Loading ...
Sorry, an error occurred while loading the content.

Shielded Cable

Expand Messages
  • integrationx
    When will the BACnet MS/TP specifications (Section 9.2.1 Medium) be revised to delete the shield requirement. Structured cabling vendors certify that the
    Message 1 of 4 , Jul 23, 2007
    • 0 Attachment
      When will the BACnet MS/TP specifications (Section 9.2.1 Medium) be
      revised to delete the shield requirement.

      Structured cabling vendors certify that the unshielded twisted pair
      (UTP) CAT5 (or greater) installation will support EIA-485, however to
      conform to the BACnet MS/TP standard we require a shielded cable.

      This means BACnet MS/TP will be excluded from new installations where
      the BAS system cabling is written around ANSI/TIA/EIA 862.

      Any thoughts? Is this forum actually directly involved with the MS/TP
      standard?
    • Clifford.H.Copass@jci.com
      The MS/TP Working Group is starting to take a look at several cable related issues. Some installations work fine without a shield and some require a shield to
      Message 2 of 4 , Jul 24, 2007
      • 0 Attachment
        The MS/TP Working Group is starting to take a look at several cable related
        issues. Some installations work fine without a shield and some require a
        shield to handle electrical noise in the area. Some work fine with a
        simple twisted-pair signal conductor while others require the addition of a
        remote reference conductor. Devices are manufactured with two, three or
        even four wire termination points depending on the characteristics of the
        device and the type of environment it is intended to work in.

        I have started working on a proposal (as work assignments permit) along
        with someone from ABB. If you would like to contribute to the proposal, we
        would welcome meaningful input.

        The convener of the working group may also have some comment on this issue,
        but I will let him answer.

        Cliff Copass
        Johnson Controls, Inc.






        integrationx@yaho
        o.com
        Sent by: To
        bacnet-mstpwg@yah bacnet-mstpwg@yahoogroups.com
        oogroups.com cc

        Subject
        07/24/2007 01:59 [bacnet-mstpwg] Shielded Cable
        AM


        Please respond to
        bacnet-mstpwg@yah
        oogroups.com






        When will the BACnet MS/TP specifications (Section 9.2.1 Medium) be
        revised to delete the shield requirement.

        Structured cabling vendors certify that the unshielded twisted pair
        (UTP) CAT5 (or greater) installation will support EIA-485, however to
        conform to the BACnet MS/TP standard we require a shielded cable.

        This means BACnet MS/TP will be excluded from new installations where
        the BAS system cabling is written around ANSI/TIA/EIA 862.

        Any thoughts? Is this forum actually directly involved with the MS/TP
        standard?




        Yahoo! Groups Links
      • polars15213
        ... MS/TP ... YES, this forum represents the BACnet MS/TP Working Group and reports directly to the SSPC-135 that is tasked with continuous maintenance of the
        Message 3 of 4 , Jul 24, 2007
        • 0 Attachment
          --- In bacnet-mstpwg@yahoogroups.com, "integrationx" <integrationx@...>
          wrote:
          >
          > When will the BACnet MS/TP specifications (Section 9.2.1 Medium) be
          > revised to delete the shield requirement.
          >
          > Structured cabling vendors certify that the unshielded twisted pair
          > (UTP) CAT5 (or greater) installation will support EIA-485, however to
          > conform to the BACnet MS/TP standard we require a shielded cable.
          >
          > This means BACnet MS/TP will be excluded from new installations where
          > the BAS system cabling is written around ANSI/TIA/EIA 862.
          >
          > Any thoughts? Is this forum actually directly involved with the
          MS/TP
          > standard?
          >

          YES, this forum represents the BACnet MS/TP Working Group
          and reports directly to the SSPC-135 that is tasked with
          continuous maintenance of the BACnet standard.

          Despite the migration of TIA/EIA 862 to unshielded cable
          the consensus among participants in the SPC-135 and now
          SSPC-135 has always been to prefer the use of shielded cable.
          Part of the reason for this is that historically much of
          the environment within which MS/TP style networks are used
          has NOT been built around structured cabling, but instead
          is run through ceilings and around transient-generating sources
          in some cases using *questionable* practices. The use of shileding
          greatly improves performance under these conditions.

          Having said that, there is nothing stopping anyone from
          creating a proposal to be deliberated by the WG and perhaps
          becoming recommended to the SSPC. The normal practice in
          this SSPC for such proposals is to construct them using
          the formatting and language of the SSPC style guide,
          and submit the proposal to the relevant WG through a forum
          like this one. It is also helpful if the author can attend
          working group meetings to present their ideas.

          The next working group meetings are to be held in Atlanta
          in October, so there is time to prepare a proposal if
          you want to do so.

          What you are proposing though flies in the face of existing
          BACnet wiring practice that is in use in millions of installed
          nodes worldwide. As a result, I would expect some stiff
          resistance from existing manufacturers unless you can show
          some test data of how, if at all, the use of unshielded
          wiring would affect actual MS/TP networks in practice.
          I am just guessing, but I imagine that WG and SSPC members
          will be skeptical unless one can show "laboratory" tests
          of typical network, as well as "field" tests with accumulated
          statistics on frame performance etc.

          If you decide to make such a proposal, please post to this
          forum and we will assist in moving it to a proper hearing.

          David Fisher, Convener
          MS/TP Working Group
          dfisher@...
        • integrationx
          David, Thankyou for the response. I need to follow this through the proper channels internally to see whether it should be pursued. The world of standards is
          Message 4 of 4 , Jul 24, 2007
          • 0 Attachment
            David,

            Thankyou for the response. I need to follow this through the proper
            channels internally to see whether it should be pursued.

            The world of standards is an interesting one and, as I'm sure you
            appreciate, it is how these standards are interpreted and promoted by
            consulting engineers that ultimately effects the success or failure
            of a standards adoption.

            The case in point is typical. Consulting engineers in my region
            are 'adding' references to the ANSI/TIA-EIA 862 standard to their
            documents; down to the level of using structured cabling between
            field level devices. The problem I face is trying to explain why we
            cannot run BACnet MS/TP over unshielded cable. If I state that the
            BACnet MS/TP standard does not support it, the short answer I get is
            that they will exclude BACnet suppliers from the tender process and
            limit it to LON based products (as FT-10 Lon can run over Cat5e)

            Technically I am not in the field of evaluating or even understanding
            all of the electrical phenomenon surrounding shielding etc, so trying
            to present a case for it to be dropped from the BACnet standard for
            MS/TP is probably beyond my ability.

            Perhaps I need to look at the problem another way, and try to educate
            the consultant as to the benefits of shielding.
          Your message has been successfully submitted and would be delivered to recipients shortly.