1. Senior Member
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Aug 2004
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Northern illinois
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Originally Posted by charlie b
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.

2. Senior Member
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Dec 2008
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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. Originally Posted by Julius Right
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)
'

4. Senior Member
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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. Senior Member
Join Date
Feb 2013
Location
India
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2,404
Originally Posted by Julius Right
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. Senior Member
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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