1 load in multiple conduits

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pault587

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Grand Rapids, MI
I have an application for a control panel that has a load of 480V 3 phase 436 amps. I am planning on using a 600 amp breaker to feed this panel. My question is if I want to use 350 kcmil 2 per phase do I use 3 conduits one for each phase or 2 conduits each phase in one conduit? The control panel spec says it can receive (2) 3in or (3) 2-1/2in conduit.

I was told yesterday that you must have each phase in a run. My electrician says that will be harder to run and wire.

Thanks in advance,
Paul
 
Being an electronic equipment engineer, you are aware that with AC circuits the magnetic fields cancel when in close proximity. You are allowed to run conductors in parallel with each phase in a single conduit, some times this is easier, but more often its one conductor from each phase in a conduit. Conductor derating and wire fill have to be complied with.
With a load of 436 amperes why a 600 ampere CB?
350 KCML is rated at 310 amperes in the 75 degree column for copper. The conductors are only required to be sized for the connected load, plus a bit more.
Why not just trust the electrican and let him wire it?
 
The panel is basically an enclosure for a Variable Speed Drive and control transformer. The panel has 600A trip breaker. This is why I choose 600A to feed the panel. (By the way the panel will be 15 feet from the feeder if that helps.)

It was my understanding the conductors are to be sized to the protection device. That is why I choose (2) 350 per phase. Did I miss something? I have been sizing conductors to the feeder size for a while.

The reason I did no go with the electricians method without question is because an Engineer from Square D told me I had to have each phase in each conduit.

Paul
 
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