The extreme heat is putting the United States' power grid to test as a major portion of eastern United States on Friday faced sweltering heat.

The National Weather Service issued excessive heat warnings and advisories for mid-Atlantic areas from Maine to Georgia. The heat wave that has broiled much of the eastern part of the nation this week concentrates on the East Coast Friday. The National Oceanic and Atmospheric Administration (NOAA) reported 132 million people in 29 states and Washington, D.C. are under heat advisories or excessive heat warnings for the day.

The combination of near-record heat and oppressive humidity produced heat index values of 115-120, and Washington D.C.'s heat index at 2 p.m.local time was 119. Heat index combines air temperature and relative humidity to determine how hot it feels in an area.

The heat put pressure on power companies. PJM, the nation's biggest power grid operator, said consumers used a record amount of power on Thursday and it expected near-record demand on Friday.

In Michigan, rolling power blackouts were put in place to help relieve stress on power plants, according to the Weather Service. It said 30,000 people were without power in Detroit.

In New York City, the heat prompted power provider Consolidated Edison to reduce voltage in some neighborhoods. The company said increased use of air conditioners could push power usage to a record on Friday.