SAN JUAN – A massive power failure at around 10:30 a.m. Wednesday morning left Puerto Rico Electric Power Authority (Prepa) throughout the island without service. Deputy Director Justo González said during a press conference that a major powerline was impacted by an excavator while a tower that had collapsed was being removed.

González said a Cobra Energy contractor, Texas-based construction company D. Grimm, was to blame for the incident, as well as for a major outage last week, adding that Cobra was halting the firm’s work on the island.

“I have suggested to the PREPA Board of Directors that they cancel the contract with the Cobra subcontractor who is directly responsible for this power outage. This is the second power failure that has affected the people of Puerto Rico in less than a week,” Gov. Ricardo Rosselló said in a statement Wednesday evening.

“This incident denotes the need to transform PREPA into a cutting-edge, modern and robust corporation. Microgrids are the only system currently providing energy to the people of Puerto Rico. This is another example of why Puerto Rico’s energy infrastructure needs to incorporate new forms of power,” he added. “I am committed to push for and enact trailblazing reforms that will ensure thetransformation of our energy sector and give our people a state-of-the-art electricpower system as we rebuild a stronger, more resilient Puerto Rico.”

In an statement earlier, the utility said the failure was registered in one of line 50700’s (230 kilovolts) phases. The transmission line runs from the Aguirre complex in Salinas to the AES plant in Guayama.

“Our technical personnel is inspecting this line to determine the causes of the failure. The restoration will be gradual, as the units begin to generate. We expect that our previously energized clients will have service in approximately 24 hours. If a major complication arises, this period may be extended up to 36 hours,” González added.

Prepa said its priority was to establish service in critical areas such as hospitals, the Luis Muñoz Marín International Airport, Aqueduct & Sewer Authority pumps and banks. Afterward, it would focus on industries, businesses and residences.

The island-municipalities of Vieques and Culebra continue to have service, as well as the microgrids of Charco Hondo in Arecibo and Daguao in Naguabo, according to Prepa.

“Unofficial [:] fault originated in Central Costa Sur and affects Aguirre and since more than 900 megawatts dropped the entire system was affected and the system was protected and left out of service,” the president of Prepa’s Irrigation & Electrical Workers Union (Utier by its Spanish acronym), Ángel Figueroa Jaramillo, tweeted minutes after the event.

He said Guayanilla’s Costa Sur, Peñuelas’ natural gas-fired EcoEléctrica, Salinas’ Aguirre, Cataño’s Palo Seco, Arecibo’s Cambalache, and the Mayagüez and San Juan powerplants were down.

The union leader compared Wednesday’s blackout with the one on Sept. 21, 2016, which left every Prepa customer without service. Then-Gov. Alejandro García Padilla declared a state of emergency in Puerto Rico. In that event, the grid took more than 60 hours to be fully restored.

“Possibly Aguirre’s breaker did not switch; something similar to what happened on September 21, 2016,” Jaramillo wrote. “But the reality is the [plants], our generation, went offline for a failure we still cannot yet specify. When going offline due to a fault, the units that remain in service, two large units, Aguirre and Costa Sur, go offline, which are the largest units in the system. When these units leave the system, a deficiency of between 900 and 1,200 megawatts is created, and what do the other units that cannot supply the energy do? Well, they protect themselves with an isolated system,” Figueroa Jaramillo said.

“I know it creates unease in the country but we as an island are an isolated system,” he added. “What this system did was, that to avoid further major failures, it protected itself. And that is part of the qualities our system has.”

He pointed out that restoring service could take up to 36 hours because “when you have the whole system turned off, you have to start it up little by little. You have to first give it, as we say, juice to the Aguirre and Costa Sur plants because you have to turn on the pumping systems.”

The cause of the massive blackout was being investigated. Last Thursday, a fallen tree in the municipality of Cayey and a powerline fault were blamed for an outage that, at one point, affected about 900,000 customers in several towns. Prepa announced that service was restored 11 hours later.

Prepa had recently announced that power service had been restored to 97% of its about 1.5 million customers since Hurricane Maria destroyed some two-thirds of the island’s power distribution nearly seven months ago. Some 40,000 remain without service since September.