The basic concept is that since you have two sources, a panelboard could be overloaded if the customer somehow draws more load than the service would carry. When does anybody's main breaker trip simply because they used to much power? Hardly ever, but the code is extra conservative on this. 705.12(B) [2017 NEC reference] contains various rules on how you can do it.I appreciate the responses fellas , thankfully there's no law against educating a redneck spark
But here's one that turns my head around ......
the PV guys come in and do their thing, then determine the panel is too small, by too small i mean the buss
they'll have me place a 200A MLO into a 100A (meter/100A main) system for this
So we end up with a 200A MLO off a 100A service , i just can't 'get' why the focus is on the panel being inadequate when the the rest of the serive is ok?
~R (brain fried in vermont)J~
200A on a 100A service seems like overkill for most situations in my experience, since a 100A OCPD in a 125A panel leaves room for 50A of solar under one rule, which is usually way more than enough. But maybe you've encountered some solar bigger systems, or maybe they're just trying to give themselves maximum flexibility.