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In the comments on this question (Using PEX as wire conduit), the issue of grounding shielded data cables on one end vs both ends came up.

For any arrangement of cables (ex. single cable, multiple cables into splitters/hubs, multiple parallel cables. etc.), how should they be grounded?

I am especially interested in both CAT6 (Ethernet) and coax (<3GHz) since I am actually about to run some underground between two different structures. In my case, both structures share a grounding electrode system, but an ideal answer would also address instances where this is not the case.

My current plan is to ground the coax on both ends with a grounding block and a grounding conductor going back to the nearest service panel, and to ground the CAT6, which is shielded, on both ends with surge protectors and a grounding conductor going back to the nearest service panel.

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  • My experience is with an RS485 data cable for some process control equipment. With neither end grounded nothing worked, with both ends grounded it was slow and error ridden, but kind of worked. Then someone told us to ground only one end, and it started working exactly correctly. Somewhere along the way a different vendor replaced the cable with unshielded cat 5e, that wasn’t working until someone realized they had used an odd pair that wasn’t twisted, when we made the data pair green/green-white it worked again but never as well as the original shielded at one end untwisted data cable.
    – Tyson
    Commented Jun 11, 2018 at 2:14
  • One theory evaluating the above is that in a perfect world grounding both ends would make no difference, but it’s possible that one ground or the other isn’t perfect, leaving potential between.
    – Tyson
    Commented Jun 11, 2018 at 2:16
  • @Tyson I see your point in that grounding to different potentials can be a problem. Also, it seems (especially in the system I describe) that I will also be creating a ground loop, which is notorious for signal problems but only for single-end communication. Because Ethernet is differential and only the shield is actually grounded at each end, I can't see why it would be a problem. I can see how it could be a problem for coax, however, since that is single-end communication.
    – Hari
    Commented Jun 11, 2018 at 4:06
  • One of the two satellite TV providers in the USA at one point changed grounding on its receivers to 3-prong cords. This created 2 ground points, the wall plug and the coax ground block. They found out how bad residential grounding really is (think old houses-not newer houses). After a fire or 2 they shifted to wall warts and cord bricks so that the receivers themselves no longer required grounding via the wall plug, instead relying only on the coax ground block.
    – Tyson
    Commented Jun 11, 2018 at 10:09

2 Answers 2

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The industry practice is to ground the main panel end and leave the field end ungrounded.

If you ground both ends you create an antenna for RF interference. Search the web for dipole antenna design.

Good luck!

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@ArchonOSX is correct. The main reason you only ground one end is that the shield is not a ground it is a drain. It catches interference in the air and drains it to the ground. It is called a family connection so you should which ground whichever father upstream than the other and ground to that electrode. In you case I would select which structure you main panel is in (mother to daughter).

Good Luck.

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