Officials Blame Human Error for the Latest Blow to the Reputation of Metro-North The sprawling shutdown that halted commutes for nearly two hours across Metro-North Railroad on Thursday night was traced to a simple disconnected wire - overlooked by technicians who were trying to replace a power supply unit, transportation officials said. There are two main power sources for the computers that govern train movement on Metro-North from a control center at Grand Central Terminal. One was taken out of service for replacement around 7:45 p.m. on Thursday, in the throes of the evening rush. The second was inoperative because of the disconnected wire. The resulting shutdown filled the terminal with frustrated travelers, and dealt another blow to Metro-North's already diminished reputation. The Metropolitan Transportation Authority, which operates Metro-North, said more than 50 trains were forced to stop, then move slowly to the nearest station if they could. Service on the Hudson, Harlem and New Haven lines began returning by about 9:30 p.m. after a temporary power source was established. Thomas F. Prendergast, the authority's chairman, said that trying to complete the maintenance work during a rush hour was "just uncalled-for," adding that he had "never seen it done" in his nearly four-decade career. He said the work was typically done in the middle of a weekend night, "when you would have the least impact on as few people as possible." Mr. Prendergast's comments came after a conference call with reporters to discuss federal money tied to recovery from Hurricane Sandy. In a statement, he also directed the railroad to assign an independent consultant to "examine how and why these mistakes were made" and recommend appropriate changes. The power failure was the latest in a series of troubles on the railroad over the last several months. On Dec. 1, four people were killed and more than 70 were injured after a Hudson line train derailed in the Bronx. In May, a track foreman in West Haven, Conn., was struck and killed after a trainee rail controller opened a section of track without proper clearance. Other episodes have included a train collision on the New Haven line in May, which injured scores of passengers; a disruption on the Hudson line in July after a freight train derailed in Spuyten Duyvil; and a loss of service on the New Haven line in September after the failure of a Consolidated Edison feeder cable. "When you have to take a breath to complete the list of things that went wrong, it's an indication that somebody needs to take a closer look here," said William Henderson, the executive director of the Permanent Citizens Advisory Committee to the transportation authority. Less than three weeks ago, Metro-North's president, Howard R. Permut, said he was retiring at the end of the month. He will be replaced by Joseph J. Giulietti, the executive director of the South Florida Regional Transportation Authority. Though the railroad has long been known as one of the region's most reliable, Mr. Prendergast allowed during the call that its standing had been compromised. "That's not lost on me personally or the agency," Mr. Prendergast said. And we need to get it corrected and corrected soon.