A sub-panel, splitting off the 'backed up' circuits from the rest of the house is not a 'work-around,' it's a perfectly legitimate form of 'load shedding.' Then the question becomes one of sizing the genny to the sub-panel.
And, again, the specs of the generator companies come into direct conflict with the 'method' espoused by some in the other thread, a method that seems to be what the code language wants.
Let's say I just split off my well, sump pump, refrigerator, gas furnace, and a couple light/receptacle circuits off to this little panel. Just try finding a 30- amp panel with enough spaces; you're almost certain to have a 100-amp panel. Chances are, the lugs won't even secure #10 wires. The end result is very likely to be at least a 50 amp breaker feeding that panel.
If you size the generator to that breaker, you'll have twice as much generator as you'll ever use. I didn't say 'need,' because this is a completely voluntary system; you don't "need" any generator at all.
So, what's the problem with having a big generator? Simply put, the generator starts breaking things if it's not operated fairly regularly under nearly a full load. Often generators will be installed to automatically operate for a period every month for this purpose.
When the generator 'exercises,' one of two things happens. Most often, the transfer switch automatically switched the house over to generator power for a while. If you have a 30 amp household load being powered by a 100-amp (25kw) genny, that genny is not being properly 'exercised.'
The other way to 'exercise' a genny is to use a 'load bank.' A load bank is simply a series of giant toasters, which progressively switch on until the genny is fully loaded. In our example, the 30 amp house would be supplimented by 60 amps of the 100-amp load bank operating. That's a lot of heat - and in a residential setting, I would have concerns about grass fires, etc.
