A statewide Flex Alert, a request to voluntarily reduce power use by California’s power grid manager (ISO), is the first of several steps that Cal ISO might take to avoid power interruptions in the nation’s most populous state. The call for residents to voluntarily conserve power across California will be in effect during the Labor Day weekend heatwave. Cal ISO issued a Flex Alert starting Saturday and continuing through Monday for the hours of 3 p.m. through 9 p.m.