Monday's power emergency came after rotating outages were ordered in parts of the state Friday and Saturday evenings because of a dangerously low level of reserve power.
The power agency, PG&E, Gov. Gavin Newsom and others are cautioning that with the statewide heat wave expected to continue through at least Wednesday night, further blackouts will be avoided only if Californians continue efforts to conserve power.
The California ISO is forecasting record demand Tuesday.
Original post, last updated 6:30 p.m. Monday
Gov. Gavin Newsom called Monday for an investigation into why the agency that manages the state's power grid imposed two nights of rolling blackouts over the weekend.
Newsom's directive was accompanied by an emergency proclamation allowing some large energy users, including ships anchored in the state's ports, to use generator power instead of drawing electricity from the state's overstretched grid.
Even as the governor explained his directives during a noon media briefing, officials with the California Independent System Operator were saying in a separate public meeting that rotating power outages were likely in some parts of the state as early as 3 p.m. to 4 p.m. Monday.
The agency said in a media briefing early Monday afternoon that as many as 3.3 million utility customers statewide could be affected later in the day by rotating blackouts, with outages for individual customers lasting one to two hours.