ONTARIO, N.Y. (AP) Federal authorities say a generator fault caused a western New York nuclear plant to automatically shut down as a safety precaution.

A Nuclear Regulatory Commission spokesman tells the Rochester Democrat and Chronicle (http://on.rocne.ws/145nIsR ) that the Ginna (guh-NAY') plant's reactor was stopped by control rods just before 2:30 p.m. Wednesday.

He says investigators are trying to determine why the generator went off-line during a test.

The shutdown happened as plant workers and emergency crews were engaged in a safety drill.

The 43-year-old plant is owned by Baltimore-based Constellation Energy Nuclear Group.

It isn't known when the reactor will be restarted.