The probe into what triggered an eight-state, two-nation blackout (search) that left 50 million people in the dark zeroed in on an area just south of Cleveland, where a leading investigator said three transmission lines failed just before the massive outage.
With power finally restored, meanwhile, life was returning to normal in cities across the region Sunday, though there were lingering reminders: garbage cans overflowing with spoiled food, continuing water-boil warnings and the flood of questions asking how could it happen.
Michehl Gent, head of the North American Electric Reliability Council (search), suggested human error might have been the reason the problems were not isolated before they knocked out power from Michigan to Ontario to New York.
"The system has been designed and rules have been created to prevent this escalation and cascading. It should have stopped," Gent said in a telephone conference call.
Gent said investigators were examining more than 10,000 pages of data, including automatically generated logs on power flows over transmission lines, to determine what caused the blackout.
FirstEnergy Corp. (search), the Akron, Ohio-based utility that officials said owned at least two of the three lines, said alarm systems that might have alerted engineers to the failed lines were broken, but that functioning backup systems had been in place.
Nearly all of the millions affected by the blackout had power restored by Saturday, but people were still being urged to conserve electricity and many remained harried by aftereffects.
Thunderstorms Saturday knocked out power to a few thousand customers in the Detroit and Lansing areas. Crews worked into Sunday to restore service, and utility officials asked residents without power to call and alert them to isolated outages.
Water customers in parts of Michigan, Ohio and Ontario remained under warnings to boil water before drinking or cooking with it because water systems shut down by the outage were still being checked out.
Macomb County, Mich., ordered restaurants to shut down -- although that was news to Ali Harajli and the crowds gobbling up shish kabob and shawarma at his St. Clair Shores eatery.
"They have a point, and they have a right to do that," said Harajli, who had pots of boiling water ready for kitchen use. "Other restaurants in town probably don't take the same steps that we do."
In Manhattan's Midtown, hundreds wandered about Saturday on a sticky summer day at a street fair -- a typical, and welcome, scene after two days without power. All of New York City had power back by 9:03 p.m. Friday, and its subways were running a few hours later.
Turgay Agrali, a tourist from Turkey, stood in the crowd with a smile, comforted by the promise of air conditioning when he returned to his hotel.
"The first day I came was nice," he said. "The second day -- blackout."
There were still overflowing garbage cans scattered around Manhattan, but sanitation crews were working overtime through the weekend. Tons of trash had been piled on sidewalks as New Yorkers emptied their refrigerators of spoiled food.
The blackout occurred at 4:11 p.m. EDT Thursday, creating instant chaos.
New York Mayor Michael Bloomberg said Saturday that the outage disrupted the city's emergency ambulance and police radio dispatches for several minutes at a time. One of the failures caused a 14-minute gap in communications for dispatchers relaying calls to 911.
Ontario officials struggled Saturday to restore stable power throughout the province, but warned it could take days before everything is back to normal.
"It is not going to be an abundance of power on Monday morning," Ontario Premier Ernie Eves said. In Toronto, it was unclear whether subway service would be restored in time for the new work week on Monday.
In Michigan, DTE expected its plants to be at full capacity by Monday, even though the state's power system was especially damaged by the blackout. Because of its Great Lakes geography, the state has relatively few connections on the Lake Erie transmission loop with other states and Canada, so just before the blackout it received a huge surge of electricity that had nowhere to go.
"Power goes into Michigan or comes out, but it does not go through, for all practical purposes," said Gary Kitts, Michigan Public Service Commission chief administrative officer.
The energy situation remained tenuous in Michigan, where officials said it was critical for people to conserve electricity to avoid rolling blackouts.
Bettie Lloyd was undoubtedly among those most intent on avoiding a repeat. The auditor for the Detroit Board of Education was stuck alone in a hot, dark elevator for nearly 19 hours; firefighters finally freed her Friday after someone heeded her pleas for help.
"I prayed a lot," said Lloyd, 52. "I said, 'Oh my God, you're here! Thank you!'"