Residents of Arizona, Southern California and Mexico woke up with their lights back on this morning after a major power outage sparked by a single utility company worker left millions of them in the dark overnight.
Officials with San Diego Gas & Electric Co. confirmed that, as of around 4:30 a.m. PST, all power had been restored to the area's 1.4 million customers. Power was restored late Thursday to millions of consumers in Arizona and parts of California's Orange and Imperial counties also affected by what officials described as a "cascading" blackout, and the worst in California history.
The massive blackout, which shut schools, grounded planes and brought business and traffic to a halt, was caused by one utility worker performing routine maintenance at a power substation near Yuma, Ariz.
The result, from the deserts of Arizona, was a 12-hour, full system blackout for 5 million people across San Diego County, southern Orange County, western Arizona, northern Baja California and even into areas of Mexico.
The problem began just before 3:30 p.m. Thursday when a worker for Arizona Public Service, the state's largest utility provider, replaced monitoring equipment that had been causing problems, creating a short-term power outage for about 56,000 customers in Yuma and western Arizona.
Ten minutes later, an attempt by workers at the same substation to restore power was unsuccessful and, instead, shortened the circuits.
Because the substation is a main point of delivery between power plants in Arizona and San Diego, the electric system shut down across the Southwest in what officials with San Diego Gas & Electric described as a "cascading effect."
The blackout extended south of the border to Tijuana, Mexicali and other cities in Mexico's Baja California state, which are connected to the U.S. power grid and have a combined population of 2.5 million people who were affected.
Typically, in such an instance, the outage would be isolated to the Yuma area. The investigation is now focusing on the reason that did not occur in this case, APS said Thursday.
The loss of power led to a shutdown of two reactors at the San Onofre nuclear power plant. Officials from the U.S. Nuclear Regulatory Agency said it appeared to have shut down automatically at 3:38 p.m. because of the change in the power grid -- as it is designed to do, kind of like a circuit breaker. Officials worked overnight to reconnect the reactor so that it could help restore power to some of the many people affected.
There are safeguards built into electrical systems across the country," said Stephanie Donovan, a spokeswoman for SDG&E. "When the power plant shut off at San Onofre, it was a built-in, automatic protective device. ... The reason that the outage tends to cascade is that the system tried to protect itself from voltage fluctuations."