The claim could not be confirmed late Sunday by independent sources. Engineers at another Midwestern utility reported no such unusual grid fluctuations, said an official at that company, who spoke only on condition of anonymity.
Officials at FirstEnergy Corp., the company whose power line problems have been cited as key in the blackout investigation, sought to go on the offensive Sunday, trying to deflect any potential blame for the cascade of power outages that struck Thursday from southern New England to Michigan.
"What happened ... is much more complex than a few tripped power lines in our system," FirstEnergy spokesman Todd Schneider said. He said that the utility's data showed unusual conditions, including strange fluctuations of voltage, in the Midwest grid "as early as noon" Thursday, more than three hours before the FirstEnergy lines failed.
The blackout hit its peak at 4:11 p.m. EDT.
Another FirstEnergy official, Ralph DiNicola, said, "We firmly believe it is an issue that goes beyond our lines." The company is the country's fourth-largest investor-owned utility, with 4.3 million customers in Ohio, Pennsylvania and New Jersey.
In a statement late Sunday, Michehl Gent, head of the North American Electric Reliability Council, an industry group investigating the power outage, acknowledged that the cause of the blackout has yet to be learned.
"Although we may have identified the area where the cascading outages began," Gent said, referring to the lines in Ohio that failed, "any attempt on our part to identify the cause of the outages at this point would be speculative and premature." He added that "events that occurred on one utility's system may have been affected by events on utility systems elsewhere" in the power grid.
The council also reported that as of Sunday evening all the electric transmission systems that had been affected by the blackout were again operating reliably, except for a link between Michigan and Ontario, Canada, which remains out "due to operational security reasons."
The statement did not elaborate, but it said the line was expected to return to service soon. Twenty-one power generating plants remained down, about a fifth of those that had been shut down by the blackout, the council said.
Federal investigators joined industry teams Sunday in the search for clues into what triggered the blackout.
Energy Secretary Spencer Abraham promised to move as quickly as possible to get answers and address whatever problem is found, but said so far there's no indication who might be responsible.
"We can't allow it to linger long. We need to address it," said Abraham, who made the rounds of the television talks shows Sunday and repeated a theme of confidence that the cause of the massive power disruption will be uncovered.
He too acknowledged the task of unraveling a cause will be difficult.
"It's going to take some time," Abraham said on NBC's "Meet the Press." He refused repeatedly during the day to speculate on the cause, whether it was human error or a mechanical glitch, or where the problem might have begun.
The industry investigation has focused on the likelihood of a combination of mechanical glitches and human failures as it tries to piece together second-by-second events during the hours before the widespread blackout, focusing on power lines in Ohio.
The council, which was created after another major blackout in 1965 to monitor the power grid and set voluntary reliability standards, has said the problem appeared to have cascaded after the breakdown in the three high-voltage lines south of Cleveland in the area served by utilities owned by FirstEnergy.
FirstEnergy acknowledged that an alarm that should have flashed a red warning on computer monitors when power was being lost, did not sound in its central control room.
That "certainly contributed to it," Gent said on ABC's "This Week." But he said the alarm did not fail at other locations where technicians were supposed to monitor the lines. "We have to dig into this to see why the alarm wasn't noticed by somebody else" in addition to why the alarm was not working at the FirstEnergy control center, he said.
On CNN's "Late Edition," Gent said that when the third line "tripped" — or lost power — "that should have separated the local system ... and the rest of the grid should have remained intact."