A government task force says there were voltage shifts, line problems and power plant shutdowns in several states in the hours before the nation’s largest blackout. A time line released Friday by a U.S./Canadian task force doesn’t provide and new indication on what precisely triggered the August 14th blackout that investigators believe started with power line problems in Ohio. The task force says most of the events that appear to have contributed to the blackout occurred in the afternoon before the blackout. But there were events that occurred before noon that also may be relevant. The group says more work needs to be done before a cause of the outage can be determined and why it spread to widely and quickly.