The power outage that hit Michigan was caused by a huge flow of electricity from southern Ohio through Indiana and Michigan that overloaded transmission lines in central Michigan, a transmission company executive said Wednesday.

The failure was tied to problems in northern Ohio, where the shutdown of several of FirstEnergy Corp. (search)'s generating plants and transmission lines in the hour before Thursday's blackout played a part in creating the electrical havoc that hit eight states and Canada, said Jack Welch of International Transmission Co. (search)

But the need to send FirstEnergy power from Michigan didn't cause Michigan's system to shut down, said Welch, president and CEO of the private transmission company based in Ann Arbor, Mich.

Instead, the separation of transmission systems in northern and southern Ohio from each other because of the problems in northern Ohio kept power from flowing from southern Ohio to FirstEnergy, Welch said.

Blocked from taking its normal route north through Ohio, the power instead flowed over American Electric Power (search)'s transmission system from southern Ohio through Indiana and into Michigan, then back to FirstEnergy's system in Ohio.

That suddenly put 4,800 megawatts of electricity onto Michigan's transmission grid, far more than the lines were able to carry, Welch said. The power grid began shutting down, leaving outages and dead generating plants in its wake.

"We're talking seconds here," Welch told the state Senate Technology and Energy Committee on Wednesday. "Those lines were never designed for that tremendous shot."

Welch said there was never a problem with handling the increase in demand from FirstEnergy's transmission grid, even when that demand went from 200 megawatts five minutes before the blackout to 2200 watts three minutes later.

"The system wasn't even feeling this," Welch said. "We didn't get dragged down. ... We had a voltage collapse."