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Thread: Multiconductor Cable Ampacity

  1. #41
    Join Date
    Aug 2004
    Location
    Northern illinois
    Posts
    16,476
    Quote Originally Posted by charlie b View Post
    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.

    575V motors are not real hard to get. my guess is that given the nature of the project it is likely they will get a spare motor anyway.
    Bob

  2. #42
    Join Date
    Dec 2008
    Posts
    497
    In my opinion, 3*#4 [compact stranded conductor,0.64 sq.in] is the maximum power cable
    allowed to pass through 1-1/4" RMC.
    If the conduit is embedded under 3 ft in concrete and 90 RHO soil 3*#4 copper conductor could withstand 103 A as per IEEE 835/1994 IEEE 835/1994- 0.6 to 5 kV Unshielded Single Conductor Extruded Dielectric Cable in Underground Duct Bank - Triplexed - Single Circuit
    25ºC Earth Ambient 90oC insulation rated table.
    Let's say the pump works 1 hr and 0.5 hr pause.Then Iav=sqrt(1*124^2/1.5)=101.25 A
    Another solution: a parallel cable of 3*#4 copper along the same path.
    It is not a beautiful solution but it could work for a while.

  3. #43
    Join Date
    Jul 2005
    Location
    Tennessee
    Posts
    15,853
    Quote Originally Posted by Julius Right View Post
    In my opinion, 3*#4 [compact stranded conductor,0.64 sq.in] is the maximum power cable
    allowed to pass through 1-1/4" RMC.
    If the conduit is embedded under 3 ft in concrete and 90 RHO soil 3*#4 copper conductor could withstand 103 A as per IEEE 835/1994 IEEE 835/1994- 0.6 to 5 kV Unshielded Single Conductor Extruded Dielectric Cable in Underground Duct Bank - Triplexed - Single Circuit
    25ºC Earth Ambient 90oC insulation rated table.
    Let's say the pump works 1 hr and 0.5 hr pause.Then Iav=sqrt(1*124^2/1.5)=101.25 A
    Another solution: a parallel cable of 3*#4 copper along the same path.
    It is not a beautiful solution but it could work for a while.
    Not only would it not be beautiful, it would not be legal (can't parallel less than 1/0)
    '
    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.

  4. #44
    Join Date
    Dec 2008
    Posts
    497
    I agree with you, augie47.A better solution, if there is a free path, to cancel the 3*#4 cable and run along the same path a suitable cable for ampacity and for voltage drop reason.

  5. #45
    Join Date
    Feb 2013
    Location
    India
    Posts
    2,404
    Quote Originally Posted by Julius Right View Post
    In my opinion, 3*#4 [compact stranded conductor,0.64 sq.in] is the maximum power cable
    allowed to pass through 1-1/4" RMC.
    If the conduit is embedded under 3 ft in concrete and 90 RHO soil 3*#4 copper conductor could withstand 103 A as per IEEE 835/1994 IEEE 835/1994- 0.6 to 5 kV Unshielded Single Conductor Extruded Dielectric Cable in Underground Duct Bank - Triplexed - Single Circuit
    25ºC Earth Ambient 90oC insulation rated table.
    Let's say the pump works 1 hr and 0.5 hr pause.Then Iav=sqrt(1*124^2/1.5)=101.25 A
    Thanks, JR. As for any unequal spacing in the triplex cable, any voltage unbalance at the 100 hp pump motor?

  6. #46
    Join Date
    Dec 2008
    Posts
    497
    As far as I know, triplex means that single-core cables are tied together so the center-to-center distance is the same. I think you intend to say separately laid single-core cables inegal distanced. The voltage drop depends on resistance and reactance -differences it could be if the phase length is different.The center line distance difference does not produce phase voltage drop difference.
    X=2.π.f(0.1404log10(S/r)+0.0153)x10^(-3) ohm/1000'
    Equivalent spacing S=(A*B*C)^(1/3) it is the common equivalent S for any of the phases.

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