Federal regulators will investigate the massive power outage that blacked out millions of customers in Southern California, Arizona and Mexico.
The Federal Energy Regulatory Commission said Friday that it will work with the North American Electric Reliability Corporation to determine what caused the blackout and how future problems can be prevented.
FERC spokeswoman Mary O'Driscoll says if regulatory violations are found, the commission could issue fines of up to $1 million per day for every violation.
The outage occurred Thursday afternoon after an electrical worker removed a piece of monitoring equipment at a power substation in southwest Arizona.
Authorities say the blackout wasn't deliberate. Power was restored by early Friday.
