Parallel conductor current imbalance

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Tractorface

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Hello,
I would like to know if there is a standard for the percent current imbalance between parallel conductors of the same phase.

The installation in question involves (6) 500mcm conductors per phase and neutral installed in a Wireway. The run is about 30 feet total and feeds a 2000 A circuit breaker.

When measuring the current on each conductor it appears that two of the conductors in each phase are carrying up to 10% more than other conductors of the same phase. Each of the wires of a particular phase are the same length and terminated with Compression connectors on one end and mechanical lugs on the other.
Any information as to what is normal would be appreciated. Is there any problem as long as no conductor ever sees over 380A?
Thanks
 
Paralleled conductor imbalance

Paralleled conductor imbalance

10% difference in amps between conductors of the same phase is about what I have measured in several installations. Grouping wires together (A, B, C, N) sometimes improves the load sharing by better equalizing the mutual impedances between cables.

In calculating total ampacity of paralleled conductors, I include a 10% unbalance factor.
 
I don't see any problem, as long as each conductor stays at less than its NEC ampacity. But don't you have to derate the ampacity since there are so many in a wireway? (6 wires per phase, 3 phase would be at least 18 conductors, more if you have neutrals.

Steve
 
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