NEC 310-4c does not allow conductors to be different lengths in parallel installations. Obviously it is difficult to ensure the conductors are indeed the same length due to conduit routing, 90's, etc... Theory says if they are not the same length, current will be different in the conductors. Similar questions have been posed here before, but none of the answers I found here were in agreement with each other, and none seem very clear on how to calculated this.

We have a 3000 amp circuit being fed with (8) runs of 4x500 Kcmil in each conduit. This paraticular installation is such that it is impossible to complete this installation with all of the conductors the same length. So, we need to calculate the current in each conductor to see if the installation will work, or if we need to change the installation.

The longest run is 126 ft., and the shortest run is 119 ft. I need to calculate the maximum current in the conductors to make sure we do not exceed allowable ampacity.

Does anyone out there have a complete calculation to do this?

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