People wait in a Manhattan diner during a massive power outage that hit parts of New York City on July 13, 2019.
CNN  — 

Con Edison blamed their relay protection system Monday for the weekend power outage in New York City, saying the system didn’t operate as designed, according to preliminary findings from the company.

“That system detects electrical faults and directs circuit breakers to isolate and de-energize those faults,” the company said in a statement. “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.”

“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 company added.

Both New York Gov. Andrew Cuomo and New York City Mayor Bill de Blasio called for a full investigation.

“This could have been much worse,” said Governor Cuomo early Sunday morning. “When you’re talking about a city like New York, with a significant piece of the city basically suffering a blackout, that could be a very chaotic situation. We saw the exact opposite, actually. We saw New Yorkers at their best.”

It could take months to investigate why the outage happened, Con Edison President Timothy Cawley told reporters Sunday.

The outage started Saturday at 6:47 p.m., and the lights were back on shortly after midnight, officials said. It mostly affected midtown Manhattan and parts of the Upper West Side. No injuries or hospitalizations were reported.

At the height of the outage, 72,000 customers were in the dark, utility company Con Edison said. It had given a preliminary number of 73,000 – but lowered it early Sunday.

CNN’s Faith Karimi and Steve Almasy contributed to this report.