UPDATE 1-NRC to inspect San Onofre nuclear safety system

(Adds SCE comment, emphasizes issue and inspection timing coincidental to Tuesday's earthquake.)

LOS ANGELES, July 30 (Reuters) - The U.S. Nuclear Regulatory Commission is conducting a special inspection of the San Onofre Nuclear Generating Station in California that was planned before an earthquake shook Southern California on Tuesday, NRC and company officials said.

The Southern California Edison-operated plant continued operations Tuesday and Wednesday without interruption and reported no damage at the closest nuclear plant to the epicenter of a moderate earthquake centered east of Los Angeles. The plant is between Los Angeles and San Diego, in San Diego County.

So Cal Ed is a subsidiary of Edison International of Rosemead, California (EIX.N).

So Cal Ed officials emphasized on Wednesday that while the inspection was announced by the NRC on Wednesday, its timing the day after the earthquake is coincidental.

Gil Alexander of So Cal Ed said SONGS workers several months ago "discovered bolts connecting a battery to other electrical components were not as tight as they should have been" and reported the issue to the NRC.

NRC inspectors have noticed similar problems at SONGS since 2005 have affected the operation of an emergency backup generator and batteries used to supply power during accidents, the NRC said.

"We are concerned about the number of failures and want to take a look at the way the licensee has responded to the issue," said Region IV Administrator Elmo E. Collins.

A team of three NRC specialists will begin the inspection August 4. The team will write a report about a month after the inspection.

So Cal Ed operates SONGS and owns 78.21 percent of San Onofre's power output. The plant is also owned by Sempra Energy's (SRE.N) San Diego Gas & Electric subsidiary (20 percent) and the the city of Riverside, California (1.79 percent). (Reporting by Bernie Woodall; Editing by Christian Wiessner)