California's grid operator is calling for people to limit their electricity usage amid a historic heat wave that is straining the power system in the U.S.' most populous state. The California Independent System Operator (CAISO), which oversees the state's power grid, on Tuesday afternoon issued an "emergency alert" asking residents to use less power between 4 p.m. and 9 p.m. "[R]eal-time analysis shows all resources are committed or forecasted to be in use, and energy deficiencies are expected," CAISO said in a bulletin. The grid operator expects power demand on Tuesday to rise to 52,000 megawatts, exceeding records set in...