The smoke created by the burn-off at refineries near the Port of Los Angeles also prompted officials to evacuate Los Angeles Harbor College, where students were sent home for the day. People living near the harbor were advised to stay inside and keep their doors and windows closed.
The outage began when workers installing an automated alert system cut several wires simultaneously, instead of one at a time, according to Ed Miller, of the Department of Water and Power.
The error prompted two generating stations and other receiving stations to shut down. That in turn forced the department to begin cutting power to people across the city to stabilize lines.
Though some power experts said the system performed correctly given the surge, it was the latest indication of the vulnerability of the nation's electrical grid.
In 2001, power shortages in the state caused rolling blackouts. And a blackout in August 2003 that started in Ohio cascaded across the East and into Canada, affecting 50 million people.
The latest outage spread north into the San Fernando Valley and hit neighboring cities, including Burbank and Glendale. But because of the region's patchwork utility system, pockets of power remained.
The electricity continued to flow in the seaside city of Santa Monica, for example, while the adjacent Venice Beach section of Los Angeles went dark.
There was confusion at major traffic intersections as motorists tried to nose their cars through darkened stoplights, jamming exit ramps and freeways.
Katie Cerio, a stylist for TV commercials, said traffic signals were out in her Los Angeles neighborhood but they were on in the nearby city of West Hollywood.
"They've got people directing traffic, but it's definitely a bit chaotic," Cerio said from her car.
At the Bob's Big Boy restaurant in Burbank, power was out for about 90 minutes. "All we could serve were salads and cold sandwiches, no hamburgers," manager Frank Rodriguez said.
