SAN JUAN, Puerto Rico (AP) — A private company says power has been fully restored to Puerto Rico’s 1.5 million customers nearly five days after a fire at a main power plant sparked an island-wide power outage.

Officials said Monday that they are now focused on investigating what exactly caused the failure of a circuit breaker at a substation within the Costa Sur power plant in southern Puerto Rico, one of four main plants in the U.S. territory.

The blackout that hit late Wednesday outraged and worried many, including those who cannot afford generators and have medical conditions including diabetes and respiratory issues that depend on electricity for their treatments.