Shabab Mehraeen, an assistant professor of electrical engineering at Louisiana State University, said the relay device is a common electrical fixture in businesses and massive facilities such as the Superdome.
"They are designed to keep a problem they sense from becoming something bigger, like a fire or catastrophic event," said Mehraeen, who holds a doctorate from the Missouri University of Science and Technology in Rolla, Mo.
The devices vary in size, and while Mehraeen noted he was not familiar with the specifics of the relay at the Superdome, he added, "I wouldn't be surprised if it was bigger than a truck."
Mehraeen said the reasons the devices fail are the subject of much academic research into the interaction of relays with the complex electrical systems they regulate.
"It's not unusual for them to have problems," he said. "They can be unpredictable despite national testing standards recommended by manufacturers."
Entergy and SMG had both upgraded lines and equipment in the months leading up to the Super Bowl. Rice said the new switching gear, with the faulty relay, was installed as part of a $4.2 million upgrade by Entergy, including the installation of a new power line dedicated solely to the stadium.
In a separate project, SMG replaced lines coming into the stadium after managers expressed concerns the Superdome might be vulnerable to a power failure like the one that struck Candlestick Park during a 49ers Monday Night Football game in 2011. That outage was blamed at least partly on a transformer explosion.
Thornton stressed Friday that the dome was drawing only about two-thirds of its power capacity Super Bowl night, and said typical NFL games in late August or September can draw a little more.
City officials had worried that the Super Bowl outage might harm New Orleans' chances of getting another NFL championship game.
But NFL Commissioner Roger Goodell downplayed that possibility after the outage, saying the NFL planned to keep New Orleans in its Super Bowl plans. Mayor Mitch Landrieu said the city intends to bid for the Super Bowl in 2018.
Earlier Friday, Entergy said the device was the cause of the power outage.