SAN FRANCISCO (REUTERS) - A Silicon Valley power substation was damaged after rifle shots were fired at it early on Tuesday morning, leading the California grid operator to call for electricity conservation.

Electricity in the tech capital has not been interrupted so far, as residents and businesses have responded well to the call to save power, said Mr Steven Greenlee, a spokesman for the state grid manager.

Gunfire was heard about 1:46 a.m. (4.46am Singapore time) at the Metcalf substation on the southeast outskirts of San Jose, according to Kurtis Stenderup, a spokesman for the county sheriff. Investigators later determined a high-powered rifle had been used, and they are treating the damage as an act of vandalism, he said.

About a quarter of an hour before the shots, someone cut fiber optic cables belonging to AT&T, located about a half-mile from the power station and due to the close timing and proximity, investigators believe the incidents are linked, he added.

The Independent System Operator requested conservation in a"Flex Alert" for Northern California just before 10 a.m. Pacific time on Tuesday. The operator will announce late in the evening whether conservation will be necessary on Wednesday as well.

He did not know when the station, owned by PG&E Corp's Pacific Gas and Electric, might be back to normal but said that switching out transformers "takes a while."