A few weeks ago I had a service call to a house where the woman had some lightbulbs blow up some only dim her surge strips melt and her fluoresant ballests burn up. In her case the neutral wire(old aluimium seu) disintagrated and could not carry the load of the furnace, refig, etc motor load starting. This sent 120v back thru the neutral and with no place to go, back thru the via the neutral to the circuits on the other phase p putting 240v across phase to neut. Took a while to find it because the disintagrated cable was hinden bey the outer jacket. I would check you gen set cord to make sure that it is made up proporly, as even from the factory it could be bad or mis connected neutral. I would also check the gen set itself with a meter and a high watt electric heater testing each outlet to make sure your gen output doesn't scew up under load.