9 Conductors

I am getting ready to install a 500Hp 480volt three phase motor on a piece of equipment powered by a VFD. I will be running 9 conductors to the motor not including grounds. These conductors will be running in 3 - 3/1/2 ridged conduits. What is the best practice to run 3 conductors in each conduit and separate them by phase, Phase 1 in a conduit Phase 2 in a conduit and Phase 3 in a conduit or have conduit 1 running an U1,V1 and W1 conduit 2 running U2, V2 and W2 and conduit 3 running U3,V3 and W3 and then pairing up the U's, U1, U2, and U3. the V's V!, V2, and V3 and the W's W1, W2, and W3 at the motor. Is there Harmonics or EMF generated that should be taken into consideration. The wire is "Tray Rated" 500MCM THHN

by ddt01
5 days, 19 hours ago
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2 Answers

Answer by Foxx

Just to make sure I understand, you plan on running 3 conductors in parallel for each phase and you have 3 conduit runs. Is this so? If it is, each conduit should carry one conductor from each phase and I would be surprised if whatever code you are working under does not require this. If you put three parallel conductors of one phase in an iron conduit you get a magnetic field induced in the iron which heats the iron quite possibly to a dangerous level and also puts an extra impedance in series with the motor feed. If you are using plastic conduit, situation is not as bad but it is still poor practice

+1 vote
by Foxx
5 days, 12 hours ago
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Answer by ddt01

Thank You Foxx. That's why I was asking

+1 vote
by ddt01
4 days, 19 hours ago
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