UPDATE 1-US FERC opens probe into Florida power blackout

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WASHINGTON, March 19 (Reuters) - The Federal Energy Regulatory Commission (FERC) on Wednesday said it has launched a formal probe into the power blackout that hit Florida on Feb. 26.

FERC said it was initiating a nonpublic, formal investigation into whether mandatory federal reliability standards were violated in the event, which affected about 1 million customers of four utilities across the state.

FPL Group's (FPL.N: Quote, Profile, Research, Stock Buzz) Florida utility Florida Power & Light said it would cooperate with the FERC probe, and its own preliminary investigation found that human error was a "primary factor" in the event.

The blackout affected about 584,000 FPL customers in South Florida.

Florida's grid operator and the the North American Electric Reliability Corp (NERC) -- the U.S. power grid watchdog group -- are also investigating the event.

FPL's blackout was the largest to fall under tough, mandatory reliability standards and penalties put in place after the August 2003 Northeast blackout, which left 50 million people without power.

Under the new rules, FERC can levy civil penalties up to $1 million a day for violations.

"The Florida blackout was a significant event that affected millions of Florida residents," FERC Chairman Joseph Kelliher said. "We must now determine whether the Florida blackout was related to violations of the standards and to apply any lessons we learn to improve the system."