Grounding of Main SwitchBoards

[Samardas]

I am designing a system with two transformers coming out of one feeder manhole from the Utility company, one for a 2000A service and the other for a 1600A service. In the design I showed (5) 4"C (PVC-non metallic) with 4X600AWG and one (1) #3/0 Gnd. in each conduit for 2000A and (4) 4"C with 4x600AWG and one (1) #3/0 Gnd. in each for 1600A service. In the Main Switchboards, I showed Neutral and Ground Bus connected and then connected to the ground ring.

But the contractor says since they have a ground ring and a cold water pipe, which they are using for the transformer grounding, there is no need to run a #3/0 through each conduit as I had suggested. Instead they want to connect the MSBs' Neutral and Ground Bus to the same ground ring. When I look at the NEC (2013 and 2014), I get little confused as to what is acceptable. What are your thoughts? Diagram attached for your ref. Thanks a Lot for your help!!! (Although, I am trying to learn as fast as I can, perpetually I get confused when it comes to grounding:?)

 

[wsbeih]

I am designing a system with two transformers coming out of one feeder manhole from the Utility company, one for a 2000A service and the other for a 1600A service. In the design I showed (5) 4"C (PVC-non metallic) with 4X600AWG and one (1) #3/0 Gnd. in each conduit for 2000A and (4) 4"C with 4x600AWG and one (1) #3/0 Gnd. in each for 1600A service. In the Main Switchboards, I showed Neutral and Ground Bus connected and then connected to the ground ring.

But the contractor says since they have a ground ring and a cold water pipe, which they are using for the transformer grounding, there is no need to run a #3/0 through each conduit as I had suggested. Instead they want to connect the MSBs' Neutral and Ground Bus to the same ground ring. When I look at the NEC (2013 and 2014), I get little confused as to what is acceptable. What are your thoughts? Diagram attached for your ref. Thanks a Lot for your help!!! (Although, I am trying to learn as fast as I can, perpetually I get confused when it comes to grounding:?)

You got a non metallic conduit. The way i see it you need to keep the #3/0 GND to comply with supply side bonding jumper NEC requirement.

 

[infinity]

If the conduits contain service entrance conductors you do not need an EGC in each raceway. Installing one would put the EGC's in parallel with the neutral which would create a parallel path for the neutral current and a violation of 250.6(A).

 

[Samardas]

Grounding of Main SwitchBoards

So, what is the verdict? Should I use 1x3/0 grounding conductor through each conduit or ground the system separately to the same ground ring without using a separate 3/0 conductor in each conduit. Not quite clear from the NEC.
Thanks a LOT!
Samar

 

[ActionDave]

The NEC does not start until the service disconnect. You don't use a separate equipment grounding conductor between the service disconnect and the utility transformer.