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Thread: Why do they both trip???

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  1. #1
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    Why do they both trip???

    Here is the deal, for long time we have had a customer that has some breakers that have been tripping.

    Here is the panel I am dealing with, it has a 200 amp main breaker at the top and down at the bottom you can see two - 3 pole breakers, a 70 and a 100.

    The other night I went there and the 200 amp main, 100 amp feeder and 70 amp feeder were all in the tripped position.




    Below is the main breaker.


    Here are the two 3-pole breakers




    The 200 amp breaker supplies the panel from an ATS right beside it. In turn the ATS is supplied from switch-gear very close by. I would say the supply is very stiff, over done in house engineering. (Not a complaint, just saying they use a lot more copper than is likely required)

    The 100 amp breaker supplies a panel 400'-500' away in a separate structure. This is an underground run, around 500 Kcmil copper in PVC. The load in less than 20 amps on all three legs. The panel supplies LED egress and exit lighting, a fire alarm booster panel and other small loads.

    The 70 amp breaker is the primary supplying a transformer directly above the panel, lets say 15' to 20' of conductor from breaker to transformer. I did not check but suspect the transformer is a 30-45 kVA unit. 480-208Y/120.


    We all suspect the underground run is failing, each time there has been a trip over the course of maybe two years and five or six trips the ground has been wet or moist.

    I did use a basic mega meter on it and it went to the end of the meters scale.

    Monday night I am meeting a testing company on site to do some type of advanced testing on the conductors.

    Now here is the real question I have.

    Regardless of the fault being on the 100 amp breaker or the 70 amp breaker why are they both tripping?

    I understand the main and one feeder going to the tripped position at the same time but why are two unrelated feeder breakers tripping at the same time?

    This has happened each time, always both breakers tripped.

    Grasping at straws while there the other night I decided to move one breaker away from the other on the thought one was somehow tripping the other?? Magnetic field?? Just the sharp rap of one breaker tripping causing the other to go??? I have no clue but I did move the breaker.

    Anyone have some insight? A technical reason for this? Poltergeists?

    Last edited by iwire; 03-13-17 at 06:14 AM.

  2. #2
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    My first thought was you need a coordinated study and an adjustment needs to be made on the main. It seems that there can be a large load on the same area so that the breakers are heating up. My other guess is possible poltergist

  3. #3
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    Quote Originally Posted by Dennis Alwon View Post
    My first thought was you need a coordinated study and an adjustment needs to be made on the main. It seems that there can be a large load on the same area so that the breakers are heating up.
    All three breakers have negligible loads on them. They supply only required emergency circuits. You can run a lot of LED fixtures exit signs at 277 volts without seeing much draw.


    My other guess is possible poltergist


    Its as good as anything I can come up with. I am really at a loss to explain why both breakers trip.

  4. #4
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    If the 3p breaker on the bottom controls lighting then I am guessing that a ballast is heating up and somehow shorting to ground. The main can trip if it is weak or it is not set correctly. Isn't that an adjustment I see or does that changes the actual amperage of the breaker.

  5. #5
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    Quote Originally Posted by Dennis Alwon View Post
    If the 3p breaker on the bottom controls lighting then I am guessing that a ballast is heating up and somehow shorting to ground. The main can trip if it is weak or it is not set correctly. Isn't that an adjustment I see or does that changes the actual amperage of the breaker.
    The issue I am having is why do both the 100 and 70 amp feeder breakers always trip at the same time*. They supply separate loads.

    It is as odd as having two branch circuits trip at the same time repeatedly and only one of the circuits seems to have an intermittent fault.


    (* To be clear, all I know for sure is both breakers are tripped when we arrive which is 30-120 minutes after the call came into us.)

  6. #6
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    Grasping at straws, but I would check to see that the 70A and the 100A are entirely electrically isolated on their load side. If they are not, a short circuit or ground fault on either would trip the other. The 200A being dialed to minimum would indicate that the 200A and the others would tend to be pretty close in a short circuit or ground fault horse race. I would google the scale for the 200A min/max settings and see what the dial does for certain, and turn it up an informed amount to get it to slow down a bit for the supplied breakers to finish sooner.

    Edit: it could very well be that for a 200A trip plug, the max setting on that breaker is required for an actual 200A - I'd have to google the breaker spec sheets to know what it's controlling for sure.

  7. #7
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    Quote Originally Posted by George Stolz View Post
    Grasping at straws, but I would check to see that the 70A and the 100A are entirely electrically isolated on their load side. If they are not, a short circuit or ground fault on either would trip the other. The 200A being dialed to minimum would indicate that the 200A and the others would tend to be pretty close in a short circuit or ground fault horse race. I would google the scale for the 200A min/max settings and see what the dial does for certain, and turn it up an informed amount to get it to slow down a bit for the supplied breakers to finish sooner.

    Edit: it could very well be that for a 200A trip plug, the max setting on that breaker is required for an actual 200A - I'd have to google the breaker spec sheets to know what it's controlling for sure.
    I wondered if they could have phases crossed to the wrong breakers but the wires appear to be different sizes. That and Iwire moved the breakers around so that theory was thrown out the window.
    Tom
    TBLO

  8. #8
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    Quote Originally Posted by George Stolz View Post
    Grasping at straws, but I would check to see that the 70A and the 100A are entirely electrically isolated on their load side.
    For sure it could happen seen it a couple times with branch circuits.

    In this case I can see the entire run from the 70 up the side of the panel and into a conduit up to the transformer.

    OTH, The 100 amp feeder is a bit funky, the conduit to the other structure comes up under the floor mounted ATS that was a mistake so they ran a conduit out the top of the panel, over and down into the ATS using the bottom of the ATS to splice the say 1 AWGs on the breaker to the larger conductors running to the other structure.

  9. #9
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    Once I had a maintenance electrician call me out to the plant to look at a panel that had multiple breakers that had tripped simultaneously. He couldn't figure out why and neither could I. We later learned that a tow motor hit the beam that the panel was mounted on at the time of trip. That's when I learned that QO breakers can go to the tripped position on a mechanical shock event.


    Sent from my iPad using Tapatalk

  10. #10
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    Quote Originally Posted by retirede View Post
    Once I had a maintenance electrician call me out to the plant to look at a panel that had multiple breakers that had tripped simultaneously. He couldn't figure out why and neither could I. We later learned that a tow motor hit the beam that the panel was mounted on at the time of trip. That's when I learned that QO breakers can go to the tripped position on a mechanical shock event.


    Sent from my iPad using Tapatalk
    Nearly all modern modeled case circuit breakers will trip on a large enough shock event. The magnetic trip function is simply a movable strip of metal, so anything that send it jolting will trip the breaker.
    What is esoteric knowledge today will be common knowledge tomorrow.

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