addition of neutral to existing feeders to existing three-phase panel

[TobiasKeith]

I have an installation scenario where I am to provide a quotation to install one (1) 500KCMIL THHN conductor for a "neutral" to just one (1) set of three (3) sets of (3) 500KCMIL THHN current carrying conductors that originate from a central distribution switchboard and route and supply power to a distribution panelboard. From this distribution panelboard, we are to install and route in an existing raceway a neutral for a panelboard (this panelboard has just a single set of feeders).
My concern per section 310.4 of the electrical code (2011) is that the distribution panelboard with three (3) sets of feeders should have a neutral conductor in each of sets.
I have consulted with (2) engineers and (1) electrical inspector to seek their interpretation. The customer asks that I fullfil this request and deems one neutral in the distribution panelboard sufficient and will take care of the three-phase/neutral needs of the single set panelboard being supplied with power.
Any thoughts from my fellow electrics out there in weighing in on this? Am I missing something in this request? I have not received the inspection/engineering feedback as of this writing.
Thank you all

 

[infinity]

If I'm reading the question correctly you are correct that you would need a neutral conductor in each of the parallel raceways. If one 500kcmil conductor is large enough for the calculated load then you might be able to get away with a #1/0 in each of the three raceways.

Welcome to the Forum.

 

[texie]

I'm not sure I understand correctly, but if the parallel's are all in 1 conduit you could have just 1 neutral (assuming the load calc supports it).

 

[don_resqcapt19]

I'm not sure I understand correctly, but if the parallel's are all in 1 conduit you could have just 1 neutral (assuming the load calc supports it).

I would really doubt that there are three sets of 500's in a single conduit.