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#218803 10/17/17 08:50 AM
Joined: Mar 2003
Posts: 849
two 15 HP 480 pumps VFD's Located in building 800 feed away. ( Pumps in a flood plane area) .
Is there a Problem running two feeders from VFD;s in same conduit the 800 Ft .
The reason I ask is I heard there could be a interference problem between cables in the same
raceway. They know they might lose the pumps but want to keep the VFD's out of harms way.

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Joined: Jul 2004
Posts: 9,677
Likes: 9
If the feeders were twisted it should eliminate the cross talk but I am not sure how you do that unless you pull a cable that is twisted (like SER)
At the frequencies we are talking about you don't really need that much twist. You might be able to get a twist in each set as you are feeding them in.
Are you doing this all in one pull?

Greg Fretwell
Joined: May 2005
Posts: 984
Likes: 1
I wouldn't only be worried about crosstalk; I'd be concerned about the 800 foot distance between the VFD and the motor unless appropriate filters are installed.

Joined: Jul 2004
Posts: 9,677
Likes: 9
Voltage drop will be tough too. figuring FLA at around 20a, you need #6 cu to keep the drop around 3%

Greg Fretwell
Joined: Mar 2003
Posts: 849
1 conductors per phase utilizing a #4 Copper conductor will limit the voltage drop to 2.49% or less when supplying 30.0 amps for 800 feet on a 480 volt system.
For Engineering Information Only:
70.0 Amps Rated ampacity of selected conductor
0.2957 Ohms Resistance (Ohms per 1000 feet)
0.048 Ohms Reactance (Ohms per 1000 feet)
14.399999999999999 volts maximum allowable voltage drop at 3%
11.933. Actual voltage drop loss at 2.49% for the circuit
0.9 Power Factor

21 amps x 125% =26.25 round up to 30 amps for safety .

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