Feb. 29 (Bloomberg) -- FPL Group Inc., owner of Florida's largest electric utility, said human error was the primary factor responsible for blackouts in the state on Feb. 26.

A field engineer had been diagnosing a switch that malfunctioned at the Flagami substation in west Miami, the Juno Beach, Florida-based company said today in a statement. Without authorization, that person disabled two levels of relay protection, FPL said, and a fault occurred during the diagnostic process.

The resulting event affected 26 transmission lines and 38 substations, the company said. FPL said about 584,000 customer accounts were affected, or 13 percent of its total. Almost everyone's power was restored by 4:30 p.m. that day, FPL said. About 3 million people in the state lost electricity, the Florida Division of Emergency Management said earlier this week.

``While in this instance we failed to perform to our expected standards in regard to reliability, safety was never an issue and the safeguards built into our system worked as intended,'' Armando Olivera, president of the Florida Power & Light unit, said in the statement.

FPL said an affected substation serves three units at the Turkey Point plant, including one fueled by natural gas and two nuclear reactors that shut. Two other plants in FPL's system were affected, and the system lost 3,400 megawatts of generation capacity.

The engineer involved in the situation has been suspended with pay pending the investigation's outcome, Olivera said today on a conference call with reporters.

``It's an employee that has a significant tenure with the company,'' he said.

To contact the reporter on this story: Edward Klump in Houston at eklump@bloomberg.net.

Last Updated: February 29, 2008 17:53 EST