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Thread: Shielded Twisted Pair Cable

  1. #1
    Automated Home Legend Paul_B's Avatar
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    Default Shielded Twisted Pair Cable

    When I started my Idratek installation I decided on using Shielded Twisted Pair cable. The screenshots from Karam show double cabling to the connector and the two shielded strands twisted together. Termination occuring just at the the power module into the 0V connection.

    I've decided to use single connections as I didn't trust my skills on doubling up cables. But now I am not sure how to wire the shielded strands and where to terminate. Any guidance would be appreciated.

    Paul

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    Automated Home Legend chris_j_hunter's Avatar
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    Default Shielded Twisted Pair Cable

    we'll be buying our Cat-5 shortly, but haven't quite bottomed all the issues (type, quality, plugs, tools, etc) ... one of the many questions being shielded or not, obviously ... think we'll go unshielded, because when I broached the subject on AH a month or two ago, opinion (so far as it was expressed) was that sometimes it could be necessary, but generally it was to be avoided, because it could introduce problems of its own (noise / interference of some sort) ... not sure if that means it could be best not to terminate the shielding, maybe that would introduce problems, too ... but otherwise, grounding is usually done at one end only, presumably the power-module end, in this case, because it would provide the better ground - a key thing being to avoid earth-loops & associated resonances !

    HTH - sorry if it's nothing new - just noticed 'no replies so far !

  3. #3
    Automated Home Legend Paul_B's Avatar
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    Just confused if I only use one cable but string this along which ones should be terminated and which ones shouldn't.

    So a single cable from PDU to module is terminated to 0V on the PDU connector but not the module connector?

    If a cable runs from PDU to patch panel to module where do I terminate in this instance?

    Finally, if a cable runs from PDU to patch panel to another patch panel and then to a module which connectors should be terminated?

    Paul

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    Automated Home Legend chris_j_hunter's Avatar
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    Default Shielded Twisted Pair Cable

    PDU PDU PDU, I would say, all joined-up, through intermediate items, but terminate only at the PDU end - would be my guess ... but, actually, I think I would ask Karam !

    'did some Google digging on shielded / unshielded today ... most often people seemed to say no need for shielding, unless very special circumstances ... I never felt I'd bottomed the issue ... and Gefen seem to use shielded, at least for AV distribution ! So we're still undecided ...

  5. #5
    Automated Home Sr Member n07tv's Avatar
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    Default Where to terminate

    Paul,

    Tying the drain shield wire to 0V back at the PSU, but leaving the last position (i.e. last module of the spur) usually works best. This was common practice in both the fire alarm and access control industries, both of which I spent several years doing installations at many sites. For modules that are along 'the dasiy chain' tying the drain shields together but not to 0V seems the best idea.

    The reasoning is to provide a 'faraday cage' around the signals to minimise emissions and susceptibility. Fastening both ends could potentially provide earth loops which can create other issues.

    Despite all this, I would have to agree with Chris and say that I have never seen a definitive answer, so using best practice always seems a sensible compromise.

    HTH,
    n.

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    Moderator Gumby's Avatar
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    Normally the discussions for screened vs unscreened relate to the use of CAT-5 for Ethernet. My suspicion with Idranet is the audio bus might be the most likely to show any signs of interference and is probably more susceptible than either Ethernet or the Idranet databus.

    Given the recommendations for screened cable from Idratek, I'm surprised the PWA patch panels don't have a facility for commoning the drains - or has this been added.

    Of course, my installation has used unscreened throughout, with the exception of a long run down to the shed. But then I don't use MFPs, so couldn't tell how affected the audio bus might be. I guess this might change with DFPs coming out.

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    Moderator Gumby's Avatar
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    Forgot to say, the recommendation to tie drains to 0V at power supply end and then ensure drain continuity across any joins/patching sounds correct to me.

    The reason to tie drain at only one end is to avoid the creation of a ground loop.

    I suspect that joining the drain to 0v at the module end (topologicially equivalent) will create noise issues due to the impedance of the 0v wire.

  8. #8
    Automated Home Legend Paul_B's Avatar
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    Thanks for the opinions guys. It makes lots of sense.

    I guess the Idratek guys are on a well deserved break, but I'll try and touch base with Karam when he returns.

    My biggest issue is connecting all the drains together in the 6-way patch panel, I'm starting to thing of using a central connector with the drain cable longer than the cables to the connectors

  9. #9
    Automated Home Legend chris_j_hunter's Avatar
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    Default Shielded Twisted Pair Cable

    Paul -

    just in case, and picking-up on something David mentioned ... 'see Idratek have expanded their list of how-to PDFs ... I certainly didn't know it covered so many things ...

    http://www.idratek.com/DLGuidelines.htm

    Chris

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