Where to bond??

[Shockedby277v]

What I have currently is a 1000 KVA primary transformer that is feeding 2 services. One is a 1200 amp and one is a 600 amp. We are changing the 1000 KVA primary transformer to a 2000 KVA and re-feeding the 1200 amp and the 600 amp services then adding a 1600 amp service. The services will be located in the main electrical room and a existing primary switch is located inside the electrical room that serves the primary transformer. The 2 existing services AND the existing primary transformer has the grounding and neutral bonded which also provides the grounding system to the 2 services through a ground ring that goes around the property. There is currently no bond to water, ufer or ground rods. The only other path to ground is in the 1200 amp service to steel. There is obviously a parallel path right now.

Since the primary transformer is customer owned it will be covered by the NEC. The job is under 2008. The electrical inspector is using 250.30 and stating it will fall under separately derived systems. So, he wants us to run grounding conductors (AHJ is calling system bonding jumpers) through each conduit to the transformer and bond the frame and sized to 250.66. We remove the bonding jumper from XO. We maintain our bond in each of the 3 services along with our grounding system. We will also bring the ground ring that goes around the property to the frame of the transformer.

Now from the engineer....

He would like us to remove the bonding jumper in the services and leave the bond in the transformer. He would also like us to install grounds in each conduit. These I think would then become equipment grounds??If we go this route I would think our grounding system would have to go back to this transformer??? These 2 questions are not covered in the returned RFI.

Now my question ...

Which method would be accurate? One or both ?? If we bond in the transformer do we change the size of the feeders for any reason?? Do we have to bond at the service?? What code article would point me in the right direction??

I know I didn't include every little detail but I think I covered enough to get what I'm trying to say across. I'm attaching a sketch of what I have.

Thanks in advance.

 

[don_resqcapt19]

The service disconnect is the primary switch. If there is no parallel current path between the transformer and the building, then you would be permitted to bond both at the transformer and at the building switches. In that case, a supply side bonding jumper would not be required in the raceways between the transformer and the building switches.
Given the information in the sketch, there will be a parallel path for current via the primary EGC. That means that the bonding will be either at the switches or at the transformer, but not at both. No matter which location the bonding is installed at, you will need supply side bonding jumpers in the raceways between the transformer and the building switches. There will be a supply side bonding jumper in each raceway and it will be sized per Table 250.66 and the size of the conductors in the raceway.

 

[Electroplaxes]

This is how I was told to do it on similar project I was on.

 

[augie47]

I agree with don in Post 2. (Excellent explanation)
(Post 3 would be applicable IF you did not have the parallel path due to the primary EGC as don mentioned)