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What happened with this wiring?

Discussion in 'Lighting and Electrics' started by jordandare, May 14, 2019.

  1. MNicolai

    MNicolai Well-Known Member Fight Leukemia

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    I definitely wasn't saying sweep it under the rug; just warning that going nuclear because of a non-response is recipe for a short career AND might not even fix the problem. My point was that there are any number of options you can avail yourself of more productive solutions without burning down your career. You get a lot further by emailing SSRC for replacement strips or asking the original installer for a quick service call of which they will almost certainly deliver so long as you don't rip them a new one before you ask. Even just saying to your boss, "I talked to SSRC and they're sending the replacement part all I need is a maintenance electrician for a few minutes to take a look at this." They'll spend more time finding a parking spot than working on the raceway. Calling Channel 4 might get the problem solved but you will fall on your sword in the process and you'll have a hard time finding empathy from anyone afterward.
     
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  2. TimMc

    TimMc Well-Known Member

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    Sometimes the squeaky wheel gets greased, sometimes it just falls off.
     
  3. STEVETERRY

    STEVETERRY Well-Known Member

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    Unfortunately, you have bumped up against "you get what you pay for" when it comes to the type of terminal strip in use. These are very low cost (dare I say "crappy"?) strips, and the terminals tend to loosen and overheat over time. "Cold flow" of the copper conductors under pressure does not help.

    This is precisely why ETC uses Weidmuller "tension clamp" terminals in our wiring devices. In addition to being much easier to terminate, the constant tension of the clamp compensates for copper cold flow, and there is no screw to loosen.

    If you can convince those in charge that the terminals must be replaced (you cannot reuse terminals where the heat has burned off the plating), I suggest replacing them with tension clamp terminals to prevent a repeat of the current problem.

    And make no mistake, you have a potential serious fire hazard.

    ST
     
  4. Colin

    Colin Well-Known Member

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    If you dont replace all your terminals with better product as Steve describes (sounds like that's an uphill battle) add inspection to the facility's regular maintenance schedule (which should exist). I have 16x 4 circuit SSRC drop boxes and yes they are very clearly not the same build quality as the ETCs I've got, but that's no big deal to me so far because once a year I open all of both brands up to tighten the mesh grip strain reliefs that work loose, and I put a screwdriver on every terminal screw while I'm in there - sort of automatic for me whenever I have anything opened up for other work.
     
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  5. Chris Pflieger

    Chris Pflieger Well-Known Member

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    Those look like they're on a rail, so they can be changed out with about anything pretty quickly, without much skill.

    As to the other things, write up a list, type it out in order of severity / cost, i.e. replacing em lighting batteries at the top. Then submit that to your superiors. Don't expect everything to get solved, but also, you may want to do some of the leg work - like getting quotes for those batteries.
     
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  6. SS Minnow

    SS Minnow Member

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    I am noticing that the wires on the bottom of the terminal strip are a smaller gauge than those on the top, which to me is a little odd IMO. The bottom wires also appear to be a bit crispier than those on top. Is it possible that at one time there was a heavier load on the circuits that are damaged at some point? Say there may have been maybe 2 1k pars twofere'd or maybe even 3 plugged in on the baton? I have seen this on patchable dimmer racks where the patch leads melt down due to fixtures being twofere'd up in the rig and the smaller gauge patch leads cant handle the load. I do agree with the possibility of loose terminal screws. Just throwing it out there. Likely the terminal strip would need replacing as well as some trimming of the burnt wire to get it up to snuff...
     
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  7. DrewE

    DrewE Member

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    I think it's just different wire types, but not (obviously) different gauges. The bottom ones are 12 gauge, rated for 125C, apparently solid. The top ones do not have any markings I can see, but look to me like they're stranded and have noticeably thicker insulation, and so I might guess are broken out from a multiconductor flexible cable, which would of course also be standard practice for a stage electric. It is possible they are heavier gauge due to derating required for the cable; but at any rate, I have a hard time figuring how the bottom wires could be seriously overloaded assuming the use of 20A dimmers. (Wouldn't an overloaded wire also show damage more or less all along its length, rather than specifically at the end?)

    At any rate, it's somewhat of a moot question since it doesn't change what needs to be done to make things safe again: remove the toasted parts of the wires and the overheated terminal strips, and replace/reconnect using appropriate new hardware, and make sure everything is properly secured (which would also be very wise to double-check throughout the system).
     
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  8. EdSavoie

    EdSavoie Well-Known Member

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    Unless I'm mistaken, the connection at the end of the cable would always be the highest resistance, would it not? Regardless of what gauge wire is used, the connection is highly unlikely to be perfectly mating with every conducting surface of the wire.
     
  9. SteveB

    SteveB Well-Known Member

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    Not unusual for the wires in the strip that feed the actual branch circuits (pigtail of chassis mount) are #12, while the wires the install electricians ran from the dimmer rack are #8 or #10, to account for the length of the run.
     
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  10. RonHebbard

    RonHebbard Well-Known Member Premium Member

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    @EdSavoie Why do you feel the last connection in a series will be any poorer than the remainder??? Splain Lucy, splain.
    Toodleoo!
    Ron Hebbard
     
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  11. EdSavoie

    EdSavoie Well-Known Member

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    Because that's the part of the circuit with the greatest voltage drop in a given area?

    I think?

    EDIT: I think I understand what you were getting at, i meant in Isolation, not the complete series circuit.
    Relative to the conductor, the terminal connection is of higher resistance.
     
  12. RonHebbard

    RonHebbard Well-Known Member Premium Member

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    @EdSavoie Possibly you're going down a similar rabbit hole as one of my co-op students back in 1990. By Mark's logic; If a 1,000 Watt PAR64 consumed approximately 8 amps when operating at 120 volts then surely it must pull twice as much current when dimmed down to 60 volts. I suggested there was a flaw in his logic, if his theory was correct, there'd have been clauses in LD's contracts limiting the number and length of blackouts they were permitted to program in any one production. By extension, a 1,000 watt PAR 64 with zero volts applied would consume an infinite amount of amperage. Such was clearly not the case. (Not even up here north of Donald's walls.)
    Toodleoo!
    Ron Hebbard
     
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  13. IMLICHTMAN

    IMLICHTMAN Member

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    To amplify Mr. Terry's comment, though I don't recognize the specific nylon DIN-Rail mounted terminal blocks in the photos, nor can I reliably identify these as "mechanical clamping" or "setscrew" variants. I've seen countless terminations of multicore service cable flex-stranded conductors (think classic "borderlight" cable) under ill-sized flat or dog-point set screws where the strands basically walk around the set screw upon installation torque. In these instance there is simply not enough conductor cross section remaining to carry rated current. Assembly heating and subsequent thermal cycling will lead to similar failure of the terminal and adjacent wiring.
     
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  14. EdSavoie

    EdSavoie Well-Known Member

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    Exactly! If you're loading a circuit, the higher resistance of that terminal means that it dissipates more power than is lost in the cabling. In essence, it became a fuse.
     
  15. RonHebbard

    RonHebbard Well-Known Member Premium Member

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    @IMLICHTMAN A classic example of where crimp-on ferrules should be employed to contain all of the strands under the screw or, alternately, crimp-on pin terminals.
    Toodleoo!
    Ron Hebbard
     
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  16. STEVETERRY

    STEVETERRY Well-Known Member

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    Maybe, but "crimp-on ferrules" and "electrical contractor" rarely wind up in the same sentence.

    Ira's comments are spot on. Some types of terminals where the screw bears directly on the wire are OK for Class B 7-strand, Class C 19-strand, or solid conductors. However, 12AWG type SO multiconductor cables are generally 65 strands of 30AWG conductors--also known as Class K. This is to provide adequate flexibility, but this stranding CANNOT be terminated into a terminal where the screw bears directly on the wire. This misapplication will cause breakage and wind-up of the 30AWG strands. Terminals listed for Class K must have a clamping plate between the screw and the wire, or must use a tension clamp instead of a screw. Their conditions of listing will specifically mention Class K as an approved conductor stranding.

    I've got five bucks that says the terminals in the picture have the screws bearing directly on the wire.

    ST
     
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  17. RonHebbard

    RonHebbard Well-Known Member Premium Member

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    @STEVETERRY Are you speaking against crimp-on ferrules and / or crimp-on pin lugs or are you suggesting contractors wouldn't employ them??
    Toodleoo!
    Ron Hebbard
     
    Last edited: May 19, 2019
  18. STEVETERRY

    STEVETERRY Well-Known Member

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    The latter.

    ST
     
  19. JonCarter

    JonCarter Well-Known Member

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    When we ran into that fine stranding we'd get out the soldering iron, tin the last 1/2", stick it in the terminal & tighten it down.
     
  20. RonHebbard

    RonHebbard Well-Known Member Premium Member

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    @JonCarter Not recommended Jon, largely due to cold flow migrating away from the pressure of the bolt or screw. Ferrules are precisely sized by wire gauge, keep all the strands contained from escaping and protect the strands from damage; correctly sized and crimped Sta-kon / crimp-on pin terminals do likewise. I believe @STEVETERRY was in agreement with me but felt few contractors would source or employ correctly sized ferrules or Sta-kon pin terminals. Tinning stranded, and fine stranded, conductors is a fine idea prior to soldering in place but NOT when they're about to have a bolt screwed down on them leaving them free to migrate away from the point of applied pressure.
    Toodleoo!
    Ron Hebbard
     
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