RE: PCI compliance and UL approval - is it possible?

[471034N@knotes.kodak.com]

From: Irv D Negrin

Dan,

I am just stating my experience with UL.  I don't know for certain why UL
is not concerned about the scenario you state but PCI boards are UL
recognized without fuses.  I was just answering the question of how to get
UL approval on an add-in card.  In fact, I have never encountered a PCI  or
any other pc add-in card (although one may exist) that had fuses on the
power connections.  The only time I've seen fuses on a card is if it
supplied power to an external device through an interface cable.  An
example would be termination power on a SCSI interface.

Based on my experience, I guess it would incumbent on the system designer
to resolve the issue as necessary to get UL listing for the complete
system.  This may include adding fuses to the back plane to reduce the
potential current seen by any one add-in card.  I suppose UL doesn't place
that burden on the board designer and hence the recognition mark, not the
listing mark.  Also, UL does recognize that not all short conditions can be
protected, hence the flame rating on the board material.   The board is
allowed to overheat, even smoke as long as it doesn't burst into flames.
UL doesn't certify the system will continue to function after an event,
only that it will remain safe.

Irv Negrin
Eastman Kodak Company
Health Imaging Division
471034N@knotes.kodak.com


     When I think of a passive backplane with 10 slots, it seems to me
that that system
     should provide a 5 volt rail capable of supplying 50 amperes.
Without fusing, you
     could be exposing your board to that full 50 amperes before the
power supply shuts
     down. If your board shorts to 1/10 of an Ohm or more, then the power
supply would
     not shut down, and your board could overheat.

     Why do we see so many PCI boards without fuses?

     Regards,
     Dan

     danstew@nortelnetworks.com
     Nortel Networks,
     Ottawa, Canada.