New Orleans — Entergy said Friday that it traced the cause of Sunday’s power outage at the Superdome to an electrical relay device that was designed to prevent such an event.

But what exactly caused that piece of equipment to fail, plunging half of the stadium into darkness for 34 minutes during the Super Bowl, remains unknown and something the utility’s executives and the device’s manufacturer said they continue to investigate.

Charles Rice, president and chief executive officer of Entergy New Orleans, told the City Council’s utility committee that a relay in the switch gear failed, causing the outage. The switch gear controls the flow of electricity from Entergy to the Dome.

“We are certain that this is the cause of the problem,” Rice told the five council members in attendance who regulate Entergy.

Rice said that the piece of equipment has been removed and replaced. Meanwhile, Entergy and the relay’s manufacturer, Chicago-based S&C Electric Co., are trying to determine why the device malfunctioned.

Rice pointed out that since Entergy completed $4.2 million in work to the switch gear and its home in a brick bunker outside of the Dome, the stadium has hosted several large events, including the Sugar Bowl, without any issues.

With Entergy taking the blame for the outage, a reverse in its position from Super Bowl night, Doug Thornton, the Superdome’s general manager, stressed that the building’s electric system is fine.

He said Saturday’s Endymion Extravaganza, hosted in the Dome, should not experience any problems.

“We have total confidence the Superdome’s systems are 100 percent intact,” Thornton said after Friday’s hearing.

While Entergy blamed the outage on faulty equipment, S&C, the manufacturer, said user error was the cause.

“In working with those involved, we found that the electric outage at the Super Bowl was a result of the electric load current exceeding the trip setting for the switch gear relay as set by the system operators,” S&C spokesman Mike Edmonds said in a prepared statement.” Based on the onsite testing, we have determined that if higher settings had been applied, the equipment would not have disconnected the power.”

Edmonds said S&C will continue to work with Entergy on the issue.

Entergy later Friday said testing that it and S&C conducted found that one relay functioned as expected while a second one did not functioned as expected.

“We’ll continue to do more tests,” Entergy Corp. spokesman Mike Burns said.

Before Entergy knew what caused the outage, the corporation said it would hire a third-party investigator to look into what caused the outage that stopped play between the San Francisco 49ers and Baltimore Ravens.

Rice was noncommittal when City Council Vice President Jackie Clarkson, who is not a utility committee member but attended Friday’s meeting, asked if that would still happen.

“We’ve told the public we’re going to have an outside investigation,” Clarkson said.

“We are certain this is the issue,” Rice replied.

“You were also certain it (the relay) would work, Charles,” Clarkson shot back.

Rice said that Entergy and SMG, the company that manages the Superdome for the state, would work together to determine if the outside review was necessary.

Asked after the meeting if he would press for the third-party review, Thornton said he would discuss the possibility with Entergy but ultimately would leave the decision to those officials.

“We don’t produce kilowatts,” he said. “We manage football stadiums.”

Shabab Mehraeen, an assistant professor of electrical engineering at LSU, 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 each did upgrades to their respective equipment in the lead up to the Super Bowl.

Rice said the new switch gear was part of the $4.2 million Entergy spent on upgrades. Thornton said the Superdome replaced feeder lines going into the stadium as a precautionary measure. Those lines, however, are not believed to have played a part in the outage and are separate from the switch gear.

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.

While there has been concern that the outage could harm New Orleans’ chances to land the Super Bowl in 2018, NFL Commissioner Roger Goodell has said the incident would not affect that possibility.

“We’d love to welcome back the NFL for our 300th birthday,” said Councilwoman Cynthia Hedge-Morrell, chairwoman of the utility committee, while noting that 2018 is the city’s tricentennial.

The Associated Press

contributed to this report.