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Electric Batten Multi-Cables Failing

Discussion in 'Safety' started by Toul, Jul 14, 2004.

  1. Toul

    Toul Member

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    About a year back there was an instrument dark on one of our electric battens. We flew the pipe in to re-lamp the fresnel, and when it got to ground level, the instrument was lighting again. We flew the pipe back out, and the light went out again. At a level of about ten feet above the stage (and well below show trim), the light switched over. We tried plugging different instruments into the offending circuit, and every time, the lights went dark at ten feet. At that point, that particular circuit was the only one that behaved in this manner. Unfortunately, the batten was completely full of fixtures, and there were no free circuits on it, so we ended up sacrificing worklight for part of our green wash.

    A few weeks later, another circuit on the same pipe went out in the same creative way. This time there wasn't anything non-crucial to lose, so we had to twofer a pair of spotlights that generally came on at the same level to free up a circuit.

    Then it happened again. This was when we started wondering about why this was happening. The only thing that really changes while the electric flies in and out is the orientation of a pair of multi-cables that run up to the cieling in a sort of loop. Those with electric battens probably know what I'm talking about. The only thing we could think of is that the multi-cable was somehow getting kinked and pinching off one of the circuits inside it.

    We called an electrician, and he confirmed our assessment. There are apparently some extra circuits in the multi-cable, though, and he went ahead and used the extras to give us our non-functioning circuits back. He warned that there was only one extra remaining, though, and that this was likely to keep happening. Sure enough, we've lost two more circuits in the time since he fixed them. Since this happened on our most crowded pipe (directly above the apron), we needed to run power some other way. Our solution was to take four ordinary extension cables from floor level all the way up to the cieling where the multi-cable terminates, then running them parallel with the multi-cable to the end of the batten. From there, more extension cables can take power to the instruments where we need them. At this point, it's our only workable solution.

    My question is whether anyone else has heard of a power multi-cable failing like this? I figure if they're used in that kind of application, they should be designed to flex and bend at least a little bit.
     
  2. mbenonis

    mbenonis Wireless Guy Administrator

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    Well, I've never seen something like this happen at our school. However, it makes me nervous to know that random electrical circuits are being "pinched off" at any given time. Depending on the age of the installation, I would recommend trying to get whomever installed the lighting to come out and fix it, or if this is not a workable solution, save up the money and get it fixed. It's only a matter of time before more circuits go - and it may also be a fire hazard (although only a licensed electrician can make this judgment).
     
  3. ship

    ship Senior Team Emeritus Premium Member

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    Agreed that's probably the best thing to do and ASAP because such things grow worse not better. No doubt a loose wire in a terminal somewhere or bad crimp and easy and cheap to fix. On the other hand somethig not to play around with.
     
  4. Mayhem

    Mayhem Senior Team Emeritus Premium Member

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    Was or is there any sharp bends or kinks or even a point at which the wire is pulled tight or stretched?

    Most cable will work fine if supported and allowed to bend in a radius that is not too extreme for that particular cable.

    I have seen cables fail because they have been flexed too much, causing one or more of the conductors to break.

    Nothing last forever and depending upon the age of the cable and the treatment that is receives, the life of the cable may be shortened.

    Some people believe that once a cable is installed and working that is it. However, I would suggest inspecting moving installed cables. There is always a possibility that it will get kinked or pinched in travel.

    I hope that this helps and also alleviates concern that all multicore cable will fail. Yes - eventually it will but if kept in good condition you should be able to keep it in service for a decent amount of time.

    Another thing that I refuse to do is fly cable without using a wire rope from which to support it. Stretching cable whilst running a load through it is just asking for trouble in my book.
     
  5. Toul

    Toul Member

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    The cable has been installed for just under six years now. JT, the tech guru at my school, has been in contact with the original installer and with a third-party electrician (whose visit I described). From the noises these people are making, it seems like it will take quite a lot of money to fix.

    The cable is properly supported. There is a type of cradle that the cable takes a turn through on its way to the stage, and the cradle moves up and down with the batten. If I had a photo I would post it so you could see it, because it's hard to explain. There aren't any particular stress points anywhere along the cable: it moves pretty smoothly through its range. There's no real way to tell whether the wires inside are being stretched, because the whole cable is wrapped in 3/8" rubber sheathing.

    I understand that all cable eventually fails, but a six-year-old cable should not, since it's been properly used for its operational life.
     
  6. Calc

    Calc Active Member

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    At my high school, we had the same problem. Our lighting system was thirty years old at that point (the system was installed in '73), so we weren't really that surprised that things were beginning to go wrong. The entire electrcal system needs to be re-done, and that's not going to happen anytime soon. The solution that we found was to tape the multi-cable to the batton in a position where it will still work.

    I'm not recomending this over a full replacement, but it worked for us.

    Boy, i'm glad I got out of there when I did. The house lights no longer dim, so they have to use the main breakers to turn them off. They need the whole electrical system redone, but at $180 grand, that won't be soon. At least they just finished the $80 grand sound system (with money left-over from the football stadium restoration, of course).
     
  7. Toul

    Toul Member

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    You don't know how comforting it is to know that someone else has had the same problem. Although it is disturbing to me that yours was thirty years old at the time, and ours is only six. A full replacement of the cable might be in our future, especially if dimmers continue to fail. Thanks for letting me know I'm not the only one!
     
  8. Toul

    Toul Member

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    Yes. Plenty of slack.
    Within the cable. Both ends are firmly secured into electrical boxes, one on the batten and one hanging on the wall in the catwalks.
     
  9. ship

    ship Senior Team Emeritus Premium Member

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    In addition to Ron’s very appropriate strain relief and support questions:
    Part of the bane of my existence at work is my ability to fix at times ten year old 16/7 cable feeding chain hoists. Hmm, 16/7, that’s about 3 and a half all be it heavy duty zip cords being tugged on at times by a two ton capacity chain hoist if snagged. What’s going to give out first a single wire in the conductor especially those at the center of the wire where other’s outside of it at 1/4 twist per foot have a lot more wire to them to stretch out with than those at the center which for the most part are straight, or the 4,000# capacity chain hoist being fed by it? Often there are some conductors beyond a ground at the center core of the cable you are using and they will once the cable stretches out need some repair due to their shorter length.

    Wire Rope User’s Manual gives a specific formula for where a piece of wire rope or in this case in being similar electrical cord when used under the same conditions will give out. How many pounds of counterweight do you have on the electric’s arbor verses even at the required 10ga cable, what’s it’s strength per conductor? Possible than that one single wire just could not resist the weight and even if it works at times in one position, that does not mean it’s safe to use. Wire once pulled apart has some strands that stretch or break at different lengths than others thus it’s not a clean break. You might get a few strands of wire that in some positions still have continuity but in others are pulled apart. In any case, those strands of wire in comparison to the amount of strands which will never touch are not given the loose interpretation of connection, much less conductor size able to carry a load and will have a lot of resistance to them - at times sufficient resistance to provide a fire or melt the insulation between opposing phase conductors. This in addition to wires that were never really tight enough at screw terminals by simple mistake, wires that were not crimped hard enough to resist pulling out of the ring terminal and a multitude of other reasons for a failure of the cable. Used to work for a theater that still was using it’s original 1926 drop cable. Grounding the stuff was more a concept in creativity and spare time than reality, but the stuff still even today still no doubt carries it’s design loading in amperage without problems. Six months later, three years later, the cables involved are designed to function to design many more years than that. Often especially if a issue with the cable itself, it’s going to be a lifetime warranty. That Soco cable I spoke of a month later I was contacted by the vendor about in offering to both pay for shipping it back and direct replacement of no matter what the actual cause of the problem. All their cable has a lifetime warranty on it. Many multi cable types have similar warranties but labor given an installation does not. The longer you wait to get it fixed, the less chance it’s warranty much less you will have pull with the installer. Maintenance being one thing, the idea that someone might make a mistake and plug such problem lines in no matter how well marked could be a fire or more expensive problem. Could be a defect in the cable, while doubtful and more likely a simple and easy to fix repair in the box - given qualified to be in the box.
     
  10. Toul

    Toul Member

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    Ship: I appreciate the effort, but the truth is that almost everything in that last post went over my head. 16/7 cable? Chain hoist? Zip cords? Nothing like ControlBooth.com to show one how little one actually knows.

    However, I was able to come up with answers for Mr. Hebbard.

    It's operated automatically. The pick (I didn't know the name for it; always called it the cradle) is suspended from a lift line just like the batten, and moves in tandem with it.

    The cable runs through and is strapped in somehow. I don't remember exactly, and I won't be back in the theatre till school starts in late August.

    I don't know what Kellums grips are, but I know that the pick is a semicircular metal deal. It turns the cable with a radius of about 8".

    I've never seen the inside of either electrical box, but I know that the cable goes in and is supported by some sort of wire mesh wraps around the cable for about 36" to ensure it goes into the box at a right angle.

    Primary strain relief...? Is it the wire mesh thing I mentioned? I don't know quite what you mean.

    Exactly the same way as on the wall.

    I don't know; I've never looked inside. The electrician who visited us did, though, I think, and didn't find any problems except that a few of the circuits were dead.

    And no, it definitely isn't being flown many times every day. The worst we do to it is an occasional bounce focus when it's impossible to access with a ladder, and that's five times in and out, at the most, in one day. But most days it stays right at trim without moving. That's the vast majority of the time.

    It may have served well to mention this earlier, but the batten is not part of a conventional flying system. It's what we call our "apron electric" pipe, and it's farther downstage than our first real lineset, actually in front of the proscenium walls. It's operated with an electrical winch from floor level. The motor pulls four lift lines on the batten (which is shorter than a conventional batten, since it doesn't need to stretch off into the wings) and one on what I've learned is called the pick. There is no counterweight; it's moved by sheer electrical muscle. I didn't see how any of this was relevant in the beginning (and I still don't), but now I'm more confused about this than I was to begin with, and I figured I'd go ahead and give you the whole story, in case someone can figure out what's going on.
     
  11. ship

    ship Senior Team Emeritus Premium Member

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    My apologies for going over your head. Print this stuff than present it as questions to the next visit by the electrician - hopefully soon. Might be of help in figuring out the problems in either of our cases.

    In my post the 16/7 and zip cord was a similar reference to what might be your problem about the effects of what happens inside of a cable when tugged on by a large enough source of weight or tension.

    How little one knows, to a certain point perhaps, I know what a Kellem's grip is but 10 years ago will not have either. Stuff once you hear of it to study and larn about instead of being intimidated by it or feeling small. In the end we will all have our specific specializations above general knowledge. Once a few people bang their heads together with many opposing ideas much less experiences, you get a wealth of information.
     
  12. Toul

    Toul Member

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    No apology necessary. It's exciting to encounter people who know things I don't. It convinces me that there is more to learn, and I love to learn things.

    Someone (Brian Desmond) e-mailed me some definitions a few days ago of the things I was having trouble with, and they helped a lot. He said he would try to remember to post them here, but I think I might as well do it for him, for the sake of anyone out there watching this thread and wondering the same things as I did.

    That being said, I still have no idea why my cable is failing. :eek:
     
  13. Mayhem

    Mayhem Senior Team Emeritus Premium Member

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    Just a quick thought, although as I am not familiar with the US systems, it may not be a valid one. (The reference to zip cable has me questioning my thoughts somewhat and I remember reading somewhere that some of your fixtures/plugs do not carry an earth).

    I would assume (based on what we do) that in addition to active a neutral feeds to the electric batten, you would also have an earth feed. I would also expect that the batten itself is earthed.

    Now, if you lose an active or a neutral, you are alerted to the problem (as in this topic) because what ever is running off of the broken/failing wire ceases to work. However, how do you know if the earth fails?

    As routine, I check the continuity and insulation of all my power cables every 12 months and a cable will also get the once-over if it has been damaged, or demonstrates faults. I have had several IEC leads (factory pressed) that have come with equipment that have had faulty earths.

    So, all of this got me thinking as to whether or not your electrician has checked the earth on this batten when checking/repairing the faults discussed in this post.

    Also, are my assumptions in this post correct?
     
  14. Mayhem

    Mayhem Senior Team Emeritus Premium Member

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    Thanks Ron, Glad to see you are still out there. So, what you are saying is that the electric battens are not earthed then?

    Cheers,
     
  15. Toul

    Toul Member

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    It's funny to hear the Australian terms for things. Instead of "earth" we use "ground" here, and there are ground wires running to every instrument in the plot. It is true that in residential electrics, we often don't use any ground. An edison outlet in a home has three holes, but many appliances only have two pins. However, for theatrical lighting, all instruments use ground pins, no matter what the plugging system (we use twistlock).

    And so you're right: the ground wires could be failing within the multicable and we wouldn't even know it. This is a scary situation for that reason (and many others), and possibly all the more urgent for it. I wish I'd gotten a chance to speak with the electrician when he was here, but I was unable to. I'm assuming that if he was worth his multi-meter, he would have checked everything out, including the ground wires. However, too often such professionals do slip up in elementary ways. (Slightly unrelated, but once I had a painter come to paint a room and he didn't remove or mask the doorknobs and outlet covers before painting, so they were painted at the edges when he was done. He didn't get paid in full for that job.)

    I won't be back in the theatre till mid-August, but this will be a priority when I get there. I would hate for something bad to happen.
     
  16. ship

    ship Senior Team Emeritus Premium Member

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    Easy enough to check ground if you have a Gam Check. Granted such things are very expensive now but well worth the investment as long as it's stored in a locked up place. Those tech people with lots of cash would not go wrong to invest in one either.

    In a bundle of multi-cable and very dependant upon who circuited which what where, often the grounds will be at the center of the bundle and break first given the inner conductors are shorter once the cable stretches out, along with any conductors also at the center of the multi-cable. You had never mentioned which specific circuits are failing but I would assume them to be if wired as per the Soco standard wiring, that the inner conductors would be first ground than wires feeding circuits of larger numbers. A work light would afterall normally be installed at the end of the circuits avalable. This is given they did not wire it wires 1-3 Hot/Neutral/Ground instead of Hot/Neutral, Hot/Neutral with grounds in the center of the bundle.

    I also wonder about the comment of extra circuits still available. Given the cost of multi-cable, I would think it somewhat rare that someone would invest in a cable with as described three extra circuits not used since it will not have been much more of an investment to make such extra circuits live.

    This would go into the question of what or how these extra circuits are found. Are extra circuits coming from shared neutrals which would be a bad thing, or sharing grounding conductors which can be fine if done right.

    Inside the box, it's very possible that given a 12 circuit drop box, that all grounding conductors go to a single grounding bar than split off to individual circuits. This would both ground the box and allow for the extra circuits once you leave the assumed necessity of one wire per ground and it's bridged/bonded on each end of the circuit. In reality you don't need one grounding conductor per circuit when they are bonded together. What's the chance that all 12 circuits will short at the same time thus overload the grounding conductors? For this reason, many Soco type cables only use two grounding conductors. This given someone was not working on the Lekos and decided that the Mica insulator was not necessary within a S-4 Leko lamp base.

    Another good tool to buy would be a Fluke AC-1 voltage sniffer. Very useful and the size of a marker. In this case while other companies produce similar voltage sniffers, trust the Fluke at the extra price - sensing voltage means your life. Put your sniffer up to the drop box and see if it detects a voltage - it should not. This would definately indicate when those bad circuits were powered up that some wires were flopping around inside of the box and dangerous. Something to check out of safety. This given such circuits that have come loose are touching the box and energizing the entire lighting pipe.

    Given this is the case, and especially that the drop box is bonded to the ground circuits, it's very unlikely that you have circuits without a ground unless what's left of all grounding wires also break. Again the Gam Check would show this. It could be that if the wires were fed directly to the circuits without direct bonding/grounding strip that the plug itself is forming what's called a mechanical ground to a working ground of another circuit in metal to metal contact of plug to plug by way of metal box thus short of opening up the box to see what's happening presence of a ground or not won't tell you much.

    Given all wire mesh strain relief (Kellems Grips) are in good condition with no un-jacketed cable coming out of the box and the wire mesh not digging into the wire too deeply. Much less as Ron earlier described that the cord was at some point shorter than the fly system's cable thus the cable at some point was too short and became a substitute for the wire rope in being pulled to an extreme with the weight of the lighting pipe. In other words, when the cable feeding the electric gets hung up or the pipe is flown in llower than the cable will allow, it tends to stretch that feeder cable because it is supporting the weight of all lights and pipe on that electric.

    Once this happens, wires in the cable - especially the center core conductors (my zip cord refrence) can break, much less with the straign, wires can be pulled out of their crimp terminals given the strain relief fails in picking up the strain of holding up an electrics pipe.

    I would think that as long as the drop box is de-energized completely, you would be within your ability to open up the box and look for wires pulled out of their crimp terminals. This than would by way of observation in not touching anything allow you to see any wires that have pulled out of the terminals. A slight tug on problematic circuits will also either show wires with intermittent contact inside of the box itself verses those wires with a good connection. Given said crossing out of wires inside of the box - both the box in the grid and on the pipe, this would show if it's a simple crimped terminal problem verses something in the cable itself. Also while in the box, looking at the wires coming from the strain relief which are giving problems should have some amount of slack to them in the box. If there is no slack this would mean the center core conductors or other ones have problems in the cable in having slipped. A good indication of broken wires.

    Given 10ga as the standard for drop lines, even a six circuit set of wires at that wire gauge should be sufficient to hold the lights on a pipe for a time. Given this, I would first suspect a crimped terminal within the box.
     
  17. ship

    ship Senior Team Emeritus Premium Member

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    Darned error messages and double posts!
     
  18. Toul

    Toul Member

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    I recall our tech director mentioning that the electrician said the failing circuits were those on the outside of the bundle. I can tell you for sure that circuits 1-16 serve that pipe, and the failed circuits were 3, 5, and 6, at the opposite end of the pipe from the electrical box and multicable.

    The Kellems grips are in good condition, and the rubber sheathing is intact. There is plenty of slack in the cable run. Nothing I can think of is making this cable fail.

    I can see right through you. This was just an underhanded attempt to increase your post count. I'm onto you, ship.
     
  19. gremlin1287

    gremlin1287 Member

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    OMG...It sounds like you're having the exact same problem my school is having...when flown in the circuit works but once it reaches ten ft. or so., it just turns off...the building is a little more than 5 yrs old...what we're going to do is, since we actually have enough multicable left over from the original instalation, we're going to have the people who installed our electrics come in and run a new multicable...we'll be saving money because we already have the multicable...heck we'd do it ourselves if it weren't for the fact that custom wiring without proper training is a bad idea.
     
  20. ship

    ship Senior Team Emeritus Premium Member

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    Remember howerver that in replacing the circuit with a problem that in the future someone might see this circuit and intend to work with it, plus given it’s only a few years it might still be warrantied if not a simple fix. While installing another line might be useful, those stringing it should also check the circuit to see if at least it’s something simple that went wrong. Power on occasionally for the most part normally is cable related but can also be an easy fix once you find the occasional contact break in the wire. If it’s not fixed and left in place it can be very dangerous not just in occasionally working but when it is working, it’s a high resistance connection and can cause a melt down of other circuits.
     

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