The utility said that workers from a "third-party construction company" caused the outage when they accidentally struck an underground line.
Embattled utility PG&E reported a service interruption on Friday that cut power to 22,000 customers - about 60,000 people - in San Francisco and stranded riders on the city's Muni rail service.
One reporter said problems with PG&E Substation A had likely caused the outage, which started just before 8 am PT. The utility is hoping to have power restored by 10:30. By 9:50 PT, power had been restored to some 7,000 customers, leaving 15,000 still without power.