• We will be performing upgrades on the forums and server over the weekend. The forums may be unavailable multiple times for up to an hour each. Thank you for your patience and understanding as we work to make the forums even better.

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

Merry Christmas

belkymd74

Member
Location
Raleigh NC
Occupation
Director of Project Development Engineering
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

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
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

Member
Location
Raleigh NC
Occupation
Director of Project Development Engineering
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

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
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.
 
Top