Bonding Service in a Manual Transfer Switch Remote to a Building

[scotteng]

We design a chain of banks in Florida that utilizes a manual transfer switch (MTS) with camlocks for connecting a portable generator. The MTS is mounted on a freestanding structure next to, and downstream of, the utility meter. The location of the MTS support structure varies and can be near the building or somewhat distant. The MTS contains the service main disconnect and as such, we ground and bond the service neutral at this point. An EG is then run with the feeder conductors from the MTS to the building main panel, which also contains a main disconnect for the building. The building gets a pair of ground rods and all available grounding electrodes at the building are tied together and bonded to the EG, but NOT to the neutral. We are treating this as a building supplied by a feeder per 250.32.

An field inspector has given us a comment that we need to tie the ground rod at the MTS to the grounding electrode system of the building with a separate GEC. He is stating that the design we show utilizes the EG that is run with the feeder as a GEC, which is prohibited. I see this as one building fed from another which does not require a separate GEC run between buildings. Thoughts? Is there a minimum distance where the ground rods are close enough that they should be tied together?

 

[Smart $]

... I see this as one building fed from another which does not require a separate GEC run between buildings. ... Is there a minimum distance where the ground rods are close enough that they should be tied together?

None that I'm aware of. I agree with your assessment.

Did or will the inspector provide a section reference (other than 250.121).

 

[augie47]

I also agree with your method.

There is no specified distance, but, one might reason, if the two ground rods are close enough to be tied together then its' one premises and rods at the building aren't necessary

 

[Smart $]

I know you mentioned 250.32, but see 250.32(D) specifically, because it requires only an EGC.

 

[scotteng]

Did or will the inspector provide a section reference (other than 250.121).

Yes, secocond hand via an RFI from the contractor...250.4, 250.24(A)(1), 250.24(A)(5), and 250.121. I didn't feel any of those sections fortified the inspectors arguement.

 

[Smart $]

Yes, secocond hand via an RFI from the contractor...250.4, 250.24(A)(1), 250.24(A)(5), and 250.121. I didn't feel any of those sections fortified the inspectors arguement.

I agree. Assuming proper installation...

250.4: EGC establishes "Effective Ground-Fault Current Path"

250.24(A)(1): MTS is the service disconnecting means (w/OCP and SUSE). Grounding electrode connection is made at that point. GES is made up of two ground rods not less than 6' apart, as no other electrodes exist at the MTS supporting structure.

250.24(A)(5): EGC, GES, and other non-current-carrying metal parts are isolated from the grounded conductor at building (load-side grounding connections). See also 250.32(D)(1).

250.32(D)(2) requires only an EGC between remote disconnecting means and building served.

250.121: Given all the above, 250.121 does not apply.