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Send DMX over Bates?

Discussion in 'Lighting and Electrics' started by Rose03, Dec 7, 2018 at 9:52 AM.

  1. Rose03

    Rose03 Member

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    This is probably a terrible ideas but I want to know. Is it possible to send a 3pin dmx signal down a dimming circuit that is not connected to a dimmer? Would there be too much interference from other live circuits?
     
  2. sk8rsdad

    sk8rsdad Well-Known Member Premium Member Fight Leukemia

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    DMX uses the EIA-485 standard for data transmission. EIA-485 is inherently resistant to induced noise and very tolerant of poor conditions.

    However, it is a really bad idea (TM) to mix data and power, so much of a bad idea that the electrical code forbids it except in very controlled circumstances. There is a significant risk of electrocution and/or fire. In short, DON'T DO THIS!

    @sk8rsdad, P.Eng.
     
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  3. Rose03

    Rose03 Member

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    Thats what I thought, the only reason I entertained this idea was because the theater in question has a hard patch system allowing the circuits to be completely separated from power.
     
  4. CrazyTechie

    CrazyTechie Well-Known Member

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    Another thing to think about too is what happens to the receiving device when somebody accidentally sends 120v power into the DMX input. ;) If you're using the same connector for power and data I'd wager it's bound to happen at some point.

    Now I'm somewhat curious as to what would happen... :think:
     
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  5. SteveB

    SteveB Well-Known Member

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    So essentially you are thinking of using the in-place 120v dimming distribution wiring for data, under the assumption you can successfully isolate that particular 120v circuit, than adapt to be a DMX transmission cable ?.

    Lets hypothesize and say you get fired/car accident, etc.... and the folks at the theater "forget" that you were doing this. They then decide to re-purpose that 120v circuit for its intended purpose and accidentally send 120v to the very, very expensive devices on the receiving end.

    Is why it's a bad idea. Beside the fact that DMX, while being forgiving of bad cable, (somebody ran DMX over barbed wire) might just decide to stop being forgiving when used with #10 THHN, non-twisted pair, etc.....
     
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  6. FMEng

    FMEng Well-Known Member Fight Leukemia

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    The immunity to noise is dependent upon three factors, the balancing of the output and input stages, and the cabling ability to ensure the noise is induced identically in both wires of the pair. The twisting of the signal pair is what allows the circuit to cancel noise! Dimmer load wiring will not have any noise immunity at all because the amplitude and phase of noise induced in each wire will be different because their positions in raceways are random.

    We also know that DMX is sensitive to signal reflections. That's why the cable impedance and termination has to match or it doesn't work reliably. What's the impedance of a pair of #12 wires in a conduit?

    Not only is this a potential safety hazard, but it just plain will not work.
     

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