The U.S. Energy Information Administration (EIA) reported that in 2018, electricity power outages on average were about 5.8 hours per customer.

Among almost 3,000 electric distribution systems in the United States, power interruptions vary in frequency and duration, caused by extreme weather, vegetation patterns and utility practices, among other things. The total time an average customer experiences a nonmomentary power interruption during a year, or the reliability of an electric utility, can be measured through the System Average Interruption Duration Index (SAIDI) metric.

For utilities that report SAIDI metrics using the Institute of Electrical and Electronics Engineers’ (IEEE) standards, nonmomentary interruptions are those lasting longer than five minutes.

The IEEE defines a power outage as a component’s inability to deliver power, whereas an interruption is the result of one or more of a component’s equipment outages. Utilities can report interruption durations including major events (such as extreme weather), without major events, or both.

Discounting major events or extreme weather, publicly owned U.S. utility customers experienced the least amount of service interruptions, averaging at only one hour of interrupted electricity service annually since 2013. Investor-owned utility (IOU) customers averaged slightly under two hours of interrupted service, followed by co-operative (co-op) customers, who averaged at roughly 2.5 hours.

Calculations that include major events show the same rank-order, with publicly owned customers experiencing slightly more than two hours of power interruptions in 2018. IOU customers had a little more than six hours of interrupted service, then co-op customers with about seven hours of interrupted service.

The EIA highlighted a few states in their reliability report for 2018. The range for power interruptions across the United Staes averaged only 1.5 hours in South Dakota, to slightly under 30 hours in North Carolina. Two years ago North Carolina experienced hurricanes Florence and Michael. Maine, Vermont, Massachusetts and West Virginia followed North Carolina in length of outages, mainly from falling tree branches from winter ice and snowstorms.

In 2017 and 2018, U.S. electricity customers experienced longer outages, mainly because of increases in interruptions with major events.

The EIA, which began collecting reliability data in 2013, said in 2017, the average outage duration with major events was twice as long as it was in previous years. Higher numbers of hurricanes, wildfires and severe storms across the United States were the main cause of the increase.