Brian,
You have cited the only reference that might construe concern of these
fingers, however, I do not know what you mean by "if correctly
designed-in". You also did not elaborate on the performance difference
between the 2 gasket materials.
Please note that the 2nd paragragh of 1.3.1 of UL 1950 states "Where the
equipment involves technologies and materials or methods of construction
not specifically covered, the equipment shall provide a level of safety
not
less than that generally afforded by this standard and the Principles of
Safety contained herein."
This might be indicating that, in the context of 4.1.4, the delineation
between OPERATOR and SERVICE PERSONNEL may not be as black & white as you
have depicted, but a bit muddied. Granted, it is expected that service
people are better trained technically than operators. Also granted that
service people know of this type of risk and can work around it. But
because of that, don't expose them to a known and possibly hidden risk.
I'm
sure that they wouldn't appreciate it.
Some experience that I've had in a past life with finger gaskets of this
type has been that they are easliy damaged through handling and then
become
more of a hazard with broken finger stubs producing sheared edges.
Bear in mind that there are indeed alternatives to adequate shielding of
this type, with the foam being only one.
Also, what is the difficulty for not wanting to provide to the customer
what he wants?
So much for my opinionated 2 cents worth.
Regards,
Ron Pickard
[email protected]
______________________________ Reply Separator _________________________________
Subject: FW: EMI gaskets
Author: <[email protected]> at INTERNET
List-Post: [email protected]
Date: 3/18/98 12:29 PM
-
Subject: EMI gaskets
I am interested in hearing the experiences of anybody out there who has
had a need for using EMI gaskets, in particular between metal
faceplates of circuit packs in a Telecomms Sub-rack.
We have evaluated BeCu finger stock and foam covered with a metallised
fabric and have found the metal fingers out-performed the foam. But,
due to customer complaints relating to safety hazards posed by the
metal fingers we are being pressured to use the foam. Has anybody else
faced similar problems ?
>From our experience, if the fingers are designed suitably for the
application and applied correctly there should not be a hazard. My
reading of IEC950/EN60950/UL1950 does not indicate any prohibitive clause
relating to metal fingers. The closest (4.1.4) only stipulates protection
of the OPERATOR and does not refer to SERVICE PERSONNEL, who would be the
only persons exposed to the risk i.e. it is only when a module is
withdrawn from a shelf that the fingers are exposed (our equipment is
Central Office type).
Does anybody know of any safety/regulatory objective reasoning for not
using fingers, if correctly designed-in, in an application such as ours
?
Regards,
Brian McAuliffe
Regulatory Engineering
Tellabs Ltd
Tel: +353.61.703269
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