SAN DIEGO — A blackout that swept across parts of the Southwest and Mexico apparently began with a single utility worker and a minor repair job.
How it then rippled from that worker in the Arizona desert to southern California and across the border, plunging millions of people into darkness on Thursday, has authorities and experts puzzled, especially since the power grid is built to withstand such mishaps.
"There are a lot of critical pieces of equipment on the system and we have less defense than we think," said Rich Sedano at the Regulatory Assistance Project, a utility industry think tank based in Montpelier, Vt.
The Arizona Public Service Co. worker was switching out a capacitor, which controls voltage levels, outside Yuma, Ariz., near the California border. Shortly after, a section of a major regional power line failed, eventually spreading trouble further down in California and later Mexico, officials said.
And the lights began to go out in a border region of roughly 6 million people.
The outage knocked out traffic lights, causing gridlock on the roads in the San Diego area. Two reactors at a nuclear power plant up the California coast went offline after losing electricity. More than 2 million gallons of sewage spilled into the water off San Diego, closing beaches in the nation's eighth-largest city.
A local think tank, the National University System Institute for Policy Research, estimates the outage cost the San Diego-area economy more than $100 million. Many people on both sides of the U.S.-Mexico border had to spend the night struggling to fall asleep in the heat.