Wayne,

So how are the service entrance conductors sized? If the ampacity of
the service conductors is less than the sum of the ratings of the main
breakers on the three main panels, then the only thing protecting the
service conductors from overcurrent is the statistical unlikelihood of
all three services drawing maximum power simultaneously?

I installed a 200A panel in our garage, and another 200A panel in our
house. Each panel is supplied with three 4/0 aluminum conductors that
connect to the power companies junction box. Our pump house only has two
breakers, 20A for the pump, and 15A for the lights. It has been many years
since I hooked that up, but I think I used three 1/0 copper conductors for
that panel.

The cable between the junction boxes and the transformer at the road was
provided and installed by the power company. I wasn't here when they hooked
us up, so I don't know what kind of cable they have on their side. When we
hooked up our house, I asked the power guy about the cable, and he made a
comment that their cable was a little undersized to be powering all three
buildings. But he said that was done routinely a few years ago before they
started running load calculations. He said it wasn't a big problem, since
we were unlikely to max out all panels at once, but we may notice dimming
lights if I was powering up equipment in the garage while the heaters were
running in the house or something.

But, in the 15 years or so we have lived here, I've never noticed any
problems with dimming lights, or any other signs of too much current draw.

Anthony