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LX Bars

Discussion in 'Lighting and Electrics' started by Thomas, Jan 8, 2007.

  1. Thomas

    Thomas Member

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    So, this might be a bit of a strange question, but all of the LX bars I have used are generally made of some sort of metal; either painted black or left as-is, but nonetheless metal. In the event of, say, a janus shorting (the kind you get when crazy tech students make them for you) out against the pipe, the I'd assume the current would electrically charge the bar and all hell would break loose- has this happened to anyone?
     
  2. fredthe

    fredthe Active Member

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    Um... that's the point of having a proper ground connection on every instrument... to protect from this happening.

    If you're putting up homebrew equipment, without proper grounding, I hope you have good insurance coverage :)
     
  3. zac850

    zac850 Well-Known Member

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    And I hope your insurance company doesn't figure out that everything in the grid was ungrounded.

    Otherwise, yes, grounds should exist. And don't have people you don't trust wire your cables.
     
  4. Van

    Van CBMod CB Mods Premium Member

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    a Janus ? Is that a Two-fer ?
     
  5. TechiGoz

    TechiGoz Active Member

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    If you are hanging home-made fixtures (as others have said) they should be properly grounded otherwise there is the risk of having 'all hell break loose' and the bar becoming charged. This would be a bad thing, and the insurance companies generally tend to look into detail into cases like that..
     
  6. Chris15

    Chris15 CBMod CB Mods Premium Member

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    Are not most lighting bars suspended by metal and that metal in some way earthed? Eg. with a steel grid or a proper earth wire? This should be stopping the bar from getting charged shouldn't it? Or am I on a different wavelength?
     
  7. Thomas

    Thomas Member

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    Ok good, bars are earthed so any short will hit the ground and go away.
    Janus is an extension cable? Like a 5m run of cable to give you some distance between a wall plug and a fixture? What do other people call this? Industry standard down here..?
     
  8. Van

    Van CBMod CB Mods Premium Member

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    Oh ok I thought, Janus = Two faced God and translated that to Janus = two-fer < one male----> two females. > ( the french have another word for that > Maybe Janus started out as a trade name ? Like Crescent Wrench.
    Just another one to file under the interesting Nomenclature file. BTW a 5m cable in the Cinematic world would be a "stinger"



    As to the "Earthing" < grounding here in the states> Just because the grid and LX bars have a path to ground doesn't mean you can't get a buzz from them. All cables and All fixtures must be properly maintained and Grounded < earthed> to maitain the safety/integrity of the electrical system asa hole. Remember pipes, clamps, Cheeseboroughs, all get paint and oxidation build up on them. The human body makes a much better/shorter path to ground. Just because the grid is grounded you cannot count on that to reduce your risk of shock. If The students don't know how to build cables, then they need to be shown how. if they are rushing and not doing a proper job of it then they need to be shot. Or at least have the importance of what they are doing impressed upon them. Wiring is something that is done just to make light happen it is a life/safety issue for the public and everyone who walks through the doors of your theatre.
    Ok now I'm done.
     
    Last edited: Jan 10, 2007
  9. Chris15

    Chris15 CBMod CB Mods Premium Member

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    Hmm, never heard of these terms "Janus" and "Stinger" in this context. I shall have to do the same as Van and file them in the synonyms file.

    Here we just call them extension leads, whatever their length, boring I know.

    As far as grounding goes, Van, you are right, I stupidly made an assumption (must have been late at night). Is it not standard practice to run a wire to electrically link the LX Bar to the building's electrical system Earth?

    As far as wiring, I am slightly surprised that the school's insurers etc. do not have a major objection to you doing your own wiring. Ignoring that, it would be a good habit to get into the practice of properly testing cables that have been finished before putting them into service. Down here, you are required to do so, not just when they are new, but regularly (every 3 months in most cases) as part of test and tag, which not only tests for basic wiring errors, but also tests the resistance of the earth bond and the insulation resistance as well as other tests for appliances - ask if you want more boring details.

    While I understand that you probably are having students build the cables as a learning exercise, perhaps something other than mains would be better for this? Otherwise, keep a close watch and check the wiring thoroughly before the backshells go on - easier to correct mistakes then

    Just my thoughts, take em or leave em.
     
  10. Van

    Van CBMod CB Mods Premium Member

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    Chris, as far as grounding/earthing the grid itself goes, out of the 5 < standard pipe grids > I have installed, none have had a direct tie-in to the grounding/earthing system of the buildings electrical system. To the contrary most are pretty well insulated from anything because of the use of rubber installed around all connetions to reduce noises like squeaks of metal on metal.
     
  11. Chris15

    Chris15 CBMod CB Mods Premium Member

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    Well can I then take a slice of humble pie and stand corrected?

    My thinking had to do with the metal being tied into the Earth of the power cables feeding onto it - be it through multicore cabling or anything else. But it was all based on speculation and perceived logic... that probably was the first mistake ;)
     
  12. ship

    ship Senior Team Emeritus Premium Member

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    LX bars could mean a number of things to me at least. Could mean the pipe that fixtures are hung on, or a lamp bar that has fixtures permanently mounted to it and wired to it, and that bar gets wired often to a multi-cable fitting so as to power up all individually.

    Both often have a similar concept in what’s a grounded fixture is a grounded pipe. Not such a good concept by way of loose bolts, paint blocking conductance and other stuff - path of least resistance could be you.

    In the past and of un-grounded systems, one might find these very questionable load rated isolator rigging balls rigged in the fly system somewhere between the pipe and cables supporting it. Such isolator balls had no other purpose than isolating the wire rope of the fly system from any shorts now applied and welding it together in an un-safe way. You won’t find such things on the market these days - defiant doubtful load rating by way of how often they need replacement much less what their actual load rating was. Anyone else seen such things on a fly system - sort of like a swivel with a 3" ball of material between eyelets?

    Anyway, these days, on a fly system at least, it’s code and or good practice that the electrical drop box or gutter is mechanically by way of the box if not the pipe also grounded - this as with on a static grid and or pipe that it’s also grounded supplemental to any fixture grounding practice.

    In a lamp bar, that’s a different thing. This concept of a pipe with fixtures semi-permanently mounted to it only requires one safety cable given it’s now one unit - often of four or six fixtures, which are assumed not in concept of safety in ability to come loose due to improper mounting. One safety cable per lamp bar is sufficient.

    Lamp bars are fraught with design issues - both the code compliant ones and those more home made. Defiantly not something to be having students make without direct supervision. All realistically if they have conductors or splices within, should be properly grounded and not rely upon fixtures mounted to them to do so. Imagine if one will you have a six circuit lamp bar and a pig-tail attached to it. Pig-tail meaning fan-in or series of plugs attached to say a multi-pin plug which the bar accepts. In any case of the six circuits, you have only #1 plugged in and with lamp working, #6 is also plugged in but it’s lamp is not and somewhere in the cable feeding #6, there is a short. It’s a question of resistance to ground if you in touching the bar are a better path to ground than what bolting method #1 has to the yoke, than yoke to ground screw and wire. Lots of ways one can find a un-grounded or high resistance short within a lamp bar. Best to ground the lamp bar itself given this. Ground everything in fact.

    Get the idea here of wee problems in grounding a lamp bar proper? This beyond it being against code to have a fixture supporting bar that also has current carrying cable running thru it. Against code in reality to do a pipe that both bolts fixtures to the bar and has those bolts passing by the conductors feeding the fixtures. Gee, all it takes is one conductor nicked by a bolt... makes sense. TMB to the best of my knowledge is the only company that has a compartmentalized lamp bar and they use a Unistrut system which is also not so good by way of how them bolts secure in a permanent = not able to come loose sort of way. This short of threaded stud Unistrut nuts and side lock nuts as a theory but not much of a ½ twist to be loose and falling concept. The TMB bar complies as most don’t with the NEC in separate pathway for conductors than support of fixture, but doesn’t by way of each individual fixture being a part of the bar and unique. Were it my choice, each fixture on such a bar would require a safety cable. Given it is my choice... this might become the case.

    None the less, conductors feeding the bar - bad thing when thru bolting the bar to a more safely rigged fixture yoke. This given good crimping and splicing. Leko department normally takes care of all them bars that in the past or in the field had someone using an other than insulation displacement crimp tool on the crimps of a lamp bar. Smashing the crimp only holds conductors as long as they maintain their original shape while being smashed into conducting. Vibration and heat tend to make wire move about and or move under expansion thus settle. This causes resistance thus melting and or wires coming loose from a crimp especially if the fixture cable were twisted about a yoke and attempering to make that yoke twist just a bit more, made the fixture whip pull free from it’s crimp. Ah’ good crimps, both a question of proper crimp pressure and insulation displacement tool as opposed to insulation crushing tool.

    None the less, all lamp bars if proper fixture in one unit should be grounded but it’s a grey area. I ground my lamp bars - but only those I re-wire in having insulated the bolts from the conductors. It’s a concept in terminating all circuits of fixture ground to the pipe, than taking that in common ground of the pipe to the cable or plug that feeds that pipe so all lights are in common grounded and the pipe is also specifically grounded to all circuits.

    Finally on the subject of “black” black oxide coated bolts don’t conduct well. If relying upon a black oxide coated bolt such as on a C-Clamp, try not to there is resistance to factor in.
     
  13. Van

    Van CBMod CB Mods Premium Member

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    Hey Chris I think I like the taste of humble pie I seem to be eating it all the time. :mrgreen:
     
  14. Chris15

    Chris15 CBMod CB Mods Premium Member

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    You and me both...
     

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