BANGOR – Hot and humid weather caused three power generators in New England to trip off line Monday night, significantly reducing the amount of electricity available for consumption Tuesday and forcing the overseers of the power grid to make calls for conservation.

The torrid temperatures also sent several people to hospitals complaining of respiratory problems and other heat-related symptoms.

New England set a record for power usage at 3 p.m. Tuesday, consuming 23,655 megawatts of electricity. The previous record was set July 6, 1999, when 22,544 megawatts was used. On that day, the region was under its third power warning of the summer.

“The power plants that tripped off line created a tight capacity, tighter than we’d like to see,” said Ellen Foley, spokeswoman for ISO New England, the governing board of the six-state power grid.

The names of the power generators could not be disclosed because of confidentiality agreements, Foley said.

Calling a power watch, or even a warning, was something ISO New England was not expecting to do this summer. Earlier this year, ISO announced that it did not anticipate a power crunch this summer because of at least 5,000 megawatts of new electricity available for use from newly constructed generators.

Under a power watch, electricity users are asked to voluntarily conserve energy by turning off unnecessary appliances and business equipment, and turning up air-conditioner thermostats.

If a power watch does not reduce the strain on the grid, a power warning is issued. Under a warning, urgent appeals for conservation are aired, including a request for high-volume users to interrupt production until demand slackens and a suggestion to state governors that they send workers home for the day.

Mainers typically use less electricity than what is generated within the state’s borders, said Phil Lindley, a spokesman for the Maine Public Utilities Commission. Starting Monday, the PUC was informed by ISO that the tie line that connects Maine’s transmission systems to the rest of New England was at capacity, he said.

New England was 200 megawatts shy of the amount of electricity it needed for consumption and reserve Tuesday, Foley said. More than 600 megawatts of power were purchased from New Brunswick, and 200 megawatts were sent from New York.

Being asked to conserve energy was not the only thing that people were asked to do Tuesday. With ozone reaching unhealthful levels, people were warned to limit their outdoor activities. Even with precautions taken, numerous people went to area hospitals complaining of respiratory problems and other heat-related symptoms.

“We’ve seen a few cases,” said Bethany McKnight, spokeswoman for St. Joseph Hospital in Bangor. “The [emergency room] expected to see more people than they have because of the heat. People are taking precautions, and that’s good.”

At Eastern Maine Medical Center in Bangor, one person was being evaluated Tuesday afternoon for heat stroke and several others complained of respiratory problems, said spokeswoman Elizabeth Sutherland. No cardiac arrests or deaths because of heat were reported.

“This is a typical average day for a hot day in the summer,” said an EMMC emergency room nursing supervisor.

At Maine Coast Memorial Hospital in Ellsworth, patients were treated for heat-related discomforts, but no cases of heat stroke were admitted, said spokesman Don Baril.

Temperatures did not top records, but it did reach 93 degrees in Bangor, three degrees shy of the top mark set in 1941, said meteorologist Michael Fitzsimmons of the National Weather Service in Caribou.

A cold front moved through the state Tuesday night, bringing thunderstorms to areas of the state. What the front is taking with it is the humidity, Fitzsimmons said. Temperatures today will be in the mid-70s in northern Maine, high 70s along the coast, and in the low 80s in the Bangor area, he forecast.

“The big difference you’ll see [today] is the humidity,” Fitzsimmons said. “It will be a lot less. A very refreshing air mass will be coming in after this cold front goes away. It will be comfortable [today].”

Amanda Dumond of the NEWS Staff contributed to this report.