The 2017 Puerto Rico Hurricane Maria Blackout

Hurricane Maria made landfall in Puerto Rico on 20 September 2017 as a Category 4 storm with sustained winds above 155 miles per hour. Two weeks earlier Hurricane Irma had already left 70% of electricity customers without power. After Maria, the island's emergency management office reported that the central power system was incapacitated and the whole island was without electricity.

The grid was already in poor condition, which the Congressional Research Service put down largely to underinvestment and deficient maintenance at the Puerto Rico Electric Power Authority (PREPA), the island's largest electricity supplier. Officials first estimated that many of the island's 3.5 million people could be without power for up to six months. Federal agencies brought about 900 portable generators and assigned the US Army Corps of Engineers to oversee repair of the transmission system, while PREPA focused on distribution lines and service connections.

When the Corps' grid repair mission ended on 18 May 2018, almost 99% of PREPA's customers had service again, but more than 16,000 customers, mostly in rural areas, were still without electricity after eight months. The Corps described the restoration as incomplete, much of it a patch up, and attention turned to rebuilding a grid that could withstand extreme weather.