Electricity use has surged to record levels as consumers try to stay cool in the midst of an oppressive heat wave.

Duquesne Light posted a new record for peak demand Wednesday between 4 and 5 p.m. It was the third time this summer that Duquesne Light had posted a record. The new record, 3,035 megawatts, was slightly higher than the record set Tuesday, 3,000 megawatts. The previous record, 2,887 megawatts, was set July 20.

At Allegheny Energy, peak demand on Wednesday topped out at 8,703 megawatts. The record, set July 26 of last year, was 8,824 megawatts, but the company has a smaller service area and fewer customers than it did last year. Spokesman David Neurohr said Wednesday's number was a record for the smaller company.

PJM Interconnection, which operates the electricity grid for 13 states, including Pennsylvania, said demand set a record Wednesday as well. Like Duquesne Light, PJM had two record-setting days in a row: The 144,796 megawatt peak on Wednesday followed a record demand of 144,000 megawatts on Tuesday.

PJM's first record-setting day of the summer was July 17, when usage peaked at 139,746 megawatts. One megawatt of electricity is enough to power 800 to 1,000 homes.

Mr. Neurohr said that even at record levels of usage, there's more than enough electricity to go around.

"If our customers' demand exceeded our ability to generate, which has never happened, we would just purchase it on the open market through PJM," he said. "But that's really not a very credible scenario."

However, the heat has resulted in sporadic outages as transformers have failed, overloaded by the demand. Duquesne Light spokesman Joseph Vallarian said some 150 transformers had been replaced this week, out of more than 100,000.

"We jumped into storm mode, because this is a storm of sorts," Mr. Vallarian said. "The difference is you don't have a high concentration of people in one area that are without power. It's smaller numbers, and it can usually be repaired fairly quickly."

He said on average, work crews have replaced failed transformers within an hour. Perhaps more importantly, the new transformers have 50 percent more capacity than the old ones, and thus should be better able to handle increased user demand.

Even so, both PJM and local utilities have encouraged consumers to conserve electricity by taking such steps as drawing the curtains on south-facing windows or operating dishwashers during off-peak hours.