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Thread: Things that make you go Hmmmmm.

  1. #1
    Join Date
    Sep 2017
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    Phoenix AZ
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    Things that make you go Hmmmmm.

    Greetings, I came across something interesting here, hopefully one of you folks can explain....at a restaurant, 3- 200A 3 phase 120/240 42 space panels. Voltage readings were 120v to ground and neutral on A and C phase, B phase seems to have a high leg, of course, phase to phase readings were common 240V, I realized there were many single pole breakers on B phase !!!!! I performed readings at breaker(s) output to ground and neutral and all were 120V !!, then I took readings again at line and load side of MCB , on B phase, ...180V ....bussing in panel was at 120V........I am not understanding this !!!! , what am I missing here?, any input would be hopeful and helpful....THX....Dean

  2. #2
    Join Date
    Feb 2009
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    Durango, CO, 10 h 20 min without traffic from winged horses.
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    What brand is the panel? I remember working on an old SQD that was bussed B,C,A. The high leg was still on B, but it was in a different breaker position than one was used to seeing.

    Also some old high leg systems have high leg on C.
    Once in a while you get shown the light
    In the strangest of places if you look at it right. Robert Hunter

  3. #3
    Join Date
    May 2014
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    AZ
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    waiting in a line to buy a $2 item and you expect that line to go rather fast, but for some reason it takes 30min to get through checkout, makes me go " hmmmmm, hmmmmmmm, hmmmmmm ", a few times while waiting

  4. #4
    Join Date
    Dec 2006
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    Chapel Hill, NC
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    So you are saying that there was a voltage difference when measuring before the breaker and after the breaker? This doesn't seem possible unless there is some special breaker that can regulate the high leg.

    It certainly seems like you have a delta 3 phase but I have no idea how the voltage after a breaker changes
    They say I shot a man named Gray and took his wife to Italy
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  5. #5
    Join Date
    Jun 2003
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    NE (9.1 miles @5.07 Degrees from Winged Horses)
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    Take a voltage reading line to bussbar on each phase. Some one may have modified the panel.

    Makes sure of your readings.
    Tom
    TBLO

  6. #6
    Join Date
    Apr 2009
    Location
    Williamsburg, VA
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    4,172
    Welcome. Either it has a high leg or it doesn't.... "B phase seems to have a high leg" does not compute. It would be possible to use the high leg to run single phase 208V loads with a neutral, hence your apparently seeing 1p breakers on it. This is rarely done and when it is, it's usually done wrong. That you have 180V instead of 208V seems to suggest there is a pretty massive voltage drop on the high leg.

    Breakers cannot magically transform bus voltage into a different line voltage.
    Electricians do it until it Hertz!

  7. #7
    Join Date
    Jul 2006
    Location
    San Francisco, CA, USA
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    6,771
    Bad connections with your meter probes?
    __________________________________________________ ____________________________
    Many people are shocked when they discover I am not a good electrician...

  8. #8
    Join Date
    Dec 2007
    Location
    NE Nebraska
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    32,914
    Can you please clarify what two points you were measuring 180 volts between?

    You possibly describing a bad "B" pole on the breaker and the 120 to ground you are seeing is "back feed" voltage through loads connected to A or C phase as well as to B phase? 180 is maybe what you read from line to load terminal of the B pole of the breaker?

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