12 kw is 50 amps at 240 volts so that is the rating of the generator and you can connect 80% of that. If he wants to run the whole house he needs a bigger generator. So what is the solution? Take the most essential loads like the fridge, some lights, any pumps essential to sanitation or flood protection possibly. Add a bit of heat for one room and a few convenience outlets for the wireless phone and a hot plate and you are getting to the limit. The load center must be connected through an approved transfer switch with a source from the regular panel and 1 from the generator. Both sources would have a 50 amp breaker ahead and feed a 60 or 100 amp loadcenter through the transfer switch. The grounding at the generator must be checked to ensure the neutral is not grounded as most transfer switches will have a continuous neutral.
