The Long Island Rail Road said equipment breakdowns like one that stranded tens of thousands of commuters Wednesday could recur "at a moment's notice" until the railroad makes permanent repairs to a faulty signal system just outside the tunnels leading into Penn Station.

The power supply feeding the signals at the busy Harold Interlocking rail junction-- and its backup -- inexplicably failed Wednesday morning, triggering a tortuous commute for throngs of LIRR customers. The railroad made temporary repairs in time for the evening rush, but LIRR president Patrick Nowakowski described the patched-up electrical system as "fragile." Permanent repair work was ongoing Wednesday.

"I'll have to keep my fingers crossed," said Stacey Sonbert, 38, of Merrick, who planned to closely monitor social media to see how the LIRR is performing this morning.

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Patrick Connolly of Glen Head said he came home Wednesday evening prepared to work from home on Thursday, but will consult the MTA electronic alerts before leaving home. "I'll check first thing. . . ."

The service meltdown Wednesday included a 90-minute suspension of all trains into and out of Penn Station at the height of the morning rush, and some riders being delayed by as much as two-and-a-half hours, and without much of an explanation.

The problem, which was first reported about 5 a.m., occurred at Harold Interlocking in the Long Island City section of Queens.

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Nowakowski said the signal system there lost its electrical power. A redundant system should have allowed the signals to continue operating, but "in this case, both of them went out," he said.

Despite an early report blaming Amtrak for the problem, Nowakowski said the problems did not "appear to have anything at all to do" with the agency, which owns and maintains the East River tunnels.

The delays -- as long as 143 minutes for one Montauk train -- resulted in large crowds forming at Jamaica station, and stalled tennis fans heading to the U.S. Open at Flushing Meadows on the LIRR's Port Washington line.

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"There are certain areas that are definitely more sensitive to failure in terms of the number of trains and, therefore, customers impacted," said Nowakowski, adding that Harold Interlocking is near the top of that list. "It just goes to show you that there is no room for anything to go wrong during the peak."

After trying different ways to get power to the signal system throughout the day, the LIRR announced about 4 p.m. it had made "temporary repairs" that would allow the agency to run a normal evening rush-hour schedule.

LIRR Commuter Council chairman Mark Epstein said that, compounding riders' frustration was the lack of information from the LIRR -- information that could have made the difference between them choosing to stay on a train or take the day off.

"We have people that have been sitting on trains for two hours. That's not a delay," Epstein said. "If people know what's going on, they're very understanding."

Adam Balaban, 41, of Bethpage, was delayed nearly two hours getting to Penn Station -- including during a one-hour stop at Merillon Avenue. All the while, he said train crews "weren't holding back anything," but also didn't have a lot to say.

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"The conductors really had no idea what was going on. It was pretty much, 'Wait and see,'" Balaban said. "We didn't know what we were doing."

LIRR marketing and public affairs vice president Edward Dumas said the agency "mobilized" as soon as it learned of the problem, and did its best to share with customers "all the real time information that we have."

"You could not create more pressure if you tried," he said.

In the first half of 2015, the LIRR reported 969 delays -- a 33 percent increase from 729 delays in the first six months of 2014.

Gov. Andrew M. Cuomo, at an unrelated Greenwich Village event, said upgrades to the transit system, including the LIRR, must be made and the need is urgent.

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"It's a very big system, and issues come up," he told reporters, saying investing in the Metropolitan Transportation Authority's "robust" capital plan is important to avoid "continued issues."

With Emily Ngo, Joan Gralla and Maria Alvarez