Office workers wait for building elevators to resume working during a power cut in downtown San Francisco, California, U.S. April 21, 2017. REUTERS/Alexandria Sage

SAN FRANCISCO (Reuters) - Fewer that 3,000 customers remained without electricity in San Francisco on Friday after a fire in a utility substation earlier in the day knocked out power for much of the city, according to PG&E.

The fire, which left some 90,000 customers without power for hours, was caused by a failed circuit breaker, said PG&E spokesman Paul Doherty.