Investigators say three failed transmission lines in Ohio likely caused this week’s blackout. Experts are working to understand why the disruption spread throughout the Northeast and Midwest and into Canada, and was not contained. North American Electric Reliability Council Chief Michehl Gent says the council is fairly certain that the problem started in Ohio. Gent says the transmission system was designed to isolate problems such as those apparently involving the three lines in the Cleveland area. He says the disruption should have stopped after the first three line failures.