Around 7 p.m., Southern California Edison said at the direction of the California Independent System Operator, they were implementing rotating power outages.
According to SCE, the rotating outages typically last about an hour.
Just before 7:30 p.m., the City of Anaheim said rolling power outages were underway across the city and would last "no longer than 15 minutes."
"A Stage 3 Emergency is declared when demand outpaces available supply. Rotating power interruptions have been initiated to maintain stability of the electric grid," Cal ISO said in a news release.
Just before 10 p.m., the Stage 3 Emergency declaration had ended, according to Cal ISO.
The ISO has terminated its Stage 3 Emergency declaration. Power that had been disrupted as part of the emergency has been restored statewide. https://t.co/Khqz7UMv55— California ISO (@California_ISO) August 15, 2020
"It was triggered by not enough energy and we started to dip into our reserves, which is dangerous," said Anne Gonzales, a Cal ISO spokesperson.
A Stage 2 emergency was declared around 5 p.m. due to strain the state's power grid amid the scorching heat wave.
California #ISO has declared a statewide Stage 2 emergency, due to excessive heat driving up energy use. If system conditions don't improve, the ISO will call a Stage 3 with rotating power outages. https://t.co/19miIKaZDW— California ISO (@California_ISO) August 14, 2020
Cal ISO said the previously-issued Flex Alert was extended to 10 p.m., asking residents to conserve electricity.
Residents were urged to set their air conditioner thermostats to 78 degrees or higher, turn off unnecessary lights, and avoid using major appliances between 3 p.m. and 10 p.m. on Friday.
On Twitter, Cal-ISO warned "If system conditions don't improve, the ISO will call a Stage 3 with rotating power outages."
The Southern California heat wave is expected to last through the weekend.
The National Weather Service issued an Excessive Heat Warning for communities in Orange, Riverside and San Bernardino counties through Monday, in addition to a Heat Advisory for the Los Angeles coast and downtown.
Tips for staying safe during a heat wave as the temperature rises