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Thread: Multiconductor Cable Ampacity

  1. #31
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    Interesting concept, Gus. I'll look into it. This specific application cannot work with a VFD. But raising the voltage at one end and reducing it at the other end is worth a review.
    Charles E. Beck, P.E., Seattle
    Comments based on 2017 NEC unless otherwise noted.

  2. #32
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    Quote Originally Posted by charlie b View Post
    Interesting concept, Gus. I'll look into it. This specific application cannot work with a VFD. But raising the voltage at one end and reducing it at the other end is worth a review.
    You would end up with roughly 150 amps of 480 available based on 125 amp rating of #4 (not considering transformer losses)
    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.

  3. #33
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    Quote Originally Posted by charlie b View Post
    Interesting concept, Gus. I'll look into it. This specific application cannot work with a VFD. But raising the voltage at one end and reducing it at the other end is worth a review.
    Can you step up your voltage to 600V, and use a 600V (575V) motor at the pump, to save the cost of a second transformer?


    SceneryDriver

  4. #34
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    Quote Originally Posted by SceneryDriver View Post
    Can you step up your voltage to 600V, and use a 600V (575V) motor at the pump, to save the cost of a second transformer?


    SceneryDriver
    I suggested something along those lines earlier but he did not respond so I guessed the thing was already bought.
    Bob

  5. #35
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    Nothing has been purchased yet, and all ideas are on the table. Reliability is a very important aspect. Adding two transformers brings two possible failure points into the equation. Adding one transformer only brings one failure point. So it is worth considering.
    Charles E. Beck, P.E., Seattle
    Comments based on 2017 NEC unless otherwise noted.

  6. #36
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    100 hp is in the range of needing around 112.5 kVA transformer. Actually a pair of them or one transformer and one 575 volt motor - which unless you are in Canada is likely higher cost and maybe even longer lead time to get it. If you smoke that motor for whatever reason and don't have a spare - possibly longer down time to get a 575 volt replacement then a 460 volt replacement. Special frame size or other spec feature - maybe don't matter, maybe even stuck with an OEM being the most easy to obtain and don't get to choose other voltage or other characteristics. NEMA standard motor - just about any 460 volt motor with same speed and enclosure type suitable for the application would work and is likey not too difficult to come up with on short notice.

    I'd probably still look harder at how to install larger raceway/conductors even if it has to take a different route then what is existing. Go even higher then 600 volts and necessary conductor gets even smaller, but insulation gets thicker.
    I live for today, I'm just a day behind.

  7. #37
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    Quote Originally Posted by kwired View Post
    100 hp is in the range of needing around 112.5 kVA transformer. Actually a pair of them or one transformer and one 575 volt motor - which unless you are in Canada is likely higher cost and maybe even longer lead time to get it. If you smoke that motor for whatever reason and don't have a spare - possibly longer down time to get a 575 volt replacement then a 460 volt replacement. Special frame size or other spec feature - maybe don't matter, maybe even stuck with an OEM being the most easy to obtain and don't get to choose other voltage or other characteristics. NEMA standard motor - just about any 460 volt motor with same speed and enclosure type suitable for the application would work and is likey not too difficult to come up with on short notice.

    I'd probably still look harder at how to install larger raceway/conductors even if it has to take a different route then what is existing. Go even higher then 600 volts and necessary conductor gets even smaller, but insulation gets thicker.
    I think it is a pump down inside a well so would not be a standard motor anyway.
    Bob

  8. #38
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    Something else you may consider is using a smaller sump pump that runs continuously or nearly so. No problem then with raceway fill, voltage drop, etc.

    I would double check to make sure there is not room for 90*C terminations on each end before writing it off.

    as for the pump not running continuously, I would think a mechanical interlock or timer to prevent that is the only acceptable solution. Just because a worst case scenario would not require the pump to run for 3 hours, you have to consider failure of float switches, maintenance on other pumps that takes them offline, somebody leaving the H - 0 - A switch in hand or manual operation, etc.

    If variable speed is not possible, throttling discharge valves would run the pumps longer, however it would reduce the number of start cycles per hour
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  9. #39
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    Quote Originally Posted by petersonra View Post
    I think it is a pump down inside a well so would not be a standard motor anyway.
    Making it an OEM type of motor and may be even more difficult to find in 575 volts - if same manufacturer sells to Canada - maybe a better chance.
    I live for today, I'm just a day behind.

  10. #40
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    Quote Originally Posted by petersonra View Post
    I think it is a pump down inside a well so would not be a standard motor anyway.
    The "well" is about 8' x 8' x 18'. The pump is in the sump, but the motor is 45' above the pump, and a very long shaft connects them.

    Charles E. Beck, P.E., Seattle
    Comments based on 2017 NEC unless otherwise noted.

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