Parallel Runs in Multiple Conduits

FaradayFF

Senior Member
Location
California
Hello,
I have circuits consisting of multiple runs of parallel cable. I've got 3x500kcmil per phase. I know for the sake of minimizing magnetic imbalance, you want to bundle one conductor from each phase. Can I install two bundles in a conduit, or would it be preferable to have a dedicated conduit for each bundle- 3x4" conduits, each 4" conduit containing 3 conductors.
Thanks for your advice.
EE
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
310.10(H)(3) says no to 2 sets in one conduit and 1 set in another: "Where run in separate cables or raceways, the cables or raceways with conductors shall have the same number of conductors and shall have the same electrical characteristics."

You could got to 4 smaller sets in two conduits if the terminations aren't a problem.

Cheers, Wayne
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
I agree with Wayne. If you had 4 parallel conductors per phase, you could have 2 in each of 2 conduits. But you cannot divide 3 parallel into 2 and 1.

Also remember the number of current carrying conductors in each conduit and derating requirements.

Still when calculated out it often makes sense to have more than 1 three phase set in each conduit.

Jon
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
Is it still the case where paralleled conductors cant be more than 6" difference in length. If so that may be a factor.
As far as I know there is no specific tolerance given. Parallel conductors must all be the same length.

Of course it is impossible to make them all exactly the same length, but code doesn't say anything about how close is close enough.

Jon
 

Carultch

Senior Member
Location
Massachusetts
310.10(H)(3) says no to 2 sets in one conduit and 1 set in another: "Where run in separate cables or raceways, the cables or raceways with conductors shall have the same number of conductors and shall have the same electrical characteristics."

This would mean that if you have a prime number of sets, then you would either need 1 raceway for every set, or the ability to put all sets in the same raceway. All sets in one raceway is very unlikely for 3 or more sets. A more likely example where you would see this, is with all sets in one cable tray.

An even number of sets could be built with 2 sets in each conduit, such that the number of conduits is half the number of parallel sets. A triplen number of sets could be built with 3 sets in each conduit, albeit unlikely that you would see this in practice.
 
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