As the city prepares for a final day of a record-breaking heat wave, Mayor Bloomberg is pleading with New Yorkers to conserve electricity at home and warning that the power grid may not hold if they do not.

Triple-digit temperatures led to new highs in energy demand for a second straight day, and while the mayor said major private entities have cooperated in the administration’s conservation push, he stressed that city residents need to do more.

With at least one more day of stifling heat ahead, the potential for a city full of residents returning home from work, switching the air conditioner to full blast, and turning on cooking appliances and televisions represented the greatest risk to the city’s fragile electrical grid.

“If we want to keep the power going, we’re all just going to have to conserve,” Mr. Bloomberg said at a news briefing at the city’s emergency operations center in Brooklyn. “I’ve done it in my house. I cannot stress it enough: Do it in yours.”

Yet the temptation to run — okay, walk slowly so as not to become drenched in sweat — for the air conditioning was never stronger than yesterday. Temperatures soared even higher than Tuesday, reaching 97 degrees Fahrenheit at Central Park and a record 102 degrees at La Guardia Airport, according to the National Weather Service. The heat index — what it actually feels like outside — topped out at 108 degrees at La Guardia.

Today should bring no reprieve. The forecast calls for temperatures to hover around 100 degrees again, with the possibility of strong thunderstorms late in the day. The mercury should dip to around 90 degrees on Friday, but the humidity is expected to remain until the weekend.

Consolidated Edison reported that demand for energy peaked at a record 13,141 megawatts at 5 p.m., up from yesterday’s mark of 13,103.

The strain of a second consecutive day of extreme heat led to more scattered power outages and brownouts throughout the city. Con Edison said last night that more than 2,000 customers in the five boroughs were without power, with the most in Queens and the Bronx.

The affected areas included northwest Queens, where thousands of businesses and residents have yet to recover from a 10-day blackout last month. Officials had warned that the damage suffered during the last heat wave had left that network particularly vulnerable this week.

At least one section of Woodside, Queens, lost power for nearly the entire day yesterday, beginning late Tuesday night.

For some businesses, the day was a painful return to the lost revenue and spoiled goods that marked last month’s outages. “Everything is garbage again, and so we’re back to square one,” the owner of Woodside Irish Deli on 61st Street, Leanne Bradley, said.

City officials said the Police Department had dispatched crews yesterday to help Con Edison determine the extent of power loss across the city.

The heat yesterday wreaked havoc in many ways. At a ceremony celebrating the expansion of the Museum of the City of New York, officials had planned an outdoor “groundbreaking” in which Mr. Bloomberg and other dignitaries would cut a cake designed as a replica of the renovated museum. Yet the meticulously detailed piece of edible art began to melt as soon as it was brought outside, looking more like a demolition than an expansion.

A raw egg cracked onto a newspaper vending box in Manhattan yesterday afternoon didn’t exactly fry, but seemed to bake and congeal. It was not eaten.

As New Yorkers endured the sizzling temperatures, the question was whether they would heed the mayor’s call for conservation by raising the thermostat to 78 degrees and turning the air conditioner off when they left home.

“I just wouldn’t do it,” Julie Goldin of the Upper East Side said. “I turn it down during the day when I’m not home. But I’m definitely going to need it.”

Daniel Nieto of Corona, Queens, said he would use a fan at home. “We’ll try to save some energy,” he said.”I will try to help a little bit.”

The city continued its own energy reduction measures, putting more facilities on backup generators, turning off the lights on bridges and many city landmarks, and dimming lights and raising the thermostat at municipal buildings. While emergency medical calls rose about 20% from this time last year, no heat-related deaths were reported.

Also yesterday, the Con Edison chairman, Kevin Burke, delivered a 107-page report to Mayor Bloomberg detailing the outages that hit northwest Queens last month, and what the utility did in response. The initial report does not reveal the cause of the outages, which Mr. Burke said would not be known for months.

“Am I satisfied with it? Of course not,” Mr. Bloomberg said, adding that the city would seek more definitive answers from Con Edison and had hired an outside legal counsel specializing in energy, Couch, White, to aid in an investigation being conducted by the state’s Public Service Commission.