Complex Bus Arrangement

Brendan Registered Users Posts: 7

In the spirit of meeting the requirements of 690.64(B) ( 2008 ), has anyone dealt with issues pertaining to load side interconnections involving switchgear with complex bus arrangements consisting of main bus segments and riser (vert.) bus sections. Generally in such gear there are a multitude of "tap" buses that branch perpendicular to the main bus to supply fixed frame OCPDs (drawout breakers for instance).

I call them "tap" buses because they are certainly not afforded overload protection from the main overcurrent device that is set to trip, at most, at the main bus rating. In the "as-is" intrinsic state of such gear it is very possible to overload the vertical riser bus-work regardless of any PV interconnections.

Take for instance a 3000A main horizontal bus with 1700A vertical riser bus segments. You may see 4x 600AF breakers on that vertical bus section, but it would not be generally acceptable to load up that bus to 2400A as it was deemed that 1700A was the maximum permissible for the designate heat rise of the switchgear.

So, if I can backfeed a solar PV system on the end of the main bus such that 1.2BB <= MAIN + PV holds, I am generally always constrained to violate the 690.64(B) interconnection limits on the vertical bus sections even for 0A of PV backfeed, as the main overcurrent device ahead of us is almost always rated larger than the rating of the vertical bus segments.

Sometimes with these types of project, making a line side connection is a struggle. Has anyone encountered this type of issue before? Would engineering interpretation and AMM be of any value?

Your input is appreciated!