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Thread: Why do they both trip???

  1. #21
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    Quote Originally Posted by mbrooke View Post
    Ok, here is where my limited knowledge will shine, but I can't help but notice something in the pics. The 277 volt GE breakers I am familiar with all trip to the center, but in this pic they (the handles) appear to be in the off position. My question is did someone move them after to the "off" position or do these trip to the off position when called to operate automatically (short circuit)?
    They look like they are in the on position to me.
    Cheers and Stay Safe,

    Marky the Sparky

  2. #22
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    My guess is that you need to turn the magnetic settings up on all 3 breakers. A coordination study would tell you how much.

    Is there also a transformer on the 70 amp feeder?

    Maybe when they test the generator, and when the transfer happens, if the timing is just right there is enough inrush on both feeders to cause both breakers to trip, and one also has enough to trip the main.

    Kudos to you for not turning everything to "max" as soon as one breaker tripped. I think that's the normal troubleshooting method.

  3. #23
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    Quote Originally Posted by mbrooke View Post
    What is the 30-45kva estimated transformer exactly feeding?
    A 208Y/120 panel for required emerngency circuits only.


    Both the 70 and the 100amp conductors are separate or do they share conduit/raceways at any point?
    Other than the panel separate,


    I am with George on this. Its possible the 70 amp and 100amp are crossed somewhere which is enough to show up on a ground fault.
    See my response to George.


    As for the 200 and 100amp tripping (as already mentioned) uncoordinated breakers will fight each other when the fault current exceeds the instantaneous trip rating. This is especially true if the source impedance is low (ie plenty of available short circuit current as is common with high amp 480 volt services)
    This is not what I am asking about.

    I understand why breakers in series with each other can both trip it is actually pretty common.

  4. #24
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    Quote Originally Posted by K8MHZ View Post
    They look like they are in the on position to me.
    Just looked at the pics again. They are. My eyes latched onto number 22 and 34
    What is esoteric knowledge today will be common knowledge tomorrow.

  5. #25
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    I took a quick look at the bulletin for these breakers and it look like you may want to move the adjustment off of "min" for the 200 and the 70 for the transformer feed per their suggestion. That doesn't explain the 100 amp going, however.

  6. #26
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    Quote Originally Posted by iwire View Post
    A 208Y/120 panel for required emerngency circuits only.
    Just lighting or any motor/inrush loads on it as well? Typical Delta wye transformer, right?
    What is esoteric knowledge today will be common knowledge tomorrow.

  7. #27
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    Quote Originally Posted by mbrooke View Post
    Believe it or not breakers are rarely (if ever) adjusted past the factory settings in most installations when installed.

    However I agree those need to be raised, but not to knock on anyone its best left up to an engineer experienced in short circuit studies and selective coordination.
    Which is why I mentioned I don't know where they should be set, but as is they possibly are at a lower magnetic trip setting then all the breakers that don't have an adjustable magnetic trip, which is very well why those three are the only ones that are tripping.

  8. #28
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    Quote Originally Posted by steve66 View Post
    My guess is that you need to turn the magnetic settings up on all 3 breakers. A coordination study would tell you how much.
    Respectfully I see no connection between the mag settings and two breakers protecting different circuits tripping at the same time.

    If there is a fault on the 100 amp breaker how is that tripping the 70 amp breaker located across from it?



    Is there also a transformer on the 70 amp feeder?
    Yes.

    Maybe when they test the generator, and when the transfer happens, if the timing is just right there is enough inrush on both feeders to cause both breakers to trip, and one also has enough to trip the main.

    Hmm, this exact issue has happened in the past and I was able to fix it by programing in a transition delay into the transfer switch.

    Instead of transferring directly back to utility from the live generator it paused for a time in between. It seemed to have worked for me twice in the past.

    Sitting here at my desk I doubt they run the genset in the middle of the night for testing but I really do not know. I will tell you this I am going to check on the exerciser schedule and if they exercise with load. I am going back tonight to assist the testing company.



    Kudos to you for not turning everything to "max" as soon as one breaker tripped. I think that's the normal troubleshooting method.
    It is just not a decision I make and it comes up pretty often.

  9. #29
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    Quote Originally Posted by kwired View Post
    Which is why I mentioned I don't know where they should be set, but as is they possibly are at a lower magnetic trip setting then all the breakers that don't have an adjustable magnetic trip, which is very well why those three are the only ones that are tripping.
    I understand and I fully agree.
    What is esoteric knowledge today will be common knowledge tomorrow.

  10. #30
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    Quote Originally Posted by gadfly56 View Post
    I took a quick look at the bulletin for these breakers and it look like you may want to move the adjustment off of "min" for the 200 and the 70 for the transformer feed per their suggestion. That doesn't explain the 100 amp going, however.
    Hey thanks.

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