenced by IEC
> 61010-1: 2nd Ed. 2001-02. ...
>
> You will find that there are two types of coatings recognized by IEC
> 60664-3. One type simply provides pollution degree reduction and the
> other is considered solid insulation. ...
Thank you for the citation.
I don't believe I contradicted IEC 60664-3.
However, now that you pointed it out, I find
I have difficulty agreeing with Sub-clause
4.4, which specifies minimum dimensions
between conductors that are either:
- surface of a PWB covered by a coating,
or
- inner layer conductors
where the coating or prepreg fully excludes
air and is therefore a solid insulation.
The Sub-clause requires minimum distances
through insulation where a joint is involved.
On the other hand, if the insulation was a
single, homogeneous piece, then there would
be no minimum distance through insulation.
Each different solid insulation material has
its own electric strength, kV/mm. This is a
material property.
If a joint has no air, and the two solid
insulations are contiguous, then the distance
through insulation should be according to
the material with the least electric strength
value, kV/mm.
Instead, Sub-clause 4.4 specifies the kV/mm
without regard for the material properties.
This does not seem to me to be consistent
with physical principles. What am I missing?
Best regards,
Rich
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