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December 2005

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Subject:
From:
"Roach, David" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Roach, David
Date:
Thu, 1 Dec 2005 10:54:24 -0600
Content-Type:
text/plain
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text/plain (111 lines)
Phil, you might be able to get some sort of permanent conductive or static
dissipative coating applied to the plastic, maybe some type of a carbon
coating.  There are "chrome" plating processes for plastics, too, but I
don't know if they are real metal or if they are conductive.  I don't know
where to start on searching for a company to apply such a coating.  You
might check with plating and paint shops.  A computer manufacturer that I
used to work for had some type of conductive coating applied to the inside
of a plastic enclosure.  It looked like silver paint.  I don't know if this
was to reduce static voltage buildup or for EMI/RFI reduction, maybe both.

What is arcing in your device?  Is the high voltage component arcing to the
non-conductive enclosure?  I am certainly no expert on static charging and
discharging, but if the high voltage compenent is arcing to the enclosure,
you might have a bigger problem with a conductive (grounded) enclosure.  If
a static charge is building up on the enclosure and arcing to ground, having
a conductive enclosure might take care of the problem, though it might
increase the likelihood of the high voltage component arcing to the
enclosure.  If there is any significant current draining through the
enclosure after it is made conductive, this would probably indicate
insufficient dielectric strength (dielectric material and/or thickness)
between the high voltage components and the enclosure.  Have you calculated
the dielectric breakdown voltage for your application?  If the dielectric is
air (the most likely material, I would guess), you will have to look at the
dielectric strength of air at different humidity levels and temperatures.
Even if you specify a maximum operating humidity of something less than
100%, I think I would make sure there is more than sufficient dielectric
strength at 100% humidity, with some safety margin, probably a rather
generous safety margin when looking at high voltage arcing.

Dave Roach (Mechanical Engineer who knows just enough about electricity to
be dangerous)

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Nutting
Sent: Thursday, December 01, 2005 6:53 AM
To: [log in to unmask]
Subject: Re: [TN] Anti static sprays

Hmmmm... This is good information, but it is not relative to our
problem.

We have a high voltage generator in a molded plastic flame retardant
enclosure.  We are finding that with the material presently used there
appears to be static charging going on which is causing instability and
arcing in the unit.

Certainly changing the material on the enclosure is probably the best
long term solution.  The question is how can we improve the inventory we
have on hand so it is less prone to static charging.  It is not
practical to recoat the unit regularly.  I need to coat it once and have
it work for a very long time.

Phil

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of R Sedlak
Sent: Wednesday, November 30, 2005 6:02 PM
To: [log in to unmask]
Subject: Re: [TN] Anti static sprays

Best place to apply an anti-stat is always last step in process.

  Rudy Sedlak




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