A massive power outage threw San Francisco into chaos for most of the workday on Friday, knocking out traffic signals, paralyzing businesses and halting the city's famed cable cars.
The power outage, which was triggered by a fire in a PG&E Corp. utility substation, disrupted San Francisco's financial district, home to banks and technology companies.
The blackout started just after 9 a.m. and at one point affected nearly 90,000 customers, according to PG&E. The cause of the fire was a circuit breaker failure at the substation, PG&E spokesman Paul Doherty said.