CBUS Cable Length and Network bridges

Discussion in 'C-Bus Wired Hardware' started by Roosta, Jul 20, 2016.

  1. Roosta

    Roosta

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    Hey guys,

    One for the gurus as I am getting rusty ;-)

    I have been pulled into a project.. Situation is a geographical large commercial site.. Total units is below 40 however total cable length is probably going to be around 3.5kms so the plan was to split the network up into about 7 by using network bridges, however some distances of the cable between distribution boards is upwards of 800m of underground jelly filled cat5..

    So my question is if there is a power supply at each end of the run and there is no cbus device in between can the cbus comms make the distance of 800m?

    All advice appreciated..

    Cheers..
     
    Roosta, Jul 20, 2016
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  2. Roosta

    ashleigh Moderator

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    Yep. Cable length is 1 km, and you could even have a PS at only one end, depending on total number of units / current draw. This might be pushing things a bit though.

    So having one each end may be a bit over the top but it will certainly ensure robustness in the event of a single PS failure, or the cable getting chopped, or similar.
     
    ashleigh, Jul 21, 2016
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  3. Roosta

    NickD Moderator

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    Yes. C-Bus doesn't rely on nodes to repeat messages. The cable length limitation is just down to propagation delay/network impedance.

    You shouldn't need a power supply at both ends either.. the voltage drop will be negligible if there in only one bridge drawing 18mA at the far end... from memory CAT5 is 19 ohm/km so you'd only be looking at < 0.3V drop.

    Nick
     
    NickD, Jul 21, 2016
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  4. Roosta

    znelbok

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    Sorry, cant answer for you, but if there ever was a need for a fibre bridge this would be it.

    An underground cable with a good thunderstorm could cause havoc.
     
    znelbok, Jul 21, 2016
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  5. Roosta

    Roosta

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    Hey Guys,

    Thanks for the replies.. You confirmed my thoughts which is awesome.. Even my suspicions of whether a psu at each end was necessary, i was just considering that for good measure..

    Luckily the long runs are purely for operating relays which inturn operate lighting and a small delay is acceptable..

    Indeed originally the project would have been much easier with a CBUS to Fibre link as there will be fibre at each DB anyways but unfortunuately such a beast doesnt exist 'out of the box'..

    Thanks again..
     
    Roosta, Jul 21, 2016
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