Puerto Rico’s Energy Bureau concluded that the April 16, 2025 island-wide blackout was caused by a combination of technical failures in the electrical system, including rodent damage to protection wiring, deficiencies in backup systems and vegetation management problems. According to the report, the blackout began at 12:38 PM, when a tree near transmission line 50100 caused an electric arc.
The initial fault worsened because a switch at Cambalache did not respond as it should, allowing the fault to remain active in the system. The investigation found that the cable responsible for transmitting the signals that activate the switch had been damaged by rodents inside a conduit. This kept the protection mechanisms from correctly sending the orders needed to disconnect the affected line.
The Energy Bureau also reported that the design of the protection system at Cambalache relied on a single cable for multiple safety functions, eliminating the redundancy that should have existed to respond to a fault. In addition, one of the main protection schemes was out of service because of communication problems. In its final report, the regulator determined that LUMA Energy’s preventive maintenance and inspection practices were insufficient to identify critical conditions inside electrical equipment, and it ordered the company to strengthen its inspection and maintenance protocols.