Photograph by Gerald Herbert, AP

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Fans and football players wait for Super Bowl action to resume in the partially darkened Mercedes-Benz Superdome on Sunday night in New Orleans. An electricity abnormality triggered the shutdown, but authorities are still investigating the root cause.

Photograph by Gerald Herbert, AP

What Caused the Super Bowl Blackout at the Superdome?

This Super Bowl’s post-game analysis will be like no other, as electricity and building systems experts probe the cause of the power outage that temporarily halted the Ravens-49ers game.

All that is known so far about the Mercedes-Benz Superdome power outage that temporarily halted last night's Super Bowl game is that a crucial piece of sensing equipment operated exactly as designed: It turned the electricity off.

But officials at the Superdome and its energy company, Entergy, said further investigation is needed to get at the root cause of the electricity abnormality that plunged half of the recently renovated stadium into darkness and forced a 34-minute delay of one of the world's most watched sporting events. (See related quiz: "What You Don't Know About Electricity.")

So while sports analysts dissect how the Baltimore Ravens held off the rallying San Francisco 49ers in the second half to secure their 34-31 victory, this year's postgame analysis will include scrutiny by teams of electrical engineers and stadium systems experts.

Despite much online speculation on the subject, it's unlikely that the scale of Beyoncé's dazzling, hologram-assisted halftime show was to blame for the outage, says James L. Kirtley Jr., professor of electrical engineering at the Massachusetts Institute of Technology.

It's possible, he said, that the cause was a simple overload, like what happens in a kitchen when a coffee pot and microwave are run at the same time. "The stadium system is, of course, a lot bigger, but fundamentally [it is] very similar" to a household circuit panel, Kirtley explained.

However, based on public statements from Entergy and the Superdome, Kirtley suspects that "some other piece of equipment failed and put a short circuit across the power circuit, causing a circuit breaker to open and disconnect power to some part of the stadium circuits."

After the stadium went dark, Entergy, which supplies electricity to 2.8 million utility customers throughout the Gulf Coast, quickly announced via its Twitter feed that its service to the stadium had not been interrupted. The problem, Entergy tweeted, was on "the customer's side." A later joint statement from Entergy and Superdome managers said the problems began when a piece of equipment designed to monitor electrical load "sensed an abnormality in the system."

"Once the issue was detected, the sensing equipment operated as designed and opened a breaker, causing power to be partially cut to the Superdome in order to isolate the issue," the statement said. "The fault-sensing equipment activated where the Superdome equipment intersects with Entergy's feed into the facility."

It is standard—in fact, usually required by law—for electrical systems to include circuit breakers that automatically shut off power to prevent wires from overheating and causing a fire. Circuit breakers can trip when there is too much load on a circuit, but a power outage also can be caused by a short circuit or other type of fault.

It's not known how much electricity the Superdome was drawing when the power outage occurred; Entergy said in response to a query that it was confidential "customer" information.

It is known that energy use from the Super Bowl was estimated in advance to be 4,600 megawatts, but that included the power for the NFL hotels and Morial Convention Center during the week of the game. Entergy had agreed in advance to donate carbon credits, or investments in carbon-capture projects, to offset the carbon emissions caused by that energy use—3.8 million pounds of carbon dioxide emissions—as part of a wide-ranging "greening" effort around the game. (See related photos: "Super Bowl Caps Banner Season in NFL Green Drive.") That's as much carbon as 359 U.S. passenger cars typically emit in a year.

Superdome officials had hoped the Super Bowl would showcase to the world the $336 million in renovations that have been made to the stadium since it sustained massive water and wind damage in 2005 due to Hurricane Katrina. Some $156 million of the cost of the renovation was paid by the U.S. Federal Emergency Management Agency. That renovation included work on the stadium's electrical and lighting system, as the Superdome now has a 26,000-LED lighting fixture on 96 concave aluminum panels that ring the building's exterior, a system supported by more than five miles of copper wiring. This system, which draws no more power than a small home, won the 2012 "Excellence in Design" award in the Architainment category from Live Design Magazine, an architecture, design, and event production publication.

LED lights, in addition to being efficient, would be capable of coming on instantly after such an outage. But they are not bright enough to illuminate a field, so they provide only accent lighting. Most stadiums rely on high-intensity gas discharge fixtures for the main lighting of the venue. Such lights take some time to power up to full brightness—a half hour is common.

After emergency generators restored power to the playing field, fans still had to cope with reduced power, with escalators and credit-card machines shut down, and walkways lighted by small banks of light. Broadcasters and NFL officials also had to scramble.

This story is part of a special series that explores energy issues. For more, visit The Great Energy Challenge.