On average, U.S. electricity customers experienced just over seven hours of electric power interruptions in 2021, almost an hour less than in 2020. When major events—including snowstorms, hurricanes, and wildfires—are excluded, the average duration of interruptions annually remained consistently at around two hours per year from 2013 to 2021.

A number of factors cause power interruptions, including weather, interference from vegetation near power lines, and utility practices.

One metric used to measure the reliability of U.S. electric utilities is the System Average Interruption Duration Index (SAIDI), which measures the total time, on average, that a customer experiences non-momentary power interruptions in a one-year period. SAIDI is often paired with the System Average Interruption Frequency Index (SAIFI), which measures the frequency of interruptions.

Electricity customers in the District of Columbia, Delaware, Florida, North Dakota, and Nevada had the shortest total time of electricity interruptions in 2021, ranging from 52 minutes in the District of Columbia to 102 minutes in Nevada.

Customers in Louisiana, Oregon, Texas, Mississippi, and West Virginia experienced the most time with interrupted power in 2021, ranging from almost 19 hours in West Virginia to over 80 hours in Louisiana. Louisiana also had the highest number of power interruptions, followed by Texas. Long interruptions were largely because of extreme weather events. The United States experienced 21 named storms in 2021, the third-most active Atlantic weather season on record. In addition to four major hurricanes in 2021, a winter storm affected the central United States with Arctic air as far south as Texas.

In February 2021, winter storm Uri hit Texas, where about 4.5 million customers lost power, along with almost half a million customers in Louisiana and Oklahoma. The storm moved into the mid-Atlantic region, knocking out power in West Virginia and Kentucky. Both West Virginia and Kentucky are heavily forested, so power interruptions resulting from falling tree branches are common, especially as a result of winter ice and snowstorms that weigh down tree limbs and power lines. Oregon had both extreme heat and cold weather events in 2021, including a historic ice storm in February and the Bootleg wildfire in August.

In late August 2021, Hurricane Ida left 1.2 million customers in Louisiana without power, some for over two weeks, and it left almost 150,000 customers without power in Mississippi. Hurricane Nicholas followed about two weeks later, leaving half a million customers without power in Texas as well as parts of Mississippi and Louisiana.