The utility said the finding followed an inspection of equipment and preliminary review of system data.
Con Ed said the relay protection system detects electrical faults and directs circuit breakers to isolate and de-energize those faults.
Con Ed issued a statement that read in part:
"The relay protection system is designed with redundancies to provide high levels of reliability. 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 failure of the protective relay systems ultimately resulted in isolation of the fault at the West 49th Street transmission substation, and the subsequent loss of several electrical networks, starting at 6:47 p.m.
Based on our experience with the transmission and distribution system, we initially believed the 13,000-volt cable fault was unrelated to the transmission disturbance. While the cable fault was an initiating event, the customer outages were the result of the failure of the protective relay systems."
In all, six networks were taken out of service by the failure, either during a domino of cascading events or proactively by Con Edison, because they were about to fail
New York Gov. Andrew Cuomo has directed a state agency to conduct an investigation into the blackout that left a large portion of Manhattan without electricity
Con Edison officials say the blackout happened at a time when New York was using less power than usual, so the outage had nothing to do with demand on the electrical grid.
The utility company insists it is prepared for a time of higher demand, like one expected this week as the temperatures rise. Officials said engineers are "diligently and vigorously" working to pinpoint the cause of the blackout and determine why backup plans in the system designed to prevent this type of cascading outage failed, but it could be weeks before there are answers for what officials call an extremely rare event.
"We do expect there to be power outages," Con Ed spokesperson Mike Clendenin said. "With any heat wave, you're going to have power outages. They happen. But our crews are ready to respond to anything, to keep them small and isolated, and to get the power back on as quickly as possible."
The outage affected several additional blocks and thousands more customers than initially thought.
On Saturday, Con Ed said the outage zone stretched from 42nd to 72nd streets and from the Hudson River to Fifth Avenue. On Sunday, the company revised that parameter, saying the outage was even wider and stretched as far south as 30th Street.
Carl Sormilic was working on the patio of the popular Smith Restaurant at Lincoln Center on Saturday night.
"Next thing I know, it turned full black out," he said.
Just like that, there was no power, meaning it was time to shut down.
More than 72,000 customers were in the dark, meaning tens of thousands more people were affected. Crews responded to 400 stuck elevator calls, subway trains were halted, and there was confusion on street corners.
"I was worried it was a safety thing," subway rider David Sjakirov said. "People have to go to the bathroom. We need food, we need water. You have people pacing around because their legs were cramping up."
Even Madison Square Garden went dark -- right in the middle of a Jennifer Lopez concert. JLo has reschedule the concert for Monday night and vowed to give her fans their money's worth.
Concertgoers can bring their original tickets for admission to the show.
Senator Charles Schumer is now calling on the Department of Energy to conduct a full investigation, saying Con Ed has improved but still has a long way to go.
"Is Con Edison putting enough money with infrastructure so this doesn't happen again?" Schumer said.
While the exact analysis of the cause could take weeks, even months, people were just happy the outage was much shorter than others before.
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