We are in agreement that without the ground path wired up, it is harder for the GFCI to trip, as seen in the OP's situation. But, the fact that it does when the ground is attached implies there is a system fault somewhere that is allowing power to be diverted to the ground lead when it shouldn't be. Note, if you were to touch or find that errant point, even with the ground disconnected, the GFCI would still trip, as then, there would be an alternate path for electricity. It could go from the chassis of one device to the other if they had the ground and neutral bonded together inside of them.
There is a system problem with one or more of the devices on that circuit that is tripping the GFCI.
I guess I am the one who introduced what now has me confused, as people keep referring to my situation or the condition in my post. But I described 4 different situations in my post, so I never know which one is being discussed. Let me try to clear up the mess I think I have made.
Knows in all situations; Generator has ground bonded to neutral. house has ground bonded to neutral. 3 appliances (Furnace, normally hard wired to house, Freezer chest normally running on GFCI, Ref/Freezer unit not normally on GFCI), Furnace has outlet at it for powering condensate pump.
Using generator as is to back feed house through a 2 way transfer switch will cause GFCI to blow, as a loop of neutral and ground is formed which splits current causing a current difference between hot and neutral. Recommended practice is to either remove bonded neutral and Ground at generator label as such and not use on any construction sites as it is no longer OSHA approved. Or put in a 3 way transfer switch to break the house ground.
The 4 conditions I went through
1) Turned off main, flipped every circuit breaker off. Diconnected ground wire from outlet back to panel at furnace plugged in generator to plug, GFCI popped, (ground wire from outlet went into furnace and terminated at screw attached to frame, no other ground wires internally attached at that screw), removed that ground wire from outlet into furnace, and everything worked fine. -- Not sure why generator GFCI was popping. Furnace does power a DC thermostat???
2) Plugged in 2 extension cords which ran to Freezer and Ref/Freezer. Everything ran fine.
3) Ungrounded furnace plugged into generator, went to add Ref/Freezer and Freezer extension cords Ground plug went in first and the minute it did GFCI popped. -- I read somewhere that plugging in ungrounded and grounded devices into a GFCI outlet can cause it to pop, there was no explanation as to why this would happen. So why does the Ungrounded furnace which works fine alone, and the Grounded Ref/Freezer and Freezer which work fine alone on extension cord, blow the GFCI when plugged in together?
4) I then got two 3 prong to 3 prong addapters, such that the freezer and ref/freezer unit extension cords no longer had grounds and plugged them and the furnace into the generator and everything worked fine. -- Since the devices are plugged into GFCI outlet it would seem if there was a short in one of the appiances makeing the skin hot, the minute it was touched current would flow through the person to the ground they were on and cause the GFCI to blow. The only risk is if you somehow connected the hot and neutral with your body such that the current was flowing through you and returning to the generator, but in this case having a ground wire there would not save you anyhow. Can someone explain the situation where being on a GFCI without ground puts you at risk of shock?
At this point, I think the risk in 4 is minimal, and I really don't understand why what is going on in 1. nor do I understand why 3 causes it to pop. If I could understand what is happening in 1 and get the furnace online grounded I feel pretty good it would solve 3 and eliminate the need to run situation 4. But I also don't know why running ungrounded and grounded devices at the same time on GFCI causes it to pop.