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10/100Base-T electrical isolation specification

Posted on 2011-03-07
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Last Modified: 2012-05-11
I wish to know the specification that Ethernet adapter manufacturers should comply with regarding the electrical insulation/isolation between the data cable (RJ45 socket) connections and the Ethernet adapter circuitry earth.
Specifically the maximum permitted voltage and typical insulation resistance.
I am asking this question because the is an issue of un-reliable Ethernet comms between a local area network and a particular industrial control equipment (Omron) and one of the engineers has suggested that it might be an "Earth loop" problem.
Personally, I think that this is highly unlikely as there are several other industrial equipments on the same site that use the local area network without any problems and the eqipments are earthed quite well.
the site uses Cisco Catalyst Ethernet switches model 3650G
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Question by:alcindor
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LVL 34

Expert Comment

by:Istvan Kalmar
ID: 35061532
Hi,

I advis to use optical patches, and you able to makre real isolation!
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Author Comment

by:alcindor
ID: 35062119
That does not answer my question.
I wish to know the electrical insulation characteristics of 10/100Base-T Ethernet adapters.
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LVL 34

Expert Comment

by:Istvan Kalmar
ID: 35062169
if you afraid any earth loop problem you need to use optical connections with media converters!
Here is a data sheet:

http://www.blackbox.com/Store/Detail.aspx/Ethernet-Data-Isolator-10BASE-T-100BASE-TX/SP426A
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Author Comment

by:alcindor
ID: 35062551
I'm sorry but you still aven't answered my question.
I am not looking for a suggested solution to the problem.
I want to know the electrical insulation characteristics of the Ethernet circuits so that we can investigate and determine whether or not the differences in "Earth"potentials between the two equipments might be an issue.
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Accepted Solution

by:
CompProbSolv earned 1000 total points
ID: 35062918
According to page 339 of:
http://standards.ieee.org/getieee802/download/802.3-2008_section1.pdf
the spec (for 10baseT) is 25V ptp at 500kHz or lower

Page 491 of:
http://standards.ieee.org/getieee802/download/802.3-2008_section2.pdf
shows a similar spec for 10baseT
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Author Closing Comment

by:alcindor
ID: 35063335
Exactly what I wanted,  thanks for your help.

Roger
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