I've heard that a South African fossil power-plant had bit of a problem years ago when they tried to bring a new generator onto the national grid. Some hairless ape (i.e. human being) made the switch when the cycle was 180° out-of-phase. The entire generator apparently took off and landed on the opposite bank of the river the station was based on!

(Another power-gen technician I spoke to said that he'd never heard of that story, but had seen generator shafts that broke under similar circumstances. So it may just be urban legend...)