When my downstairs was finished, I included a second circuit board wired to am outlet outside to turn to alternate power from my generator as a backup for longer term power outages. I shut off the main board and once that is locked off, I can turn on a limited number of circuits - fridge, freezer. lights in kitchen etc.
During the last ice storm, I tried to power with my generator without success. The GFI fault light came on. I could get a lamp lit from an additional outlet on the generator once I reset the GFI. I had my handyman check my steps and he found nothing.
Today, with the strong winds, the power went out again so I tried again. Checked with the lamp which came on but as soon as I plugged the cord to connect the generator with the outside outlet linkage to the in-house board, the GFI tripped.

My question, if you are still with me, is - is there a minimum size generator for such use and is mine too small? We used it on the farm to run the sump pump and some lights running a cord from the outlet on the generator directly to the sump pump and a few lights.

How does one calculate the generator size to meet the demand of limited house circuits or is this a question for a visit from an electrician?