BUENOS AIRES – Argentina has opened an inquiry into what caused a massive blackout that left nearly 50 million people without power, Energy Minister Gustavo Lopetegui said on Monday.

Technical data from the “black boxes” of two companies responsible for electricity supply will be examined in depth, and the results of the investigation would be published in 15 days, Lopetegui said on Argentine radio.

“Thousands of pieces of data” from the two companies, Cammesa and Transener, would have to be analyzed, he said. The government still does not know what caused the problem, more than 24 hours after the outage.

“The two companies have to provide the report of what happened over the next 72 hours, with that information Cammesa will provide a report of what happened until 7:07 am, and in 15 days we will know what was the sequence of events that caused the blackout,” Lopetegui told Radio La Red.

Electricity supply was cut off early Sunday to 44 million people in Argentina and 3.5 million in neighboring Uruguay. The blackout lasted more than 10 hours. Power was gradually restored through the day.

Mercosur members Paraguay, southern Brazil and Chile, also felt the effect of the incident.

The blackout halted metro and train services in Buenos Aires and forced hospitals and clinics in major cities to resort to using generators.

Investigations have so far focused on the electrical supply system from Yacyreta, a hydroelectric dam on the border with Paraguay.

The blackout “was something serious that should not have happened,” the minister said, adding that a key question was why normal safeguards did not kick in.

“We have to know why the system did not act as it does every day, because failures happen every day.” He added, “There is zero chance of a repetition”.

Argentina and Uruguay have a partially shared power grid centered on the bi-national Salto Grande dam, 450 kilometers north of Buenos Aires.–MercoPress