A rolling blackout occurs when a power company turns off electricity to selected areas to save power. The areas are selected using sophisticated computer programs and models. The blackouts are typically for one hour, then the power is restored and another area is turned off. Hospitals, airport control towers, police stations, and fire departments are often exempt from these rolling blackouts. These blackouts usually occur during peak energy usage times, usually between 4 and 7 p.m. on weekdays, but they can happen at any time of day. Blackouts may affect the same area more than once a day, and may exceed an hour's duration.

Listen to local television, radio and check the web site of your local power company. Usually, rolling blackouts occur when power usage increases, especially during hot weather when many people are using air conditioning to keep cool. Power companies try to give a warning when they will turn off power to an area, but they cannot always do that.