A relatively minor glitch in Florida's electrical grid somehow triggered a chain reaction on Tuesday that caused a nuclear plant to shut down and briefly cut power in patches around the state.

Up to three million people, about a fifth of Florida's population, lost power at various points during the afternoon, though there were no safety concerns at the nuclear plant.

While many areas were hit hard, the outages were short lived and only about 20-thousand people lacked electricity during the evening commute home. Most of the evening outages were due to bad weather, not the grid problem, officials said.

The utility was trying to determine what caused equipment failure and a fire at the substation, but the company said it was not the kind of problem that should have created the widespread blackouts.

Grid problems caused both Turkey Point reactors to shut down, but the power station was more than prepared to handle the glitch he said.

The acting Deputy Regional administrator of the Nuclear Regulatory Commission, Charles Casto, said the losses of power were ''not unusual.'' ''The plant responded as desired,'' he added.

The outages had no connection to terrorism, Homeland Security Department spokeswoman said. Miami-Dade County Mayor Carlos Alvarez said the outages were technical, not criminal.

Florida emergency management officials said the outages cut power to 2 to 3 million people during the heat of a day that saw temperatures reach the 80s.

The federal nuclear commission said based on reports from its resident inspectors at the plant, the initial drop in voltage came from outside Turkey Point, but the problem worsened when the two reactors shut down, the panel said.

The Federal Energy Regulatory Commission, which has responsibility for electricity grid reliability, said it wants to know whether there were any violations of federal grid reliability rules.

The sporadic outages spanned 300 miles of the peninsula but appeared to be concentrated in the southeast portion of the state, including Miami. Communities along the southwest coast, in the Florida Keys and as far north as Daytona Beach reported interruptions.

Miami International Airport, the Port of Miami and the area's rail and bus transportation were working normally, although some places briefly relied on generator power.

By afternoon, most of northern downtown Miami appeared to be back to normal operation, including a campus of Miami Dade College and numerous stores and businesses. In the Florida Keys, a spokesman said areas were without power for about 30 minutes.

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