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Thread: Tripping breaker

  1. #21
    Join Date
    Dec 2007
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    NE Nebraska
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    Quote Originally Posted by Ingenieur View Post
    I've designed more than a few sewage pump stations
    elec, mech and sanitary design
    in my experience they are typically over sized for peak demand and storm water infiltration

    I designed for a duty cycle of 25-30% avg
    10-20 low flow
    60-70 peak


    another consideration is retention time, in both the wet well and force main
    too long = septic
    you want to evacuate the fm every 4-6 hrs since no air in line
    it is a balance: too big = septic, too small friction loss, wasted hp

    the whole system needs reviewd
    piping
    well size
    pump size
    controls
    not only elec

    could be as simple as adjusting the level control
    Isn't duty cycle somewhat a guesstimate?

    When that new lift station goes in there are only 25 houses feeding into it. 50 years later that same station is still there, maybe a few parts have been replaced after wearing out but still mostly the same thing - but there is now 150 houses feeding into it. Thing happen over time.
    I live for today, I'm just a day behind.

  2. #22
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    Jan 2016
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    Quote Originally Posted by kwired View Post
    Isn't duty cycle somewhat a guesstimate?

    When that new lift station goes in there are only 25 houses feeding into it. 50 years later that same station is still there, maybe a few parts have been replaced after wearing out but still mostly the same thing - but there is now 150 houses feeding into it. Thing happen over time.
    isn't that obvious?
    it is all edtimates
    but you design for a service life of 10-20 years
    and current edu's x the areas population growth rate
    unless a new development, then for projected buildout
    and hope you can get the times you need with float adjustment
    some times vfd's are required
    sometimes 3 pumps
    it depends on the area

    have you done the capacity calcs for pump stations?
    we used water records

    one of the larger ones

  3. #23
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    Dec 2007
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    Quote Originally Posted by Ingenieur View Post
    isn't that obvious?
    it is all edtimates
    but you design for a service life of 10-20 years
    and current edu's x the areas population growth rate
    unless a new development, then for projected buildout
    and hope you can get the times you need with float adjustment
    some times vfd's are required
    it depends on the area

    have you done the capacity calcs for pump stations?
    we used water records
    My experience is service calls on mostly 40+ year old pumping stations in small villages.

    And there is almost always equipment that has been replaced or added that wasn't the original equipment either.
    I live for today, I'm just a day behind.

  4. #24
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    Quote Originally Posted by kwired View Post
    My experience is service calls on mostly 40+ year old pumping stations in small villages.

    And there is almost always equipment that has been replaced or added that wasn't the original equipment either.
    there are different scenarios
    extending sewers into new areas
    easiest because you know counts and new building rates
    although sewers will increase that some

    replacement of existing
    law requires hour meters, so flow can be estimated from pump down/in flow tests
    if you see 1 hr/day run time you know you have too much pump
    you can resize off of that data

    new development
    the toughest
    it may be sized for 50 homes but that may take 10 years
    so size for 25 and plan on upsizing in 5-10 years
    3 pumps: 1 for low flow, 2 for high, the 3rd is the required back-up
    vfd?

    I liked it
    it was challenging

  5. #25
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    Apr 2018
    Location
    Dubuque, Iowa
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    2
    It is not a new installation, and one of the 2 pumps is bad. The customer was concerned about the 60A breaker tripping ahead of the 50A. The response where one pump is running while the bad pump sits idle, and then try’s to start, that breaker is cold, but the 60A breaker has been protecting the other 50A breaker and pump. Seems to make sense. If there are any theories or ideas of why the 60A breaker would trip before the 50A breaker I would be glad to hear them.

  6. #26
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    Jun 2003
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    Quote Originally Posted by Djglennon62 View Post
    It is not a new installation, and one of the 2 pumps is bad. The customer was concerned about the 60A breaker tripping ahead of the 50A. The response where one pump is running while the bad pump sits idle, and then try’s to start, that breaker is cold, but the 60A breaker has been protecting the other 50A breaker and pump. Seems to make sense. If there are any theories or ideas of why the 60A breaker would trip before the 50A breaker I would be glad to hear them.
    See post 5 again. Then look at post 2. We don’t know how bad your motor is but it is not that unusual for a 100 or even a 200 to clear before the 50 does on a fault. It is not what we want to happen but it does or I should say, it can.
    Tom
    TBLO

  7. #27
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    Dec 2012
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    Placerville, CA, USA
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    Quote Originally Posted by ptonsparky View Post
    See post 5 again. Then look at post 2. We don’t know how bad your motor is but it is not that unusual for a 100 or even a 200 to clear before the 50 does on a fault. It is not what we want to happen but it does or I should say, it can.
    And one reason that it can is that the time-current trip curves of two different size breakers, even in the same line from the same manufacturer, may be shaped such that the trip current versus time curves of one breaker cross those of the other, leaving a region of time and current combinations that trip the nominally larger breaker first.
    This is less likely to happen with "identical" fuses of different nominal ratings, but is still possible.

  8. #28
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    Dec 2007
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    The higher the available fault current the easier it may be for this to happen also.

    Since you have 50 and 60 amp breakers involved their instant trip settings are likely fairly close to one another. In the 60 is probably supposed to be higher, especially if both are same series of units, but time and deterioration can have impact plus any tolerances that were allowed in the manufacturing.
    I live for today, I'm just a day behind.

  9. #29
    Join Date
    Nov 2014
    Location
    Miami, Florida, USA
    Posts
    120
    Strikes me as strange to have a 60 amp main with two 50 amp pump breakers. That isn’t what I’m used to seeing.

    Might be worth the time to find out who made pump panel and makes sure 60 was the intended size. People will use what they have in an emergency.

    And for pete’s sake, if you have known bad pump remove it from service and get it replaced ASAP.

    FWIW, had good service from Flyght pumps and Stacon panels. Heck if nothing else contact them with pump specs, ask for a quote, and see what they size breakers at.

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