Lonnie Charles Denison of South Natomas admitted Friday in U.S. District Court in Sacramento that he went into a room at the Independent System Operator's data center in nearby Folsom April 15, broke a glass cover and pushed the button for emergency power off, The San Francisco Chronicle reported Sunday.

Authorities said Denison, a contract employee at the data center, was upset with his employer.

Denison's move prevented the ISO from communicating to the electricity market for about two hours, leaving the electrical power grid vulnerable to shortages, Matthew St. Amant, a California Highway Patrol officer assigned to an FBI task force, wrote in an affidavit.

The incident cost $14,000 for 20 computer specialists to repair.

Denison was also charged with e-mailing a bomb threat the next day. Court records said the e-mail read: "Hey, at one point I respected you ... you have a new kid. So this is only because of him. Get out before the timer expires. Not long now. Take care."

Denison has pleaded guilty to felony attempted damage of an energy facility. He is scheduled to be sentenced Feb. 29.