On this day: Ontario relay sets off the great blackout, 1965

On the evening of Nov. 9, 1965, a single piece of protective equipment in Ontario set off one of the largest power failures in history, leaving more than 30 million people in Ontario and the northeastern United States without electricity for up to 13 hours.

What happened

At about 5:16 p.m., a backup relay tripped on one of the transmission lines carrying power from Ontario Hydro’s Sir Adam Beck No. 2 generating station in Queenston, near Niagara Falls. The relay had been set too low during maintenance, so a small surge in power flow was enough to trip it, even though the line was carrying far less than it could handle.

The power on that line instantly shifted to the remaining lines, which overloaded and tripped one after another. The surplus from the Niagara stations surged into the interconnected grid in New York state, and within minutes the failure cascaded across the region. Beck’s generators shut down to protect themselves.

Who lost power

The blackout covered about 207,000 square kilometres. In Ontario, most of the province, including Toronto, went dark during the evening rush hour. In the United States it reached New York City, much of New York state, New England and parts of New Jersey and Pennsylvania. Subway riders were trapped underground, and New York City was not fully restored until nearly 7 a.m. on Nov. 10.

Why it still matters

The failure showed how tightly the Canadian and American grids were already tied together, and how one fault could spread across a border in minutes. It led directly to the creation of new reliability bodies to co-ordinate the North American grid, the forerunners of today’s North American Electric Reliability Corporation, whose standards Canadian utilities follow.

Accounts of the exact number of people affected vary, from about 30 million to 35 million.

Sources: Radio Canada International, “History: Nov. 9, 1965, the great northeast blackout”; EBSCO Research Starters, “Power Failure of 1965”; contemporary accounts compiled in public reference works.