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shunt breakers

Discussion in 'Question of the Day' started by ship, Feb 18, 2007.

  1. ship

    ship Senior Team Emeritus Premium Member

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    So way back when - like 15 years ago, I had as the position of second TD in the history of this actor generated "I have a barn, let's do a show" theater company, who had this second floor theater in a building whichstarted off in the 1920's as a doctor's office, and last I knew was some form of church. No idea of what it is now - seriously no idea and expect it's been seriously modified much less re-wired. We had the entire top floor for our two theater's and various offices and shop spaces, the lower part had five store front stores. Our theater company went out of business for all intensive purposes about in 1996... Had a good run as a theater, we all got older and couldn't sustain it amongst lots of reasons to put the place and dream to bed.




    I at the time found curious the Main-Breaker/Sub Panel arrangement that was confusing and permitted by code. Power for all buildings came in to the lower floor corner of building hot dog stand which had all the building's meters and main breakers. Could reach out my office window and touch the feeder cable that fed the place from the pole. From there, each occupancy had it's own indivudual main panel. Nothing big there about a main breaker at the meters and a second one in an individual unit, this except in my theater I found.

    We had a main panel, three sub-panels, two switch panels and one un-breakered panel that was in another room yet somehow controlled not persay directly by the main panel, yet you shut off the main, it would go off. None of the wiring for this speific panel, or the various sub or switch panels it fed had wiring that directly linked it to the main panel in our part of the building. Nor was there a main breaker for this sub-panel of sorts.

    Main single phase three wire 100A panel was breakered for it's various uses including the non-battery supplemented exit lights, two sub-panels - one remote one in the same electrical closet, with a non-used front of building lighting timer switch. (All for the most part with some various upgraded sto the normally origional 1920's cloth covered wiring in the origional part of the space.)

    Than there was the "other" main panel which controlled another newer sub-panel and the 100A single phase three wire fuse sub panel which was used for the dimmers. All of this was in theory installed during the re-construction of the office space into a theater complex.

    The "other" panel without any main breaker somehow was tied into the main circuit breaker panel origional/replacement to the building that was located below the bank of power company meters for the complex, in the hotdog stand. This under a similar 100A three wire single phase power supply, yet somehow in addition to ability to turn it off down stairs, you could turn it off by way of the older origional install / replacement at some point in type main panel's circuit breaker which was just a normal two phase Square D type QOU (if memory serves in being very normal) for it's main circuit breaker to the building which seemingly somehow controlled all electric on the floor.

    Beyond this "shunt breaker" concept, at some point, we grew and got more dimmers. Right about the time I took over as TD - fresh out of college or still in, we melted down our "Main" circuit breaker for the fused dimmer switch powereing up from the un-breakered sub-panel that fed the dimmers. Smelled like burnt plastic all over the storage/dressing room. Hmm, smelled this smell before, breakers didn't trip so I was I suppose too young to worry much given saftey equipment in place. Was in my office one night as the stage manager came in staying that they were only getting about half their lights up and running at random and of course it was the first act of "opening night." I had designed the show but neglected to fully understand the concept of "balanced load" - this especially on a single phase three wire system.

    Thought I had balanced my load, but perhaps in some way I didn't really balance it sufficiently in doing a scene for scene look at it as opposed to in general 20A = 20A type of one. This scene for scene perhaps by way of bad luck in an un-usual loading that just happened to be upon a single phase of two phases. Say blues mainly wound up on one phase, ambers on another phase. Thus say a night scene would be bad luck in balanced load.


    Did the best I could with what I could pull up so as to cover the stage and write cues on the fly and investigated. This breaker had melted down and was missing a phase of power - luckily at least the dimmer fans were on a different phase, or by way of premium 1979 technology, if the fans on the dimmer packs were on the same phase as that which stopped working, the dimmers also didn't overcook without fans. 100A two phase breaker at the un-master breaker sub-panel/main panel had definately melted down without tripping, one leg was still working to some extent, the other melted away at some point during the opening scene.

    Breaker on this feeding the dimmer switch never tripped. Fuses on the dimmers it fed and down line from it in in-theory blowing first never blew either. For some reason also (perhaps fortunate given our exit lights were in the same system, and there was no battery backup,) neither the "main breaker" in the electrical closet tripped, nor did the one in the hot-dog stand all were tied into. Conductors and actual circuit breakers stared melting without tripping any overload protection in any way. Beyond "tripping our main", had the one in the hot dog stand tripped as in theory it should have, we didn't have keys to the place and will have been shut out for the night. Yet if some form of shunt breaker that also shut off our shall we say "shunt" sub-main panel, why didn't it trip it's main in saving the wiring feeding that panel and offering some form of protection?

    Instead, during intermission in a "show must go on" type of way, I did a while still hot replacement of the main breaker for the dimmers - couldn't shut off the main as it were shunt breaker for the building, best I could do was pull the fuse/switch load at the dimmer end and tape as best I could it's melted wires before installing a new just happen to have extra breaker into some un-melted down slots on the panel. Than did a quick re-distribution of power and played cues by ear for the rest of the night.

    Yep... total hack and not at all what I would do today in any way of description, this much less in part my concerns about others becoming "ME" or "TD" for shows/theaters in a = gee this is what I experienced in risking the lives of my audience while new, what can others's attempt to do their job as best they can do to also risk the lives of their audience type of way?

    So, question of the day:

    How did that main-panel which was un-breakered work as some form of shunt breaker system with the main panel on our floor?

    After that, why did the circuit breaker feeding the fused switch dimmer supply literally melt down without tripping or blowing a fuse all of which were up-line of the mounting lugs for the breaker that melted down?

    Next, why didn't either the shunt breaker or the per-say main breaker in the hot dog stand trip long before a circuit breaker melted down?

    Beyond that, in stuff like premium 1979 technology TTI 6-pack dimmers perhaps not needing a fan for a short duration of time as explination on why they didn't also melt down given this appairently seriously un-balanced load. How one can so seriously overload four packs of 2.4Kw 6-channel dimmer packs that they could melt down a two phase 100A circuit breaker if not the switch in line for them first.. This amongst other stuff.
     
    Last edited: Feb 19, 2007

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