"The project should have been analyzed for risks and redundancy before it began, and it should not have been performed when thousands of customers were trying to get home in cold weather," MTA Chairman and CEO Thomas F. Prendergast said.
Governor Dannel P. Malloy called the situation "frankly, unfathomable."
"I expressed my anger and frustration in a call this morning with MTA CEO Tom Prendergast, asked him for a full explanation and an action plan to prevent any recurrence," Malloy said in a written statement.
According to the MTA, the computers that run the signal system lost reliable power at 7:45 p.m. when one of two main power supply units was taken out of service for replacement.
Technicians performing the work did not realize that a wire was disconnected on the other main power supply unit. That mistake destabilized the power supply system for more than an hour until a backup supply could be connected.
"Metro-North customers deserve better, and I extend my sincere apology to all of them," Prendergast said.
Prendergast says he has ordered Metro-North to bring in an independent consultant to examine how and why these mistakes were made, and to recommend any changes.
More than 50 trains were forced to halt for safety reasons when the signal system went dark. They were slowly moved to the closest station. Trains were not allowed to proceed through switches until signal maintainers could respond and manually ensure the switches were lined up correctly, which delayed some trains further.
The commuter railroad spent the entire night struggling back from the outage that lasted nearly two hours on all three lines running out of Grand Central Terminal.
The last stretch to be restored was the Danbury branch on the New Haven line. People at stations outside of Manhattan had the toughest wait, often with no heat and no information.
Metro North commuters headed home on Friday were not happy, especially after hearing the MTA admit to what caused the shutdown of the railroad last night.
"There were like no trains running. There were so many people in here so I ended up taking the subway," Pancia Davis said.
"It was frustrating. I didn't get home till about midnight last night," said another commuter.
What commuters now find most surprising and what the MTA chairman says he's never seen before in his railroad career is the scheduling of this maintenance work during a peak period.
"We had someone make a decision to do a maintenance activity in the heat of the evening rush hour, which is uncalled for," he said.
Most commuters had similar reactions: "That's outrageous. It really is outrageous," one said.
"We don't blame people for being unhappy today. We are not happy today. We are pledging a full investigation into what happened," MTA spokesperson Adam Lisberg said.
Amtrak also was affected by the suspension.
Metro-North serves 281,000 riders a day in New York and Connecticut.
It has experienced a spate of problems in the last year, including a derailment in the Bronx that killed four passengers.