Qty of current conductors in EMT, industrial design

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fastline

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Engineer
I am working on a build out design for an industrial application with several 3 phase machines. I am curious if you guys typically just run 3 conductors as a dedicated conduit, or prefer to go up to 6 conductors and take the 20% derate hit? I'd sure like to keep the conduit clutter to a minimum.

Also, we have some 30-40kva equipment to connect. In the past we have always used Copper conductors, but can anyone see a reason not to consider Aluminum? It will certainly make a different in the conduit sizing so I need to sort that one out.
 
Since you can start with the 90 deg column for derating purposes when more three ccc, I don't see much benefit to not running 6 ccc in a conduit. That seems to be the sweet spot.

I see nothing wrong with using aluminum conductors.i think the smallest size available is #6 though.
 
Curious why the sweet spot would be 9 ccc? I suppose to some extent, it might become overly expensive in conduit size to accept a large bundle of Al conductors? I am open to it, just asking. That's why I'm here. Trying to make a plan.
 
Gotcha! I guess I need to get schooled here, as I thought if any part of the system was only 75c rated, you could only use 75c ampacity? Could anyone point me to the code on that? I will need to watch Vdrop so that might force a larger conductor in any case.

Most equipment will be at 208V but will have to set a couple 480/208 Xfmrs. Those would get dedicated raceways.
 
fastline said:
Gotcha! I guess I need to get schooled here, as I thought if any part of the system was only 75c rated, you could only use 75c ampacity? Could anyone point me to the code on that? I will need to watch Vdrop so that might force a larger conductor in any case.

Most equipment will be at 208V but will have to set a couple 480/208 Xfmrs. Those would get dedicated raceways.
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The final ampacity of the conductor cannot exceed the lowest ampacity rating of any part of the circuit. That does not limit the use of the 90°C ampacities for the purposes of ampacity adjustment and/or correction.
110.14(C) Temperature Limitations.
The temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected termination, conductor, or device. Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both.
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don_resqcapt19 said:
The final ampacity of the conductor cannot exceed the lowest ampacity rating of any part of the circuit. That does not limit the use of the 90°C ampacities for the purposes of ampacity adjustment and/or correction.
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Outstanding! very much appreciated! I don't think this has come up much for me because Vdrop ends up driving the design anyway.

I will apply this in the layout and see if it helps us anywhere.
 
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