Sheilded Cat-5E Ground Loop - Myth or Reality?
Hi 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? thanks christopher Christopher K. Neitzert / 0xC10D222F / chris@neitzert.com
Date: Wed, 10 Apr 2002 17:43:50 +0000 (UTC) From: "Christopher K. Neitzert" <chris@neitzert.com> Sender: owner-nanog@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@es.net Phone: +1 510 486-8634
None of his is specific to Cat-5e installations but is common to ALL electrical installations.
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Date: Wed, 10 Apr 2002 17:43:50 +0000 (UTC) From: "Christopher K. Neitzert" <chris@neitzert.com> Sender: owner-nanog@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 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@es.net> To: "Christopher K. Neitzert" <chris@neitzert.com> Cc: <nanog@merit.edu> Sent: Wednesday, April 10, 2002 2:17 PM Subject: Re: Sheilded Cat-5E Ground Loop - Myth or Reality? 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@es.net Phone: +1 510 486-8634
From: "Barton F Bruce" <barton@gnaps.com> Date: Wed, 10 Apr 2002 16:14:01 -0400 Sender: owner-nanog@merit.edu
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.
Shielded/screened TP on utility poles? This is an insane thing to do. It violates more rules than I want to even start to think about! Telco wires are always connected to lightning arrestors at the termination of the long run. (This is NOT always the same as the demarc!) MGN is MANDITORY. This is not a do-it-yourself project. Similarly, you should not do this between buildings either! (It would probably not be a problem running the the garage, but if the next building is on a different transformer...You could easily melt the wires or burn something. Or, to put it in simpler term, "Don't try this at home, kids!". It could prove fatal. (Hint, power lines are always at the TOP of utility poles and gravity works.) R. Kevin Oberman, Network Engineer Energy Sciences Network (ESnet) Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab) E-mail: oberman@es.net Phone: +1 510 486-8634
I was simply pointing out that "ALL electrical installations" seemed a tad too broad.
Shielded/screened TP on utility poles? This is an insane thing to do. It violates more rules than I want to even start to think about! Telco wires are always connected to lightning arrestors at the termination of the long run. (This is NOT always the same as the demarc!) MGN is MANDITORY. This is not a do-it-yourself project.
From: "Barton F Bruce" <barton@gnaps.com> Date: Wed, 10 Apr 2002 16:14:01 -0400 Sender: owner-nanog@merit.edu
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
The telco outside plant cables are all shielded. Generally one shield over all, but there are special purpose cables (Z or D screen often in a trademarked name) that have two seperate shielded compartments to eliminate near end crosstalk on low pair count cables where opposite side of the cable binder-group seperation in not sufficient for T1s or T1Cs. The shield on outside plant telco cables is not just an electrostatic shield (where one end grounding works) but is also part of a hum bucking strategy where the shield shorted to ground at both ends is exposed to the same powerline magnetic fields as the pairs within, and with the shield intentionally shorted (however imperfectly) end to end via ground, the resulting magnetic field bucks some of what would otherwise get into your pairs. Whether ISP or CLEC or both, I suspect a lot of us run into this kind of wiring quite often. ----- Original Message ----- From: "Kevin Oberman" <oberman@es.net> To: "Barton F Bruce" <barton@gnaps.com> Cc: "Christopher K. Neitzert" <chris@neitzert.com>; <nanog@merit.edu> Sent: Wednesday, April 10, 2002 4:37 PM Subject: Re: Sheilded Cat-5E Ground Loop - Myth or Reality? 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.
Shielded/screened TP on utility poles? This is an insane thing to do. It violates more rules than I want to even start to think about! Telco wires are always connected to lightning arrestors at the termination of the long run. (This is NOT always the same as the demarc!) MGN is MANDITORY. This is not a do-it-yourself project.
Similarly, you should not do this between buildings either! (It would probably not be a problem running the the garage, but if the next building is on a different transformer...You could easily melt the wires or burn something.
Or, to put it in simpler term, "Don't try this at home, kids!". It could prove fatal. (Hint, power lines are always at the TOP of utility poles and gravity works.)
R. Kevin Oberman, Network Engineer Energy Sciences Network (ESnet) Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab) E-mail: oberman@es.net Phone: +1 510 486-8634
From: "Barton F Bruce" <barton@gnaps.com> Date: Wed, 10 Apr 2002 17:04:50 -0400 Sender: owner-nanog@merit.edu
I was simply pointing out that "ALL electrical installations" seemed a tad too broad.
Shielded/screened TP on utility poles? This is an insane thing to do. It violates more rules than I want to even start to think about! Telco wires are always connected to lightning arrestors at the termination of the long run. (This is NOT always the same as the demarc!) MGN is MANDITORY. This is not a do-it-yourself project.
I was unclear. I meant that do-it-yourself utility pole installations were an insane idea. Telcos do deal with this routinely. R. Kevin Oberman, Network Engineer Energy Sciences Network (ESnet) Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab) E-mail: oberman@es.net Phone: +1 510 486-8634
On Wed, 10 Apr 2002, a half-million replies were made to this thread:
Date: Wed, 10 Apr 2002 15:03:00 -0700 From: half of the nanog list <everyone@everywhere.org> To: "Christopher K. Neitzert" <chris@neitzert.com>, nanog@merit.edu Subject: Re: Sheilded Cat-5E Ground Loop - Myth or Reality?
Thanks NANOG! Although some of these replies go way above my need on the physical layer, this has been most educational and informative. best wishes christopher Christopher K. Neitzert / 0xC10D222F / chris@neitzert.com director, network operations \ redundant networks http://www.redundant.com / cneitzert@redundant.com
If you use that sand-based media instead of the copper; you'll avoid LOTS of issues -- ground loops, induced noise, corrosion resistance, etc... Fiber Is Your Friend. -- A host is a host from coast to coast.................wb8foz@nrk.com & no one will talk to a host that's close........[v].(301) 56-LINUX Unless the host (that isn't close).........................pob 1433 is busy, hung or dead....................................20915-1433
On Wed, 10 Apr 2002 18:17:01 -0400 (EDT), David Lesher wrote:
If you use that sand-based media instead of the copper; you'll avoid LOTS of issues -- ground loops, induced noise, corrosion resistance, etc...
Fiber Is Your Friend.
You do have to worry about shark attack though. DS
On Wed, 10 Apr 2002, Christopher K. Neitzert wrote:
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.
While working at a previous employer, I had the privilege of hiring Ralph Morrison to look at grounding in our facility. I spent some time with Mr. Morrison talking about different methods used in large installations. It was a great learning experience. If you don't know Mr. Morrison, check out a few of his books on the subject. The short answer is follow the equipment manufacturer's directions and the local electrical code (usually the NEC in the USA). If you are unsure, you need to ask the manufacturer and a licensed professional for recommendations for your specific situation. The problem is there are many theoretically correct answers. There are lots of methods which will work under specific conditions. But will go tragically wrong when those conditions aren't met. BICSI, Telecommunications Cabling Installation Manual NFPA 70, National Electrical Code IEEE Std 1100, IEEE Recommended Practice for Powering and Grounding Sensitive Electronic Equipment IEEE Std 142, IEEE Recommended Practice for Grounding of Industrial and commercial Power systems Mil HDBK 419, Grounding, Bonding, and Shielding for Electronic Equipment and Facilities Federal Information Processing Standards Publication 94, Guideline on Electrical Power for ADP Installations (A bit out of date, but explains where some of the weirder stories come from) The following are a bit dry, but if you want definitive information TIA/EIA-568-A, Commercial Building Telecommunications Cabling Standard TIA/EIA-569-A, Commercial Building Standard for Telecommunications Pathways and Spaces TIA/EIA-570-A, Residential and Light Commercial Telecommunication Wiring Standard TIA/EIA-607, Commercial Building Grounding/Bonding Requirements for Telecommunications TIA/EIA-758, Customer-Owned Outside Plant Telecommunications Cabling Standard IS0/IEC 11801, Generic Cabling for Customer Premises
participants (6)
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Barton F Bruce -
Christopher K. Neitzert -
David Lesher -
David Schwartz -
Kevin Oberman -
Sean Donelan