Neutral to Ground Bonding Location for Separately Derived System with Multiple Generators

[belkymd74]

I've got an AHJ telling me that if I have multiple generators tied to an essential system paralleling switchboard that feeds multiple 4P ATS(s) as a separately derived system, that I need to bond at each generator location per NEC 250.30 versus bonding once at the essential switchboard paralleling bus. My thought has always been that multiple bonds can create objectionable circulating current and GF detection issues and is not desirable. It looks like the NEC allows the bonding to be at the essential switchboard paralleling bus starting in the 2020 code but this AHJ is enforcing the 2017 version whereby that doesn't seem to be allowed. Interested to hear your thoughts?

 

[jaggedben]

What part of 250.30 is the AHJ citing and what is their reasoning? If your generators are paralleled you have one separately derived system. The generators (plural) are 'the source'. I don't see anything in 250.30 that says you need to have more than one system bonding jumper in this situation.

 

[belkymd74]

I agree 100%. The AHJ is saying that a N/G bonding jumper must be located at each generator between the alternator source and first means of disconnecting as described in that section. Does the code convey that paralleled generators shall be treated as one somewhere in the code. I'm looking now.

 

[jaggedben]

I agree 100%. The AHJ is saying that a N/G bonding jumper must be located at each generator between the [alternative] source and first means of disconnecting as described in that section. Does the code convey that paralleled generators shall be treated as one somewhere in the code. I'm looking now.

Where are the disconnecting means for the generators? Do they all come together at the switchboard or are there disconnects at each generator.

 

[belkymd74]

They are at the gens and at the paralleling board.