Okay, so it doesn't in fact bypass the breakers except for any circuit that it's plugged into. I'm guessing that plugging into a 110 outlet will only power some of the circuits in the house?
Through trial and error, he'll end up with a generator like this:
Which can output up to 15 kW.
Earlier, you mentioned plugging into a dryer outlet. Code allows
only one dryer outlet on a circuit, they are isolated circuits - one breaker, one outlet. So you could not plug anything else into
the same branch.
From the dryer, it could feed the rest of the house, but the total current would be no more than the dryer circuit breaker would allow (20 or 30 amps? Maybe 40?) 40A x 220V = 8.8 KW. Each branch would be further protected by its own breaker.
If you are going to have him plug a 15 kW generator onto a 110V outlet, then he could create a fire if he loaded a bunch of other high draw appliances onto that same branch circuit. But again, for other circuits in the house, you'd need to get back to the main panel through that circuit's breakers, so 20 or 15 A max. 20A x 110V = 2.2 KW. Up to that 15 or 20A limit, he could power everything else in the house. Assuming he flipped the main breaker, so he's not trying to power the neighborhood.
Realistically, he should flip all the other circuits to OFF, and then just turn on the circuits he needs to power, to avoid tripping that circuit's breaker and to avoid wasting gas/diesel powering stuff he doesn't care about.
So when I say "branch circuit", think of it as everything that would go dead if you tripped the breaker on that circuit.
Since his generator is rated for higher power than a single 110 V outlet, it would make more sense to power the selected house circuits through a dryer plug.
-ERD50