Neutral conductors in cable tray for parallel feeder

[DeividHN66]

Hello everyone, first time posting here.

I have a question regarding parallel feeders. In a design presented by a client, the ungrounded conductors are divided into three parallel conductor sets, but the neutral is only installed in two sets, sized for a lower ampacity. There is also a single equipment grounding conductor.

Before I proceed, I want to confirm whether this complies with the NEC.

The entire run between equipment is installed in cable tray, including the vertical drop to the equipment. I understand that only one equipment grounding conductor is required for the feeder in the tray, but I am not sure about the neutral.

Is it permissible to install only two (2) neutral conductors in parallel, or must the neutral also be run in three (3) conductors just like the ungrounded conductors?

Any guidance or code references would be appreciated.

 

[don_resqcapt19]

I was going to suggest 392.20(C), but it seems to stop short of requiring a neutral in each group.
If I was designing this and the neutral had a lower required ampacity, I would install 3 neutrals, but use a smaller conductor for the neutral.

 

[DeividHN66]

I was going to suggest 392.20(C), but it seems to stop short of requiring a neutral in each group.
If I was designing this and the neutral had a lower required ampacity, I would install 3 neutrals, but use a smaller conductor for the neutral.

Based on your comments, I understand that the best practice is to use the same number of ungrounded conductors and neutrals. However, there is no article in the code that explicitly prohibits this.
I would prefer to keep the original design and not have to submit changes.

Thank you for your time.

 

[winnie]

In parallel installations, the general requirement is that all parallel conductors have the same electrical characteristics, meaning the same length, the same insulation, the same conductor material, and the same electrical characteristics of the enclosing raceway. Note that one phase doesn't have to have the same characteristics as another phase; because those aren't in parallel. The 'same characteristics' applies to each phase (and neutral) separately.

In metallic conduit, one of the aspects of electrical characteristic is the magnetic coupling to the other phases. Because of this, each separate conduit in a parallel set must have the same conductor arrangement. You don't need to have the same number of conductors in different phases, but each conduit must be electrically the same as every other conduit in the set. In particular you can't have some conduits with a neutral conductor and some without.

Going to the original post, if you had three conduits with conduit 1 ABCN, conduit 2 ABCN, and conduit 3 ABCG, you would have a violation of the basic rules for parallel conductors. The conductors in conduit with the neutral would have different characteristics from those without. 310.10(G)

But you are asking about cable tray an that is different, because in one real sense all of the conductors are in the same bucket. You have 1 bucket holding AAABBBCCCNNG. I think that the grouping requirements for parallel circuit conductors in the cable tray 392.20(C) might be the prohibition for your desired install. Your cable tray contains 'groups' and the 'groups' would be different (with or without neutral). I am not current on article 392, so recommend that you double check that text.

 

[jap]

I guess I was fortunate.
All of our installs in Cable Tray was actual Tray Cable itself, not individual conductors.
In this scenario we would have installed (3) cables, and, each cable would have been the same containing ABCN&G.

I can see where it could get very interesting when trying to decide what to pull when pulling in individual conductors vs. tray cable for sure.

Jap>