At 5:16 PM on November 9, 1965, the Sir Adam Beck Hydroelectric Power Station in Niagara Falls, Ontario, experienced a routine power shift. Unbeknownst to plant operators, a protective relay on one of the main transmission lines heading into Toronto had been incorrectly set years earlier. As demand spiked during the evening rush hour, the line hit a load threshold that the relay interpreted as a short circuit.
The relay instantly tripped, disconnecting the line and dumping its massive electrical load onto four adjacent transmission lines. These overloaded lines tripped in rapid succession, creating a catastrophic cascade of power shifts across the interconnected grid. Electrical energy was forcibly rerouted back toward New York State, causing generators across the northeastern United States to lose synchronization with the system frequency.
Within minutes, thermal power plants tripped off automatically to protect their turbines from physical damage, cascading the outage from Ontario across New York, Connecticut, Massachusetts, Rhode Island, Vermont, New Hampshire, New Jersey, and parts of Pennsylvania. More than 30 million people lost electricity, stranding hundreds of thousands in subway cars and elevators in New York City alone. The sheer speed of the collapse stunned engineers, forcing the power industry to completely redesign system reliability standards and create the precursor to the North American Electric Reliability Corporation (NERC).