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Unbalanced power distribution on 208v units only.

Discussion in 'Lighting and Electrics' started by McCready00, Aug 10, 2018.

  1. McCready00

    McCready00 Active Member

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    Hello all,

    Could someone tell me which problems could an unbalanced power distribution produce.

    I understand, and can also calculate, what will return to neutral, and why it could be a big problem when working on fixtures, dimmers or whatever else using 120v.

    Although, if only using fixtures on 208v, where neutral would still be low enough, and phases are really unbalanced... what could be the problems ?

    That question also applies when power is supplied/or not from a generetor.

    Thank you
     
  2. JD

    JD Well-Known Member

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    Although in an ideal world, all phases would balance equally. In the real world it rarely happens. If your source is Wye (120,120,120 with 208 between), then running only 208 loads means you are loading Delta. Not a problem. Any one fixture will load two of the three legs. As long as your source (company switch or generator) can handle the highest current found on any one leg, then you are fine. So, if your source was 100 amps per leg, and your load was 100, 100, 0 you would still be fine. Because you are limited to the current on the highest leg, your ability to use all the power available to you is decreased.
     
    RonHebbard likes this.
  3. TJCornish

    TJCornish Well-Known Member

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    208v fixtures do not contribute to neutral current or triplen harmonics. This is indeed a good way to go. Balance phase loading as best you can and you’ll be fine.
     
    RonHebbard and JD like this.
  4. DavidJones

    DavidJones Active Member

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    Having phases out of balance can be a lot more of an issue on a portable generator. Having unbalanced loads will cause the generator to become physically unbalanced and can actually damage the unit. New generators will shut themselves down before this happens, but you are still going to lose power.
    It's typically very easy to load balance fixtures with portable power since soca outputs are usually wired

    1: x-y
    2:y-z
    3:z-x
    4: x-y
    5:y-z
    6:z-x

    Provided you are using the same fixture types or rotating your circuiting so the close to the same number of each fixture types land on each leg, It usually comes out really close.
     
    RonHebbard likes this.
  5. McCready00

    McCready00 Active Member

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    How to balance and how distros are wired, that informations I already know pretty well.

    JD + TJCornish, thanks for your answer altough I was more looking for that following information;

    DavidJones
    That is exactly the information I need to understand.. You've got more details on what you just wrote? I knew it could be bad on a generator...
     
  6. DavidJones

    DavidJones Active Member

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    Sorry for the delay. You have to consider the strength of the engine turning the generator, compared to the load you are placing on it. The reality is that as long as you are not nearing the capacity of a generator, you can be pretty unbalanced and it won't be a problem. Power factor is a much bigger problem, but that is a whole other ball of wax. Most of the modern genies will just flip the main off if there is a problem, older ones that don't have the advanced controllers might just kill the engine if it's very unbalanced. Unbalanced load and bad power factor on shore power is not really an issue because the grid is robust enough to absorb all of those problems. An unbalanced load is like a 3 person bicycle, if one person jams on the brakes, it can bring the whole bike to a halt.

    The main reason for load balancing is not really to protect the generator but to make sure you are utilizing your power efficiently and not tripping the breaker before because of just one leg. On a rock show If your whole rig should draw 90 amps per leg at full tilt, its probably fine to use a 100 amp service, because it won't be on at full all the time, and even if at the end of a song, an LD cranks up all the blinders and strobes at once, its still for a very short duration. Now If you inadvertently put all the Blinders on one leg, because sensor dimmers are wired in blocks of 8, then you could be running one leg drastically higher than the other two, and trip the main breaker, even though if it were evenly spread across phases, there would not be a problem.
     
  7. DavidJones

    DavidJones Active Member

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    Richard Cadena is the leading authority an all of these things. He teaches classes. I highly recommend it.
     

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