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Thread: Why do they both trip???

  1. #11
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    Quote Originally Posted by George Stolz View Post
    I have done a continuity check on the load side of both breakers on all phases and there is none"
    I can't say that but I can say I can see the 480 feeder to the trans.

    It would be very very difficult for branch circuits to be mixed here. Buildings are separated by a 100'+ gap but there are bridge walkways with lighting so ...

    Weird stuff happens.
    You are right I cannot rule it out.

    Testing for it with transformers involved is going to be more than a basic continuity test at these breakers.

  2. #12
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    Did you wear your PPE when you moved that breaker to the different position?

  3. #13
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    Quote Originally Posted by peter d View Post
    Did you wear your PPE when you moved that breaker to the different position?


    You think I moved those breakers hot?

    The panel was dead.

    Did I wear PPE to verify it was dead? Nope.

  4. #14
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    "Sympathy tripping"...
    The 70 amp felt the 100 trip and joined in.
    At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.

  5. #15
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    What is the 30-45kva estimated transformer exactly feeding? Both the 70 and the 100amp conductors are separate or do they share conduit/raceways at any point?


    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.


    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)
    What is esoteric knowledge today will be common knowledge tomorrow.

  6. #16
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    Looks like magnetic trip adjustment is set to minimum setting on all three in question.

    Can't tell you where you should set them, but is possible you need to adjust them.

    Transient occasionally comes from supply and trips them at these low settings?

  7. #17
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    Quote Originally Posted by ptonsparky View Post
    Time for a camera setup again?
    That was my thought as well. One viable explanation is malicious mischief. But a camera pointed at the breakers could tell you something else: Do the two breakers actually trip at the same moment, or is there a delay between the trips?

    Another possibility is that the vibration imposed upon the panel when the first breaker trips is enough to cause the second breaker to trip. Moving the one breaker might cure this problem. Another troubleshooting technique would be to put the breaker back into its original location, but move the circuit conductors to another breaker. If the two breakers once again trip together, with the one being closed but having no wires attached, it would indicate that the breaker is showing its age, and needs to be replaced.

    Charles E. Beck, P.E., Seattle
    Comments based on 2014 NEC unless otherwise noted.

  8. #18
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    Quote Originally Posted by kwired View Post
    Looks like magnetic trip adjustment is set to minimum setting on all three in question.

    Can't tell you where you should set them, but is possible you need to adjust them.

    Transient occasionally comes from supply and trips them at these low settings?
    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.
    What is esoteric knowledge today will be common knowledge tomorrow.

  9. #19
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    Quote Originally Posted by charlie b View Post
    That was my thought as well. One viable explanation is malicious mischief. But a camera pointed at the breakers could tell you something else: Do the two breakers actually trip at the same moment, or is there a delay between the trips?

    Another possibility is that the vibration imposed upon the panel when the first breaker trips is enough to cause the second breaker to trip. Moving the one breaker might cure this problem. Another troubleshooting technique would be to put the breaker back into its original location, but move the circuit conductors to another breaker. If the two breakers once again trip together, with the one being closed but having no wires attached, it would indicate that the breaker is showing its age, and needs to be replaced.

    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)?
    What is esoteric knowledge today will be common knowledge tomorrow.

  10. #20
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    Quote Originally Posted by charlie b View Post
    That was my thought as well. One viable explanation is malicious mischief.
    Very limited access area, it would be lower management level mischief. Not out of the question but seems unlikely.

    But a camera pointed at the breakers could tell you something else: Do the two breakers actually trip at the same moment, or is there a delay between the trips?
    Very true.

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