(Bloomberg) -- An almost 50-year-old circuit breaker that caught fire last week and led to a long blackout in Puerto Rico had been properly maintained, the island’s grid operator said. 

Luma Energy said the breaker near Costa Sur power plant was serviced in March 2020 and due to be serviced again in 2023 “per industry standards,” according to a statement the company released late Tuesday. Luma, the manager of the grid since June, previously disclosed the failed equipment was manufactured between 1969 and 1975.

Some Puerto Rico lawmakers had been questioning whether Luma, a consortium of Atco Ltd. and Quanta Services Inc. working with Innovative Emergency Management Inc., followed proper maintenance practices and how the equipment failure sparked a four-day, island-wide blackout.

“While there has been wild speculation made about the causes, the Puerto Rican people, and our customers deserve answers – not guesses,” Luma President Wayne Stensby said in the statement. “All of us at Luma are determined to conduct a thorough and complete investigation, including an independent forensic review of the failed equipment.”

The U.S. Commonwealth has a notoriously fragile and old electrical system and localized blackouts are frequent. Luma took over grid operations from the bankrupt Puerto Rico Electric Power Authority, or Prepa, last year after a public-bidding process. 

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