PJM Interconnection LLC, the power grid operator in the Mid-Atlantic and Midwest, said Wednesday it reduced the electricity voltage in Maryland, Virginia and the District of Columbia to reduce the strain on the system.

New York's Consolidated Edison Inc. (ED.N: Quote, Profile, Research), meanwhile, said Wednesday it set another record for peak electricity demand of 12,792 megawatts at 2 p.m., beating the previous record of 12,551 MW set Tuesday.

One megawatt is roughly enough power for 800 homes.

Several utilities called on customers to conserve energy, and some implemented programs to compensate participants who curtail power usage, in an effort to prevent outages.

The heat is expected to break late Wednesday as a band of cooler weather marches across the region.

Meteorologists forecast temperatures in New York and Washington would climb into the upper 90s (Fahrenheit) on Wednesday with the humidity making it feel more like 110 degrees. The mercury on the western side of the cold front in Chicago and major cities in Ohio will stay below 80 degrees with no humidity.

A spokesman at PJM said the voltage reduction went into effect at 1:45 p.m. EDT for Constellation Energy Group Inc.'s (CEG.N: Quote, Profile, Research) BGE subsidiary, Dominion Resources Inc. (D.N: Quote, Profile, Research), Pepco Holdings Inc.'s (POM.N: Quote, Profile, Research) Pepco subsidiary and Allegheny Energy Inc.'s (AYE.N: Quote, Profile, Research) Allegheny Power service area in Maryland.

"We just want to do everything we can to maintain the safety margin," the PJM spokesman said.

The voltage reduction, which is not detectable by most electronic devices, reduces the amount of power used by reducing the amount of power flowing on the transmission lines.

In addition, PJM implemented its load response program in the east, which compensates customers with either lower cost power or payments to conserve energy when called upon by the grid operator.

The utilities that broke peak usage records this week include Exelon Corp.'s (EXC.N: Quote, Profile, Research) PECO subsidiary in Philadelphia, Southern Co. of Georgia, Pepco Holdings Inc. in Washington, Progress Energy's Progress Energy Carolinas subsidiary, SCANA in South Carolina, PPL Corp. in Pennsylvania, Consolidated Edison Inc. in New York and CMS Energy in Michigan.