Sunday, May 1, 2011

Industrial Ethernet Reliability and Performance: Cable Terminations

This post may seem very obvious to some and completely foreign to others.  The majority of Ethernet infrastructure is general Cat 5/5e/6 (from here on I will refer to the categories only as Cat5) cabling.  Terminations for each category of cabling are essentially the same and often done incorrectly; it is something I have seen in manufacturing facilities time and time again.
There are generally two types of Cat5 cabling, solid core and stranded.  This is referring to the copper conductor in the eight wires that make up the cable.  Each type has a specific use.  Solid core Cat5 is intended for permanent installation, such as from a patch panel to another patch panel (or other permanently mounted termination such as a wall box).  Most often solid core wire is terminated by pressing each of the eight small wires between an individual set of blades that slice through the insulation and make contact with the copper conductor.  Another consideration with solid core wire is movement.  The solid conductors have a much higher possibility of breaking from excessive movement than stranded cable.  Solid core wire can be terminated with a male RJ-45 connector, but the connector must be specifically designed for solid core wire.
Stranded core cable is intended for port to field device connections.  The stranded wire can stand up to far more movement and vibration and has a tighter acceptable bend radius than solid core cable.  Stranded cabling is typically used in patch cables and terminated with a male RJ-45 connector.  Stranded cable is not intended for long runs as the electrical performance is poorer than that of solid core cable.
Incorrect Termination
Finally, the quality of the Cat5 cable used can make a significant difference in performance.  The outer jacketing should be pliable.  Some of the cheaper brands have a very brittle outer jacketing that can break in tight bends and get damaged as it is pulled through conduit leading to damage of the underlying twisted pairs.  Another feature that I find important is bonded pairs.  This means that the two wires in each of the four pairs are physical bonded to one another.  The benefit of this is that the twist construction of the cable is maintained better as the cable is bent.  Cable that does not feature pair bonding can actually have the pairs separate in bends which reduces cross talk cancelation.

[ Original Post by Jed Leviner] 


  1. Jeremy Gillett says:
    The use of the correct Ethernet cabling can be critical to creating a reliable network connection. I have been working as an engineer in the industrial automation controls field for more than 10 years. I have seen several occurrences where solid core wiring has not been landed to a stabile connection point or like the example of what not to use above. The outcome was a network connection that over time failed. The worst part has been the way the failures have occurred. For example we had a customer that called us in to help troubleshoot a drive problem. They have a few networked variable speed drives that were occasionally faulting. This was causing their cold rooms to fall out of spec limits. One of the main causes of the drives faulting ended up being the occasional loss of the network connectivity, and a simple correction to the Ethernet connection fixed the issue.
  2. Interesting article that was.
    One more point that i would like to add is the pins being used.
    1,2 form one twisted pair and 3,6 form another twisted par.
    Hence the wiring on both sides to be maintained in same pair.

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