Con Edison’s move to cut off 30,000 customers off in southeast Brooklyn Sunday came with little warning — a last-second decision to prevent a larger crisis amid the weekend heat wave, utility officials said.

The shutdown was necessary to protect utility equipment and make it easier for engineers to restore service, according to Con Ed.

“That damage would have resulted in longer outages and potentially more customers losing service,” Con Ed said in a statement.

But Brooklyn residents affected by the outage, Mayor Bill de Blasio and Gov. Andrew Cuomo fumed they were given scant notice before the power was suddenly turned off.

“I can’t trust [Con Ed] at this point because I’m not getting any real answers,” the mayor told reporters Monday.

Cuomo also slammed the utility and again threatened to yank its operating franchise.

“This is a franchise that is not granted by God — it’s granted by the people of the city, and you can change a utility company if they don’t perform,” he said on WAMC-FM.

Weekend Record Power Usage

Con Ed officials say they were left with no choice and that service would have gone down for the residents in Brooklyn even without the pre-emptive action.

Demand fueled by boiling residents blasting their air conditioners hit a weekend record of 12,063 megawatts at 6 p.m., according to Con Ed.

About an hour earlier, overheated wires triggered a manhole fire in the area, said Con Ed spokesperson Alfonso Quiroz.

The shutdown came amid particularly high usage in Canarsie, Flatlands, Mill Basin, Old Mill Basin, Bergen Beach and Georgetown.

There were more than 13,600 customers still in the dark as of Monday evening — with 10,143 in the aforementioned sections of Brooklyn and 2,400 in Jamaica and Flushing, Queens. Power is expected to be fully restored by Tuesday morning.

City Councilmember Alan Maisel, who lives in Marine Park, lost power along with many of his constituents around 6 p.m. Sunday.

“I didn’t sleep a wink last night because it was too hot,” he said, noting his power was restored around 5 p.m. Monday.

Con Ed reduced voltage by 8% shortly before cutting service.

‘Caught Flat-Footed’

But Maisel, and others in the area, were frustrated there wasn’t more notice.

“A lot of people were caught flat-footed,” he said. “They didn’t realize this was a possibility.”

Con Ed issued a press release about 45 minutes before the blackout urging residents in the area to conserve energy.

Some residents never got the warning.

“I got home from work at 12 a.m. [and] I was like, ‘Damn, what happened?’ ” said Anton Thomas, 20, a mechanic who lives on East 57th Street near Ave. K in Flatlands.

“I was working on a hot day,” he added. “I wanted that A/C bad. I had an uncomfortable sleep.”

Andre Marcellus, who lives in Canarsie, initially thought he dodged the blackout.

“My friend heard first and called me,” he recalled. “She was like, ‘Did you lose power?’ I said no. Then 30 minutes later, I lost it.”

Con Ed officials said they do everything possible to avoid shutting of service, and noted that the utility has a staffer embedded in the city’s Office of Emergency Management headquarters.

It marked the second blackout this summer, following the large July 13 outage in Manhattan. The state’s Public Service Commission is probing that incident, which utility officials have blamed on busted 13,000-volt cable.

Maisel said he was looking forward to a City Council hearing on the summer outages.

“It would be nice to have them give a public explanation,” Maisel said, noting he would rely on industry experts to determine what happened.

“In order to find out the truth we need people who know the business to determine whether they took prudent actions,” he said. “To catch a thief, you need a thief.”

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