The report by the Metropolitan Transportation Authority's inspector general says workers used the wrong connector in installing computer equipment. That led to an electrical surge that shut down trains west of Jamaica.
When the replacement part failed, it said, errors by the LIRR and the company that designed its $56 million signal system made the situation worse.
The MTA said in a statement that the report was "very helpful as we re-examined our procedures and capabilities."
The lighting strike on Sept. 29 nearly brought the railroad to a halt, stranding thousands of passengers on trains for hours.
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