My neighbor the (um) electrician tried backfeeding his house through a 240V receptacle in the garage. The generator is a real old-timer: open frame with cotton cloth insulated wire in the windings. The three-wire output from the alternator is terminated at a three-position terminal board, unmarked and no terminal is grounded to the frame.
Neighbor *guessed* how to connect this to the house ... never bothered to check voltages with a multimeter. Immediately after starting up the generator, he observed that the lights were "real bright". So he shut down and ran a wire from the generator frame to a piece of conduit driven into the ground. Alas, the second startup was like the first and quickly aborted and declared an unsolvable mystery.
Neighbor went into the house, noticed smell of burning insulation everywhere. He filed a claim with his insurance company for damage due to an electrical surge: microwave oven, VCR, two televisions, cordless phone, clock radio, control transformer in furnace, etc. The refrigerator and two freezers were not damaged.
My guess is that he misconnected the genny, putting 240 on one side of the service and zero on the other. The three coldboxes were lucky to be on the zero volt side. But would a light bulb operated at 200% rated voltage just become "real bright" and survive a couple of brief tests or become an instant flashbulb?
ps: This guy really is an electrician ... or at least has been selling his time as such for about 20 years. Seldom gets additional work from old customers though.