San Diego State University Professor Murray Jennex works as a consultant with the nuclear power industry. He worked at the San Onofre Nuclear Generating Station for 20 years.
Jennex said the source of San Diego County's electrical power comes from three sources: Eastern and northern transmission lines and local generation.
He said at least two of those sources are needed to keep the juice flowing.
Jennex had this explanation for what happened when the Arizona electrical utility worker removed a piece of monitoring equipment at the power substation in Yuma:
"This operator in Arizona managed to cause his line to disrupt and when it dropped or failed, it caused a low voltage situation in San Diego," said Jennex. "Low voltage went across the county over the network and affected the San Onofre Nuclear Generating Station on the northern transmission side and caused San Onofre to trip off line or fail and that's when we lost two sources of energy and that meant that the third one just couldn't handle the load and the system collapsed."
But how could one person cause an entire electrical transmission system serving millions of people in several states and Mexico to fail?
"How he did it I'm not sure," said Jennex. "The San Onofre Nuclear Generating Station reacted the way it was supposed to undervoltage it has to protect the nuclear reactor and keep the equipment from being damaged. So it did what it was supposed to from being damaged. But my concern is that the network between the eastern transmission substation and the northern transmission substation somewhere in that network should have reacted and isolated and prevented that undervoltage from transmitting across the county."
He also said it is likely the control systems now in place are not fast enough to catch problems like the one which caused Thursday's blackout.
He said the system is designed to protect itself, but it failed.
Meanwhile, the Arizona utility has launched an investigation into the massive blackout which affected millions of people in southwest Arizona, southern California and parts of Mexico. The focus is on failed safeguards a substation in Yuma.
The North Gila substation is located northeast of Yuma. It is a 500,000 volt facility which converts energy to levels suitable for transmission lines between California and Arizona.
A worker there was removing a capacitor in the substation that regulates volt levels. Arizona Public Service Company said something happened to take the 500,000 volt transmission line out of service.
Utility spokesman Damon Gross said that's not supposed to happen.
"If that incident happens and that transmission line goes off line, there should be no impact to any of our customers whatsoever," said Gross. "And that is going to be a key component of our investigation moving forward. So there's really two parts of it: one is the human component, but I think more importantly is why wasn't the issue isolated and why did it spread."
Gross said APS is working with the California Electric utilities and others to find out why the blackout spread so far.
Michelle Faust in Yuma, Arizona contributed to this report for the Fronteras Desk.
