Is the ATS you're referring to the Onan RSZ series? Although the RSZ is essentially a GE ZTX, Onan/Cummins doesn't offer a switched neutral (or aux LV contacts for that matter) like GE does. This is why I went for the "GE version" of the switch:
I posted some pics of my genny install in a previous post:
https://www.electrical-contractor.net/ubb/Forum1/HTML/002476.html I just didn't want to deal with an inspector or the POCO claiming the generator was still "interconnected" with an unswitched neutral, so I switched the neutral to avoid the possibility of such dispute.
Since this ATS (and the Onan RSZ) is not service entrance rated, a service disconnect will be needed. This is where I bonded the neutral. At the 60A generator disco, the neutral is also bonded (without this, when the ATS switches to the generator, there would be no neutral bond). But keep in mind the main building
ground point is still at the 200A disco.
If I'm not mistaken, some generator manufacturers, like Generac, specify a seperate ground rod for the generator. I don't have my code book in front me, but I believe not having a single building ground point violates code. My concern would be paralell paths, particularly if EMT, IMC, or RMC or even metal flex is used for conduits. Accordingly, I would never use a seperate genny ground.
I believe a system can still be defined as seperately derived, even if it uses a common ground.
Joe
[This message has been edited by JJM (edited 12-02-2005).]
[This message has been edited by JJM (edited 12-02-2005).]