Hello Chris
In an ideal world. The Ethernet cables would all be enclosed in metal conduit
or cable trays.
Routed only with similar communications and signal level circuits. The
Cabinets would all have
provisions to either ground or capacitively couple any cable shields. And the
final connections
would all be made via patch cables, which in the LV Comm Cabinate wouldn't
require shielding.
Nor would the 90meter cables in conduit.
But how will your customer actually expect to use it?
Cable nicely coiled and Tie-Wrapped almost a meter away from the Medium
Voltage Disconnect?
Cable run bundled with the 480VAC and/or Spot Welder cables? Will there be
any transient
protection on the Contactors/starters? What is the expected operation of the
system during
spurious events such as lightning storms? Can your Ethernet ports handle Surge
for Unshielded
Cables?
I believe the ODVA had concidered a Ethernet/IP Standard where a Single Point
grounding system
was created by Grounding the Switch and leaving the Nodes to Capacatively
Couple the Shield.
Although when implementing RSTP this defeats the principal. FWIW my own
philosophy is to treat
small machines (10meters?) as a Mesh and ground everything, everywhere to
create a single
ground node. And when it becomes a transmission line to break the ground
loops, preferably by
Fibre.
Regards,
John
______________________________________
______________________________________________
John Merrill | Schneider Electric | Process & Machine Business |
Principal Product
Safety Engineer
Phone: 978-975-9710 ext. 9710 |
Email: john.merr...@us.schneider-electric.com | Site:
www.schneider-electric.com |
Address: M.S. 7-1B, 1 High Street, North Andover, MA 01845 USA
*** Please consider the environment before printing this e-mail
"Chris Wells"
<radioactive55man@c To:
<EMC-PSTC@LISTSERV.IEEE.ORG>
omcast.net> cc:
<christopherdwe...@eaton.com>
Sent by: Subject: Shield bonding
on STP Cat5
Ethernet cables
emc-p...@ieee.org
11/24/2010 02:22 PM
I am looking for some feedback on the proper/practical treatment of Ethernet
STP Cat5 cable shields. The interfaces are running 100 Base Tx. The STP
cables typically are DC grounded at each end to the RJ45 jack and then often
metal shield fingers contact a metal housing that is grounded. From a High
Frequency point of view this works well but what about differences in local
grounds at each end? Is Ethernet affected by shield noise due to ground
loops?
I put Ethernet into Commercial and Industrial power distribution
applications for monitoring purposes. At a site we typically have islands
of localized well bonded distribution gear that is actually bolted together
with ground bus bars. There may be several of these in one location but
then some separation between building wings.
What we have been recommending is that one can use STP within a local
assembly gear line ups but when leaving use Fiber Optic instead. This has
worked well but there is always an economic pressure to cut out the FO up
link.
We also use multipoint RS485 serial communication links in our power gear
that can go thousands of feet between separate gear line ups.
In this application we reference shield at each tap AC to ground through a
surge rated cap or 4.7 to perhaps 10 nF to ground. Also the RS485 nodes are
electrically isolated. This approach blocks power ground loops but helps us
deal with Electrical Fast transient or RF conducted EMI type exposures. It
appears to be most meaningful from around 100KHz up to perhaps 10MHz.
Does this AC shield approach translate into Ethernet? How do others deal
with the treatment of shields for Cat5 Ethernet in noisy wide spread
applications like this? Are there IEEE Standards on Cat5 STP shield
treatment that I should be looking at?
Thanks
Chris Wells
Eaton Corp.
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