Con Edison workers on Sunday examine electrical infrastructure under West...

Con Edison workers on Sunday examine electrical infrastructure under West End Avenue at West 64th Street in Manhattan, a day after a widespread power outage in parts of the borough. Credit: Charles Eckert

A system designed to detect and isolate electrical faults failed at the West 65th Street power substation and caused Saturday’s disruptive blackout in Manhattan, Con Edison said in a preliminary report Monday.

The relay protection system was supposed to direct circuit breakers to de-energize problem points, but why it didn’t and why backup systems did not kick in are still under investigation, the utility said.

“The relay protection system is designed with redundancies to provide high levels of reliability,” Con Edison said. “In this case, primary and backup relay systems did not isolate a faulted 13,000-volt distribution cable at West 64th Street and West End Avenue.”

The outage affected nearly a quarter of a million people when several electrical networks went down at 6:47 p.m. Thousands of people were trapped in the subway system and Broadway shows were canceled, but many rose to the calamity, including citizens who directed traffic and actors who entertained on the sidewalks.

Con Edison said power to half the customers affected was restored in less than three hours and within five hours for the rest.

Officials have berated the utility and called on regulators to investigate the utility and the outage.

“We remain in contact with the utility as answers unfold and they are aware of our request for the feds to also investigate the outage,” said Angelo Roefaro, spokesman for Sen. Charles Schumer (D-N.Y.), who has asked the U.S. Energy Department to look into the utility.

A forecast of days of 90-degree weather for week’s end in New York City could lead to power outages, Con Ed officials said Monday.

“We are staffing up for the hot weather later this week,” utility spokesman Bob McGee said. “When there is very hot weather like that, we often get localized outages, especially on the third day of 90-degree weather. That shouldn’t be confused with blackouts like the incident we experienced over the weekend.”

Gov. Andrew M. Cuomo, who called the breakdown “unacceptable,” has directed the state Department of Public Service to investigate. His office did not immediately comment on Con Edison’s preliminary findings.

Mayor Bill de Blasio said in a statement: “While I appreciate that Con Edison released their preliminary findings so quickly, I am troubled that one of the few factors Con Edison initially ruled out, the 13,000-volt cable, has been determined to be the catalyst of the outage. . . . We will continue to push Con Edison for a full accounting of this incident to ensure they are taking necessary steps to protect all New Yorkers.”

Con Edison said it has been inspecting and testing transmission equipment and analyzing the “large volumes of data” and ruled out transmission equipment as part of the problem.

McGee said the utility regularly tests its equipment, especially at the onset of summer and of winter. He said the age of the components at the substation was not a factor in Saturday’s cascading failure

“Our analysis of data and testing of the relay protection equipment is continuing and will provide more insight into why the system and its multiple redundancies did not operate as designed,” the utility said in its findings Monday.

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