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Melting Twistlocks

Discussion in 'Lighting and Electrics' started by BenjaminD, May 23, 2007.

  1. BenjaminD

    BenjaminD Member

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    My highschool auditorium hasn't been maintained in a while, and we have a bunch of twistlock sockets (on pigtails) melted to the plugs in them. Have any of you encountered this problem before?
    Why does this happen? Is this just a case of Abused 20 Year Old High School Auditorium Syndrome, or is it something I can prevent?
    What is the best way to fix this (I have been using a hammer and destroying the connectors too damaged to open).
    Ben
     
  2. Jezza

    Jezza Active Member

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    If you don't actually "twist and lock" the connector, you can inadvertently create an arc between the barely connected pins inside the connector which will melt the connector.

    Also, if you overload the connector over 20A, your breakers should trip, but if for some reason they don't, the connector might be the next place to release the energy.

    I wouldn't be taking a hammer to the connectors. Just doesn't sound like a good idea. I would attempt to unscrew the twist and lock from the cable if possible and remove it that way, or cut the pigtail and put on a new connector. Unless your fixtures are twist and lock as well, put on female stage pin connectors on and make your life easier.
     
  3. soundman

    soundman Well-Known Member

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    Something is very wrong if the plugs have melted together. It could be casued by several things not limited to pulling more amps through them then they are rated for or a loose conection that has caused some arcing. If it were my space I would pull the dimmers for the affected circuts and cut the pig tails. If there was enough heat to melt the plastic plugs there is a fair chance that the insulation is shot. Replacing the pig tails completly would be best.
     
  4. soundlight

    soundlight Well-Known Member

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    I had some of those at my HS. They were on the sockets that I was running 1800W through, and I think that (even though the cable and connectors were rated for above what I was pumping through them) there was some sort of short inside the connector due to lousy wiring that melted the plastic.
     
  5. BenjaminD

    BenjaminD Member

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    Jezza: The connectors are too badly melted to unscrew. That's part of the problem. The socket and plug are melted together, and they're both melted enough that I can't undo them without a hammer. I have no idea if they were locked, originally... they were probably hung over 10-15 years ago (there is enough dust on the fixtures to grow a small garden. I'm cleaning them... slowly....

    Everything in my theatre is twistlock. I wish we had stagepin, but we just... don't.

    soundman: Due to the fuses on the dimmer (never blowing) vs the rating of the plugs, I don't think they could draw enough power to melt the connector. Actually, it might be a loose connection... except that I've found 6 connections melted together. It's possible that a previous TD didn't understand the concept of twistlock, but unlikely.

    I'm scared/worried about this because it creates sparks (like when you hot-plug a fixture, except they don't go away. I caught one doing it today, I noticed the fixture behaving erratically, and went down to check it out, and discovered the connector was buzzing and occasionally sparking. And the screws holding the connector together were slightly charged(!). I flipped out, of course, (and replaced the plug and socket) but what if I hadn't noticed?

    And how on earth can you replace a pigtail without removing the entire electric/batten assembly?!

    soundlight: most of these channels are for striplights, not loaded over a KW... Again, I'm not sure of the intelligence of previous electricians/TD's/random people that would install plugs
     
  6. icewolf08

    icewolf08 CBMod CB Mods

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    It sounds to me like what you need to do is check every plug on every fixture and every plug-in strip/raceway. Make sure that all of the wiring is attached securely and correctly to each connector, and replace any that have any signs of damage (chips, cracks, charring, scorches, etc.). This could turn out to be a costly and time consuming project, but it will be totally worth it, not to mention that it is a safety issue.
     
  7. rmarston

    rmarston Member

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    Been using twist locks forever - no problems. Souinds to me like an impedance problem in the connect / plug - that is if they are not being loaded beyond their rating. I bet there is loose connections on one or both sides of the connection - resulting in meltdown.
     
  8. Charc

    Charc Well-Known Member

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    Edit:

    Read Ship's post, next page.
     
    Last edited: May 24, 2007
  9. icewolf08

    icewolf08 CBMod CB Mods

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    Twist lock connectors are not unsafe (when installed correctly). The Key-Out twist lock connectors (I always forget the code numbers) are not supported under the NEC as I understand it, but the Key-In connectors are NEC compliant. I wouldn't quote me on this, but I believe that is true. There are still many theatre that use both kinds of twist lock connectors, and there is no reason to change everything to stage pin if you can fix/replace parts with the same connectors.

    ADDITION:
    Key-IN Twist Lock: L5-20 is NEMA compliant. below is a photo of one from altman:
    [​IMG]

    Key-OUT Twist Lock: non NEMA compliant. below is a photo from altman:
    [​IMG]
     
    Last edited: May 23, 2007
  10. Edrick

    Edrick Well-Known Member Premium Member

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    Being that your theater isn't anchient but it isn't brand new what is some of the equiptment you have for lighting and sound? Being that I'm the first person to go through the first year at our new high school I can only wonder how it will be 20+ years from now.
     
  11. BenjaminD

    BenjaminD Member

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    I'd love to go all stage pin, but I simply don't have the funds. This year was the first year we had any kind of budget, a grand total of fifty entire dollars. I can beg the school to get me lamps and they usually will. Other than that, I really don't know. And when I do start bringing up saftey issues, our flysystem is first on the list. We do use the key-in connectors, and they should be (and have been) alright except for a few that, apparently, were installed/connected incompetently... resulting in unsafe conditions.

    But I'm glad to hear that this isn't "normal," and that this problem could be alleviated if I checked every single plug and outlet for correct wiring and made sure they got a good connection every time.

    Rickblu: I have a strand 300 board (24/96), and two strand CD80SV racks. I have about thirty very old strand lekolites, 16 or so strand 6" (750 watt) fresnelights, and 8 or so 8" (2 KW) strand fresnelights, and four 3 circuit/12 cell strand strips, and four 4 circuit/12 cell strand strips. Oh, and 8 2-cell cyc wash units that look far better pointing at the stage than the cyc. Our real problem is drapes... they look atrocious. Sound, we have 2 QSC 1000 watt-per-channel stereo amps, and an old 24 channel mackie mixer. Most of our mics decided to walk off (before I go there), we have one corded and one wireless SM 58 and a bunch (5?) of strange audio-technica handhelds with rather disgusting pickup pickups. I have no clue what the mains speakers are, due to the nasty fact that you need a full body harness to get to them safely and I'm not stupid enough to think that I can use a rope to climb down onto the ceiling surface that couldn't support me anyway (annoying!!) Our booth monitors are driven by a Crown 200 WPC amp, but they're both dead and I replaced them with a very, very strange combination of speakers that actually produe decent sound. We have peavey 15" monitors (x4) driven by 500 WPC QSC amps. All in all, we're fairly well off. Excepting those times when you have to resolder half the com system to repair damages done by kids skipping in class, when used condoms fall from the loft (which I recently padlocked), or when plugs start to fuse together.
     
  12. ship

    ship Senior Team Emeritus Premium Member

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    He he he, about what was it 20 or 30 years ago were this a post, someone will have said twist lock as modern instead of stage pin. Twistlock is the “get into the current days” reality for when the theater was wired and there is absolutely nothing wrong with it. In fact, a twistlock stage has certain advantages over that of a stage pin stage including plugs not coming undone by way of gravity and experience in splitting the pins. This much less, experience in knowing how to wire a plug, it’s simpler to get a standard twist lock properly done than that of a stage pin that takes crimp terminals or ferrules properly applied and often not done properly.

    Sounds unsafe and planning a work stoppage ha? Time based upon your experience with real life to learn from it and make the best of it over avoiding it. On a personal note, did you ever study why stages at some point went twistlock, why it’s in many ways very safe and even if it were Edison plugged safe and code compliant? Before getting on a high horse about refusing to deal with what you get the chance to experience, understand it that fix it. Running away and stomping one’s foot don’t help.

    I would on twist lock plugs rely upon the rattle test of the plug. A twist lock or even Edison plug shouldn’t rattle when you shake it. You hear a rattle, you know some screw terminal is loose. This as opposed to stage pin plugs that have extra tolerances and do tend to rattle if you shake them, a twist plug won’t rattle if in as a broad concept safe condition.

    Follow this up with the why a plug might get hot. Imagine a bunch of strands of wire under load. That’s the theater aspect, now add the science aspect of expansion and contraction and you now at times get a wire loose within a plug. This looseness causes resistance to current flow which results in heat. Don’t worry - also happens at times on stage pin plugs, much less the reverse of this where by something is overly tight and it also causes resistance to current flow.

    Simple enough concepts I would expect overall. Simple enough to also inspect each time such a plug is used as opposed to on a stage pin plug where used that they would make noise in a rattle test at least after innitial install where the strands of wire settle down due to heating in often also making for stuff that gets loose with age. Overall sounds fine to me, just needs some TLC. Too bad in being a top talent you would refuse to come back until you get what you feel safe.

    I would recommend a thorough reading of Edward Gordan Craig for background in such concepts.


     
  13. SHARYNF

    SHARYNF Well-Known Member

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    Time and time again I see where people with very little experience look at something and immediately jump to the it's not safe, I'm not going to deal with it.
    Equipment needs to be maintained, and part of TECH in many cases is finding these problems and fixing them. Things break, get worn out or go bad, it is part of the system, it is part of things working and aging. It could be any number of things like Ship said or corrosion or somebody not properly twisting the connector. It is really pretty common.

    Sharyn
     
  14. BillESC

    BillESC Well-Known Member Premium Member

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    If it sounds like you have a cricket inside the connector.... it needs fixing.

    All to often this is a symptom of a loose compression fitting. Over time as Ship alluded to, the actual screw terminals of connectors loosen which raises impedence, causing arcing and hence heat. You would be well advised to annually inspect every connector and tighten the compression fittings.
     
  15. soundlight

    soundlight Well-Known Member

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    If only high schools had the budget and personnel to do that. If I had asked the school system's elec maintenance department at my HS, they'd probably laugh. "You want us to inspect over 200 connectors that are giving us (as the maintenance dept) no problems so far? Who are you kidding?"
     
  16. Lightingguy32

    Lightingguy32 Active Member

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    A good sampling during an annual maintenence call would be to disassemble and inspect about 2 conntectors per electric per 10 circuits. this way you get an idea if some one has been wiring something right or wrong and what kind of shape in general the connectors are in over that one electric or through out the whole theater. I tested this technique before and it yields results that are pretty accurate. (actually i kind of invented this method)
     
  17. soundman

    soundman Well-Known Member

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    I see no reason wh this can't be an in house job by the theatre students. Fixing cable will prep them for there first few years out in the real world.
     
  18. avkid

    avkid Not a New User Fight Leukemia

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    With proper supervision of course!
     
  19. BenjaminD

    BenjaminD Member

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    Rattle test? That sounds quite ingenious. And definitely less time consuming than taking apart every plug in the place. Especially if I too apart a plug every circuit or four.

    Sharynf: I agree, fixing broken things is a very, very major part of tech. Particularly unsafe broken things. If something sparks, it obviously needs to be fixed, immediately. I was merely wondering why it would happen and if it was normal.

    I will probably have time to check the outlets and plugs during the first week of the school year (teacher planning week)... But thank you all!
     
  20. Charc

    Charc Well-Known Member

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    Don't want to hijack this thread, but after my stupid post on the previous page (now edited over) I'll hang my head in shame and make a post here.

    I got a bunch of lengths of cable, with no ends (correct specs, this isn't extension cable from wal-mart.) and I got a bunch of SPC connectors. All this was left over from the renovations of the theater. I really want to make use of all this extra cable, but I'm hesitant to work on anything that'll have electricity flowing through it. What do you guys think about it?

    (Notes about myself. Not wired anything for the theater before. Have done some minor electronics projects before, but nothing of this caliber. Student.)
     

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