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

Barton F Bruce barton at gnaps.com
Wed Apr 10 20:14:01 UTC 2002


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

This does NOT apply to telco cables run outside, often run on the same poles
parallel to power wires for miles, grounded at many points in a MGN (Multi
Grounded Neutral) environment where, like it or not, the earth carries
considerable current.

Opening a shield ground in this environment is bad.

----- Original Message -----
From: "Kevin Oberman" <oberman at es.net>
To: "Christopher K. Neitzert" <chris at neitzert.com>
Cc: <nanog at merit.edu>
Sent: Wednesday, April 10, 2002 2:17 PM
Subject: Re: Sheilded Cat-5E Ground Loop - Myth or Reality?


> *This message was transferred with a trial version of CommuniGate(tm) Pro*
>
> > Date: Wed, 10 Apr 2002 17:43:50 +0000 (UTC)
> > From: "Christopher K. Neitzert" <chris at neitzert.com>
> > Sender: owner-nanog at merit.edu
> >
> > 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: oberman at es.net Phone: +1 510 486-8634
>





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