The coroner identified the worker as 38-year-old Jose Raul Ros of Winchester. He was a distribution lineman.
The accident happened in the area of Ridgemoor and Murrieta roads just before 8 a.m. Ros was doing maintenance work in an underground vault, a facility that powers a nearby desalination plant. Authorities say three other workers were taken to local hospitals for smoke inhalation.
Southern California Edison says there are 12,000 volt transmission lines that feed the vault. But they still don't know exactly what happened that caused the explosion that killed Ros.
Southern California Edison says it does not appear that the accident had anything to with a copper theft incident Wednesday that knocked out power to 22,000 customers in the area.
Resident Dave Arnold says the explosion happened right behind his house.
"The boom sounded like maybe somebody was in an accident, or somebody ran into something, that was my first thought," he said. "It's sad, these are utility workers, and they have a job to do, but if it's a malfunction, or human error, you just don't know."
Spokesperson Raymond Hicks says the company's thoughts are with Ros' family.
"Our prayers and best wishes are with them, and the coworkers that are impacted by this," he said.
Ros leaves behind a wife and two young daughters. He worked for the company for 11 years, according to a company statement.
Southern California Edison is investigating the accident.