Practical question on cable lengths ...

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  • chris_j_hunter
    Automated Home Legend
    • Dec 2007
    • 1713

    Practical question on cable lengths ...

    just trying to get a handle on how far (eg) reed-switches can be away from modules - DFP, or ODI, or whatever - we've trawled through lots & lots of documentation, and not seen an answer - could have missed of it, of course, but how many meters might be OK, and what sort of cable - Cat-5e UTP or STP, or bell-wire, or ... how far away have people tried, with success ?

    please !

    Chris
    Our self-build - going further with HA...
  • chris_j_hunter
    Automated Home Legend
    • Dec 2007
    • 1713

    #2
    to answer my own question - the answer's in the datasheets at :

    Older Datasheets Datasheets for older products can be found here.


    in the how-to-wire guides ... eg: the one for the MFP module includes the following :

    "In addition, the MFP provides two digital inputs which can be used to connect to any switch inputs such as door contacts, break glass, pressure mats etc. The connection to these should use suitable wire e.g. alarm cable. Long cable runs (>10m), or cable runs passing close to strong sources of electrical noise (e.g. mains wiring) may benefit from a shielded cable. In general this is not necessary and the choice of colours is arbitrary, but it should be consistent throughout the property to make testing easier ... "

    obviously !
    Our self-build - going further with HA...

    Comment

    • Karam
      Automated Home Legend
      • Mar 2005
      • 863

      #3
      Apologies for not replying to this one earlier. Yes it is a case to some extent of being sensible.

      - Never run any low voltage signal cable adjacent, particularly in parallel to mains cable, or cable which might be carrying heavy switched currents even if low voltage. If you really must and cannot maintain a separation of say 15cm, then shielded cable is the next option. The shield should ideally connect back to the central earthing point in some way (eg. via an IDRANet cable shield if utilised).
      - If two cables have to share the same space and are not restrained such that they cannot touch each other then the insulation on both should be rated to the highest voltage in any of the conductors. 'Rated to' does not mean equal to ie. mains rated will probably have to withstand KV not just 240V.
      - Cat 5 cable probably has an advantage over burglar alarm cable because using a twisted pair for each sensor rather than just having a common return for several sensors can have some noise reducing characteristics. Similarly shielded cable can help if used properly. But in general basic bell wire or burglar alarm cable will do just fine for short runs of up to a few meters. If you find you have to run sensor cable over long distances you might consider putting a module closer to the sensor since digital transmission over IDRANet is much more robust than that from a sensor to an input. That's the whole point ..
      - If you find yourself having transgressed these guidelines or still getting noise problems for some reasons then extra filtering can be applied at the input either to a limited extent via module parameter adjustments or by physical components.

      Comment

      • chris_j_hunter
        Automated Home Legend
        • Dec 2007
        • 1713

        #4
        many thanks, useful ... not sure we can afford to have a module right next to every reed switch or push-button or mat, and I guess we're not alone in this ! ... ie: so looks like the general silence from the many who now have installations on the go must imply no difficult issues have been encountered in running wires (bell-wire, mostly, cat-5 sometimes, shielded cat-5 occasionally) for maybe a metre or two (four, or six, even) away from modules, in a variety of situations ! As they say, no news is good news ...
        Last edited by chris_j_hunter; 27 October 2009, 04:06 PM.
        Our self-build - going further with HA...

        Comment

        • Karam
          Automated Home Legend
          • Mar 2005
          • 863

          #5
          Perhaps a useful analogue is a standard burglar alarm system. These tend to be centralised with several meters to the sensors often just using very basic unshielded cable. I don't think the sense impedances are much different so should be about similar performance.

          Comment

          • katman
            Moderator
            • Jan 2004
            • 247

            #6
            If you did want reed switches or push-buttons or mats some considerable distance from your HA system (cant comment specifically on idratek as I dont have it but principles apply to all systems with contact closures) then you could always use that contact closure with a small power supply to drive either a small relay or preferabley the LED of an opto isolator. The output of the relay/opto can then be connected to the HA system and not only provides total immunity to noise and RFI but also provides electrical isolation as well.

            Just adding another option
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            Comment

            • chris_j_hunter
              Automated Home Legend
              • Dec 2007
              • 1713

              #7
              thanks, good thinking !
              Our self-build - going further with HA...

              Comment

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