According to
http://my.earthlink.net/article/top?guid=20130208/7f691ac0-78a7-483e-b050-eb6062ef98f6 Super Bowl blackout traced to preventive equipment
"An electrical device that had been installed expressly to prevent a power outage caused the Super Bowl blackout, ... Officials of Entergy New Orleans, a subsidiary of New Orleans-based Entergy Corp., said the device, called a relay, had been installed in switching gear to protect the Superdome from a cable failure between the company's incoming power line and lines that run into the stadium....
The switching gear is housed in a building known as "the vault" near the stadium that receives a line directly from a nearby Entergy power substation. Once the line reaches the vault, it splits into two cables that go into the Superdome.... It remains unclear whether the problem with the relay was a design flaw or a manufacturing problem.... "It's not unusual for them to have problems," he said. "They can be unpredictable despite national testing standards recommended by manufacturers."
