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Thread: Mislabeled submersible pump?

  1. #1
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    Mislabeled submersible pump?

    I recently installed a VFD for a 20HP submersible pump used for irrigation.

    The customer added a backup 20HP pump last week, so we installed a double-throw switch ahead of the VFD to connect both.

    The new pump is causing an overload shutdown on the drive.

    Existing 20HP pump pulls 55A. The new pump pulls 66A. The box clearly says it’s a 20HP pump, and per the manufacture chart should pull 54.3A.

    Could the FLA vary that much, or is it likely mislabeled?

    Per the same chart the 25HP has an FLA of 65A. Just by the numbers I think they installed a 25HP.


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  2. #2
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    Quote Originally Posted by brantmacga View Post
    I recently installed a VFD for a 20HP submersible pump used for irrigation.

    The customer added a backup 20HP pump last week, so we installed a double-throw switch ahead of the VFD to connect both.

    The new pump is causing an overload shutdown on the drive.

    Existing 20HP pump pulls 55A. The new pump pulls 66A. The box clearly says it’s a 20HP pump, and per the manufacture chart should pull 54.3A.

    Could the FLA vary that much, or is it likely mislabeled?

    Per the same chart the 25HP has an FLA of 65A. Just by the numbers I think they installed a 25HP.


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    Just a thought are the motors physically the same size?
    Si hoc legere scis nimium eruditionis habes.

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    A double throw switch ahead of the VFD to connect both?
    Tom
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    Quote Originally Posted by ptonsparky View Post
    A double throw switch ahead of the VFD to connect both?
    I assumed either rather than both.
    Si hoc legere scis nimium eruditionis habes.

  5. #5
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    Do you have same flow rate, pressure and amount of lift for both pumps? Vary any of those and the motor shaft sees a different load. Difference in pump speed or impeller design can change flow or pressure when everything else is the same.

    ADD:

    In fact a restriction in one output line that goes unnoticed will lessen flow and will have lesser load on that pump with everything else being the same.
    I live for today, I'm just a day behind.

  6. #6
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    Submersibles often run into SFA. Is the pump running open discharge? Worst case scenario esp if it happens be a bit further down the hole.
    Tom
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    Quote Originally Posted by ptonsparky View Post
    Submersibles often run into SFA. Is the pump running open discharge? Worst case scenario esp if it happens be a bit further down the hole.
    It is ... they haven’t plumbed it into existing system yet. But so was the existing motor when I installed the Vfd.


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    If the pump has a bad bearing or anything else that slows it down, the amp draw will rise.

  9. #9
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    Quote Originally Posted by ptonsparky View Post
    ... if it happens be a bit further down the hole.
    The depth of the water, not the depth of the pump, determines the pressure difference across the pump.
    (along with other factors that are presumably constant)

  10. #10
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    Quote Originally Posted by drcampbell View Post
    The depth of the water, not the depth of the pump, determines the pressure difference across the pump.
    (along with other factors that are presumably constant)
    yes, I misspoke.
    Tom
    TBLO

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