jaggedben, I appreciate your response. I'm now shifting my discussion from line side to load side connections.
I'm not trying to beat this subject to death (I know there are other threads about it also) but especially with the AC modules just coming to market it's important to come up with a solution for "AC combiner panels". Unfortunately this can't wait until the 2014 NEC or later. In our area the utilities all require an external AC disconnect. Since no one wants to put up multiple disconnects (6 max.), we can't take each inverter to a breaker in an existing load center. If we could, the rules would be straightforward. Therefore anytime we have more than one inverter, we need to use an AC combiner panel. 705.12(D) says in part, "Where distribution equipment including switchboards and panelboards is fed simultaneously by a primary source (s) of electricity and one or more utility-interactive inverters, and where this distribution equipment is capable of supplying multiple branch circuits or feeders or both, the interconnection provisions for the utility-interactive inverter(s) shall comply with (D)(1) through (D)(7)." This is clearly written about using an existing general use loadcenter or panelboard with other branch circuits. I understand that it is by default that the discussions on the subject are applying this to AC combiner panels because there isn't anything specifically written about using a dedicated panel. I also understand that the code panel's rejection of labeling and other means of identifying a dedicated panel would cause a person to use the general rules even though the conductor part is overkill. Whether the solution comes from a manufacturer creating a UL listed AC dedicated combiner or the code panel comes up with a separate section for a dedicated solar panel, we need a better solution. If there were to be a section describing the requirements for a dedicated solar AC combiner panel, I would add an exception that would allow a small amount (10% or ? of the ampacity of the panel) of solar PV related loads along with the multiple power sources for monitoring or weather station sensors. Especially with Enphase, the monitoring receptacle needs to be wired close to the termination of the multiple inverter circuits.
I was fat, dumb and happy before I started researching this subject further. As with other subjects, the more you learn, the more you realize what you don't know.
From all of the opinions that I've seen, it kind of leaves me on the fence. To summarize, my take is that the most conservative approach (with inspectors and the NEC) is to use the 120% rule on the conductors (and of course the busbars) feeding the AC combiner panel even though this will increase the conductor and conduit sizes by quite a bit. On the other hand a lot of installers seem to use the 120% rule on the busbars and then size the conductors for the largest OCPD feeding the conductors. Is that the general consensus?
Thanks to all for your patience with my questions. There aren't many places where you can have a serious discussion about details like this.
Jeff S.