Electrician's advice needed please

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?

Watts and amps are used to calculate your electricity use/needs. It isn't just the generator that you need to calculate, but also the size of the cord between the generator and the house. Too small of wire and you can't get your electrical across it (it will burn up).

In a previous life, I was an electrician.

This is the sort of thing that, if you need to ask these questions, you are far better served bringing in an electrician to diagnose and put right. Not to put too fine a point on it, but this stuff is dangerous, both because of the shock potential and the fire potential.

In my work as a firefighter, I see a great many house fires that have resulted from "clever" wiring.

Thanks for the feedback.

In my case, it was the original builder and his electrical contractor who finished the basement so the wiring is definitely meeting code. What we failed to do was discuss the watt capacity of my generator and curtail the number of circuits in the emergency board to suit. i don't know how many circuits a 2900 watt generator can handle. I spoke to my BIL who has a similar set-up, also professionally installed; his generator is 5500 watts and works without the GFI tripping.
I will research this some more and talk to an electrician.

A 2900 watt generator kicking out 120v single-phase can handle ~24 amps of output, with a "power factor" on the load of "1". The power factor is a measure of how "irritating" the load is - a purely resistive load like an incandescent light bulb or a resistive oven is "1".

Your normal boring household wall socket is probable on a 15 amp circuit. So not quite two circuits.

A 2900 watt generator is quite small, unless you are just running a couple of lights and some other odds-and-ends. The start-up current if you try to run something nasty (like a motor) might cause it to get grumpy.

Handy resource: https://powerequipment.honda.com/gen...how-much-power

As to your GFI tripping, you need to get that tracked down - it could be something stupid (too much "leakage") or it could indicate a safety issue.

Boring resource:

https://www.cat.com/en_US/consumer/a...-tripping.html

Are you trying to pull too much current thru the GFI. Most GFI's are 15 or 20 amp's. If you are trying to run too many items off the two outlets, that would explain blowing the circuit. The other possibility is one the things your pluging into it is shorted somewhere and that is blowing the circuit. Hope that helps. If you aren't good with electricity, call a pro.

Thanks for the links. That was what I was looking for but didn't know how to phrase my search.