NEC grounded conductor requirements

[bilwei]

Application - The Power company has provided a 3-phase 2500 KVA 12470 X 277-480 volt Y-connected step down transformer. This is an industrial poultry processing plant. We need a 3000-amp, 480-volt, 3-phase, 3-wire service from the transformer to a main service disconnect. This service disconnect will feed a remote MLO switchboard. All loads are 480 volt. We do not have any equipment or lighting that will require a neutral. Does the NEC require a neutral (grounded conductor) from the transformer to the service disconnect and from the disconnect to the MLO switchboard because of the power company Y-connected transformer?

 

[don_resqcapt19]

bilwei,

Does the NEC require a neutral (grounded conductor) from the transformer to the service disconnect and from the disconnect to the MLO switchboard because of the power company Y-connected transformer?

If the utility has grounded XO at the transformer, then a grounded conductor is required from the transformer to the service disconnect. The grounded conductor is not required beyond that point, but EGCs are required. See 250.24(C). In this case the grounded conductor, since there is no load on it, will be sized per Table 250.66. See 250.24(C)(1).
Don

 

[raider1]

Take a look at 250.24(C)

Chris

 

[tom baker]

Think of the grounded conductor from the transformer as having white insulation with an imaginary green stripe. Its sized to carry the maxium unbalanced current per Art 220 (not in your case) or carry the ground fault return current back the transformer in the event of a line to case fault, per 250.66
Past your service point the white grounded conductor becomes a green equipment grounding conductor. In either case it there to clear a ground fault.
Must be a lot of chicken processing!

 

[bilwei]

This processing plant is super sized. The work in this discussion is for the Waste Water Treatment Plant only. I appreciate the input from everyone. Back to the main question:

The utility has grounded X0. The feed between the power company transformer and the main service disconnect(MSD) will be (8) parallell runs of 500 KCMIL cu cdrs per phase in eight PVC conduits. Reading from Article 250-24(C)(1) & (2)It leads me to believe that we need a 1/0 conductor in each of the (8) conduits to comply with the NEC requirements for a grounded conductor.

Addressing the feeder between the MSD and the MLO switchboard. From the information posted and as I interpret the NEC. The EGC most be sized as per table 250.122. In this case of a 3000 amp OCP device (this breaker will have GFCI pretection as per the NEC), it is a 400 kcmil cu cdr in each of the (8) parrallel conduits. If I understand correctly, I will not need a grounded conductor between the MSD and the MLO switchboard and that the ECG is all that is required.

What sense does it make that my grounded conductor between the PoCo xfmr and the MSD is a 1/0 conductor and the ECG between the MSD and the MLO switchboard is a 400 kcmil cu cdr.? Unless I misunderstood the NEC requirements. Please fire away. Am I going in the right direction?

 

[don_resqcapt19]

bilwei,

What sense does it make that my grounded conductor between the PoCo xfmr and the MSD is a 1/0 conductor and the ECG between the MSD and the MLO switchboard is a 400 kcmil cu cdr.?

That is just a glitch in the code that comes into play because of the parallel runs. If there were no parallel runs the service grounded conductor would be 500kcmil and the feeder EGC would be 400kcmil.
Don