Hi Eric,
Having been through this a while ago, I'll discuss what
I went through from memory. This information is now 2 years old.
The conductive coating is not a reliable ground. Primary ground
in the product on which I worked was on the switcher. Assembly
line testing hipotted with the regular line cord hookup and approvals
testing was done as with any other product. AS LONG AS I used the
conductive coating as shielding, I was in the clear. IOW, it didn't carry
any return currents from any circuits.
I'm also assuming that the coating is not user accessible.
It's inside the product. At least on my machine, user accessible
grounding was not an issue.
But, that wasn't all I ran into which you may already know.
I needed the following approvals:
1. UL approval for the plastic by itself at 94V-0 as a fire enclosure.
IIRC.
2. UL approval for the vendor facility to mix/make the plastic ensuring
the 94V rating of the plastic.
3. UL approval for the conductive coating by itself.
4. UL approval for the marriage of the specific plastic to the specific
coating.
5. UL approval for the vendor to apply the specific conductive coating
to the specific plastic at their facility.
And then of course, submit all the above to UL so get approval of all the
approvals.
Regards, Doug
From: Eric Henning <[email protected]>
To: '[email protected]'
Subject: plastic enclosures & grounding
List-Post: [email protected]
Date: Thursday, July 31, 1997 9:40 AM
Greetings all,
thanks to those who replied to my INMETRO request (INMETRO = Instituto
Nacional de Metrologia, Normalizacion e Qualidad
Industrial (of Brazil).
(From the name it appears to be analogous to our NIST)
Questions via e-mail to <[email protected]>
Website (in Portuguese) at: http://inmetro.gov.br
President
J#lio Cesar Carmo Bueno
Secretary: Icla
Phones: 223-8877/225-8032
Fax: 223-4283
(Thanks Rich and Art)
Now, a new question. We are designing our first all non-metallic enclosed
stand alone product and i am confused about the earth terminal. I don't
need
a protective earth terminal but need a functional earth terminal. There is
absolutely no metal frames, supports etc... The ground is needed for
cable
shields, transient protection, etc... So i need to bring ground into the
box.
Can i bring it in "normally" as the third conductor of the power lines
(Hot,
neutral, ground)? Only call it functional ground? If so do i need to
hi-pot
between H+N and this ground? Or do a double insulation test? What about
on
the 12V circuit that has transient protection to this functional ground?
I can't
run a dielectric test between signal and function ground as it will
naturally fail
thru the transient protection.
Your thougths please. This is a 120/240 VAc powered device.
thanks
eric
[email protected]
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