McDonald estimated that Peco would be able to restore service to all but the last 50,000 customers by Friday morning, thanks to help from more than 700 workers from ComEd, Peco's sister utility in Illinois, and from power companies as far away as Florida, Louisiana, and Mississippi who have come to assist.
He said the last few thousand households could take until next Tuesday to restore, as crews focus on damage to wires, poles, or switches that affect only a handful of customers.
"It'll be the same amount of work, but you'll be putting on 10 customers here, two or three there," McDonald said. "But it still takes the same crew."
Power outages have a wide variety of causes that make predictions tricky, according to utility officials and outside experts.
"Each storm is different, just based on the root causes of the power outages," said Jennifer Kocher, spokeswoman for the Pennsylvania Public Utility Commission, which oversees the state's regulated utilities.
Hurricane Sandy, which interrupted power to more than four million customers as it devastated much of the Eastern Seaboard, is a perfect example.
In New Jersey, the same record-breaking storm surge that caused billions of dollars in property damage also challenged the region's utilities in unusual ways.
About 1.4 million customers of New Jersey's Public Service Electric & Gas Co., whose territory stretches from the Philadelphia area to the New York suburbs, lost power during Sandy. But about 500,000 of them were interrupted intentionally, when the utility faced flooding in a half-dozen major switching stations in North Jersey.
At a news conference Tuesday, PSE&G's top executives explained why they essentially had to flip switches that cut off power to entire cities such as Newark and Jersey City, as they faced the risk of flooding at facilities full of high-voltage equipment.
It wasn't for lack of preparation, said Ralph LaRossa, PSE&G president and chief operating officer. Like other utilities throughout the region, PSE&G had planned for days to cope with Hurricane Sandy's widely predicted onslaught.
LaRossa said the utility even installed sandbags to protect stations that had flooded from heavy rain during previous hurricanes. But the utility guessed wrong - rather than the rain, Sandy's storm surge proved to be its biggest punch. As the waters threatened the utility's equipment, PSE&G had to pull the plug on more than 50 large transmission lines, he said.
"This wall of water that's hit the state of New Jersey is not something we could have prepared for," LaRossa said.
South Jersey's other major power provider, Atlantic City Electric, was forced to take similar steps in Ocean County, Vince Maione, regional president for the utility's parent company, Pepco Holdings Inc., said at a news conference Tuesday.
Maione said Atlantic City Electric was advised to cut power to substations in the Ocean County area by officials at PJM Interconnection, the company that manages the region's electrical grid, when there were signs of a voltage surge.
"De-energizing is the most drastic thing we can do," Maione said. By Tuesday night, Atlantic City Electric said, about 163,000 customers still lacked power, down from a peak of about 217,000.
LaRossa said PSE&G expected it would take less than 48 hours to restore large numbers of customers affected by the decision to shut off transmission lines - essentially, the high-volume portion of the electric system. But he said it could take much longer to restore some customers. "Stragglers could be well past seven days," he said.
That has happened before to Peco customers, said spokeswoman Karen Muldoon Geus.
Geus said Peco took about 10 days to restore the last customer after the utility's previous record outage, caused by a 1994 winter storm utility workers nicknamed "Ice Breaker" that she said affected about 520,000 area customers.
Last year, Peco took seven days to restore power to about 511,000 customers who lost power during Hurricane Irene.
Contact Jeff Gelles at 215-854-2776 or firstname.lastname@example.org.
Staff writer Andrew Maykuth contributed to this article.