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Re: Sheilded Cat-5E Ground Loop - Myth or Reality?

  • From: Kevin Oberman
  • Date: Wed Apr 10 14:23:08 2002

> Date: Wed, 10 Apr 2002 17:43:50 +0000 (UTC)
> From: "Christopher K. Neitzert" <[email protected]>
> Sender: [email protected]
> I'm in the process of managing cabling for a large install (500-ish runs)
> and a vendor came to me with a story about the creation of ground loops in
> running sheilded+gounded cat-5e in large installations.
> Does anyone have any experiences they would like to share regarding this?

Just follow standard rules for grounding. If the shield is connected
to anything, it should only be connected at one end! This is really
always true, but is especially true when there is significant physical
distance involved as this can result in current flow between the
grounds. This will almost certainly create a significant hum
field. Due to its excellent common mode rejection, this may not be a
real problem, but it always deteriorates S/N margins to some extent.

There is also a REAL safety issue! Make sure that ground is NOT
exposed at the un-grounded end. A potential of many volts can occur,
especially in areas subject to thunder storms.

None of his is specific to Cat-5e installations but is common to ALL
electrical installations.

R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: [email protected]			Phone: +1 510 486-8634