The Worst Power Outage in U.S. History

Over the years, there have been many significant power outages, but the worst was the Northeast Blackout of 1965. On Nov. 9, 1965, the blackout left more than 30 million people without power for 13 hours, affecting most of the Northeast, including Connecticut, Massachusetts, New Hampshire, New Jersey, New York, Rhode Island, Pennsylvania, and Vermont. The cause of the blackout was human error. A few days before the blackout, a protective relay was incorrectly set on a transmission line near a Niagara generation station in Queenston, Ontario. A “protective relay” is a device that monitors the flow of power through power lines and trips a circuit breaker when it notices an irregular flow of power. The blackout was traced to a maintenance worker who didn’t set the protective relay high enough. With a drop in temperature, customers started using more power to heat their homes, which put a strain on the system and set off a chain reaction. A small surge in power that originated in Lewiston, New York, tripped the relay that was set too low, in turn deactivating a major power line that supplied power for most of Northern Ontario. With nowhere else to go, the power flowed through power lines to New York, where it overloaded those systems too. This all took place in less than 5 minutes.