The above Ad will no longer appear after you Sign Up for Free!

Control/Dimming DMX shielding?

Discussion in 'Lighting and Electrics' started by jerekb, Mar 31, 2009.

  1. jerekb

    jerekb Member

    Messages:
    69
    Likes Received:
    2
    Location:
    Woodland Park/Aurora, CO
    So I have my DMX and a few other cables running through some conduit and in there is wiring for the things like power plugs and such with very little shielding is any at all. Is there a problem with DMX being near these other wires? It shouldn't be anything like needing to shield XLR correct?
     
  2. porkchop

    porkchop Well-Known Member

    Messages:
    1,812
    Likes Received:
    486
    Location:
    Vegas
    In theory no you don't need to shield cables sending DMX signal. Audio signal in my understanding is mostly an analog signal (think any decimal value between 0 and 1) and therefore very easily influenced by electric and magnetic fields surrounding it. DMX signal on the other hand is a digital signal (0 or 1, no other options) and is more robust. DMX doesn't have any error checking so if you had some really wonky power you could see interesting things happen. My suggestion would be if you can easily get the wiring away from the other lines then it's worth doing to prevent a very unlikely bad data situation from happening, but given that the situation is very unlikely, if it's going to take a while, or any amount of money not considered petty cash, I'd just depend on the robust nature of digital signal.

    As a side note, XLR is a common style of connector. Audio signal is most commonly sent through cables that have 3 pin XLR connectors on them. DMX signal is most commonly sent through cables that have 5 pin XLR connectors on them. Saying "Shielding XLR" doesn't actually make any sense when you're talking about shielding cable used for audio signal vs DMX signal as they are both sent through cables that have XLR connector. Stagehand slag has decided that "XLR cable" is a cable with 3 pin XLR connectors that is suitable for transmission of audio signal and "DMX cable" is a cable suitable for transmission of DMX signal usually, but not always, having 5 pin XLR connectors. I understood what you meant, I think, it's just a really big pet-peeve that I have developed because of some pretentious sound guys.
     
    jerekb and (deleted member) like this.
  3. Chris15

    Chris15 CBMod CB Mods Premium Member

    Messages:
    4,140
    Likes Received:
    416
    Location:
    Sydney, Australia
    Um, running what is fundamentally a telecomms cable (DMX) with mains in a conduit is not legal at least here in Aus.

    Now, that aside, the current DMX spec allows for the running of DMX down stock standard Cat 5 UTP. No shield needed but you do connect a ground wire. Remember that unless you are requesting lots of issues, use a proper pair for the data lines 2&3 and pair 2 on 4&5 of the XLRs. By rights pair 1 should be blue and pair 2 orange, pair 3 is green, so one should logically stick the ground on there...
     
  4. JD

    JD Well-Known Member

    Messages:
    4,029
    Likes Received:
    1,253
    Location:
    North Wales PA
    Running control and power in the same conduit is a big no-no. For many reasons, (heat, sharp object, etc) the two may become one and the results are very bad.
     
  5. jerekb

    jerekb Member

    Messages:
    69
    Likes Received:
    2
    Location:
    Woodland Park/Aurora, CO
    So is this illegal in the US?
     
  6. cdub260

    cdub260 CBMod CB Mods

    Messages:
    1,304
    Likes Received:
    151
    Location:
    Southern California
    Yes, it is. I don't have my code book in front of me right now, but running high voltage and low voltage in the same conduit, or even through the same junction box is a clear violation of NEC rules.
     
    jerekb and (deleted member) like this.
  7. jerekb

    jerekb Member

    Messages:
    69
    Likes Received:
    2
    Location:
    Woodland Park/Aurora, CO
    Oh crap well that kinda ruined my plans. Oh well no biggie I'll have to just look at a new way or running the cable. Thank you all.
     
  8. Dionysus

    Dionysus Well-Known Member

    Messages:
    1,098
    Likes Received:
    179
    Occupation:
    Technical Director
    Location:
    London, Ontario, Canada
    Yes it is VERY illegal I think pretty much anywhere to run "line voltage" or "high voltage" in the same conduit as communications or low voltage wiring.

    If possible you can always put another conduit beside the existing one and it's all fine. The conduit will also help shield.

    I can give you the CEC code rules, not not the US.

    12-904(2) & 60-308 are the primary rules that jump directly to mind.
     
  9. Chris15

    Chris15 CBMod CB Mods Premium Member

    Messages:
    4,140
    Likes Received:
    416
    Location:
    Sydney, Australia
    I will note that there are actually ways and means of doing it legally under Australian rules. One involves running the comms cable within a subconduit. There is also a specific exemption that relates to LV cable used for BMS (Building Management System) purposes.

    Depending on your install, you could possibly get away withcable tying the DMX line to the conduit...
     
  10. cdub260

    cdub260 CBMod CB Mods

    Messages:
    1,304
    Likes Received:
    151
    Location:
    Southern California
    In Australia, maybe. Not in the U.S.
     
  11. Chris15

    Chris15 CBMod CB Mods Premium Member

    Messages:
    4,140
    Likes Received:
    416
    Location:
    Sydney, Australia
    OK, so let's all agree that for 95% of people and in 95% of situations it's illegal. If you don't know the code references that permit it, then I would suggest that they do not apply. In pretty well all cases, school situations won't be under the exemptions.

    Actually, I retract the comment about cable tying it to the conduit also. If we are to call the DMX cable a telecomms cable, then under Clause 8.2.1 of AS?ACIF S009:2006, that would constitute an attachment to another service and be frowned upon.

    If anyone wants to get academic, I don't mind and we can throw code references around...
     
    Last edited: Apr 2, 2009

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice