COLUMBUS, OHIO ? Two Ohio companies at the center of the investigation into the nation’s worst blackout warned state regulators five months ago that their power systems could overload if the grid linking U.S. and Canadian utilities had problems.

FirstEnergy Corp. and American Electric Power said in long-term forecasts that they didn’t expect any of their own transmission lines or substations to fail this summer.

But both companies said that widespread outages were possible if the spaghetti-like system that links eastern states and Canada experienced unexpected changes in electricity flows, power transfers between regions, unexpected demands and extreme weather.

“Together, these factors … may lead to overload conditions,” FirstEnergy said.

Those are just the sorts of power grid disturbances that swept across eight states and the province of Ontario, Canada, on Aug. 14, spreading the outage to 50 million people.

Akron-based FirstEnergy is at the center of a U.S.-Canada inquiry of what caused the outage. The most prominent theory is that a FirstEnergy power plant in Eastlake, Ohio, and some of its electricity transmission lines failed, including one that sagged into a tree.

The resulting surge of power in Ohio spread, rocketing across transmission lines in Indiana, Michigan, Ontario and New York, and setting off automatic power shutdowns.

The two Ohio power companies say the Public Utilities Commission of Ohio has heard the same grid overload warnings from them for years and there is nothing that state regulators could have done with that information to prevent the blackout.

“It’s just a statement of reality. It’s a recognition of the fact that we are all interconnected and that there are strengths and weaknesses to that,” Ralph DiNicola, a FirstEnergy spokesman, said Monday.

“The good is that being interconnected enhances reliability. The not-so-good is that what happens on adjacent systems could impact our system,” DiNicola added.

Shana Gerber, a PUCO spokeswoman, said state regulators didn’t have the authority to help the utilities solve such reliability problems.

“All we can do is encourage these companies to participate in a regional transmission organization in which they can solve these issues internally,” she said.

In Indiana, James Torgerson, chief executive of the Midwest Independent Transmission System Operator, told state regulators Monday that the grid manager has increased monitoring of FirstEnergy, adding data collection points to watch voltage flows on its lines.

Torgerson also said the Midwest operator needed to improve communication among utilities, which now rely on old-fashioned telephone warnings to relay problems. On the day of the blackout, there was little or no warning for most U.S. utilities and Canada.

“It’s not very efficient when you have to start calling everybody,” Torgerson told the Indiana Utility Regulatory Commission.