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"The electrical grid is still basically 1960s technology," says physicist Phillip F. Schewe, author of The Grid. "The Internet has passed it by. The meter on the side of your house is 1920s technology." Sometimes that quaintness becomes a problem. On the grid these days, things can go bad very fast.

When you flip a light switch, the electricity that zips into the bulb was created just a fraction of a second earlier, many miles away. Where it was made, you can't know, because hundreds of power plants spread over many states are all pouring their output into the same communal grid. Electricity can't be stored on a large scale with today's technology; it has to be used instantly. At each instant there has to be a precise balance between generation and demand over the whole grid. In control rooms around the grid, engineers constantly monitor the flow of electricity, trying to keep voltage and frequency steady and to avoid surges that could damage both their customers' equipment and their own.

When I flip a switch at my house in Washington, D.C., I'm dipping into a giant pool of electricity called the PJM Interconnection. PJM is one of several regional operators that make up the Eastern grid; it covers the District of Colum­bia and 13 states, from the Mississippi River east to New Jersey and all the way down to the Outer Banks of North Carolina. It's an electricity market that keeps supply and demand almost perfectly matched—every day, every minute, every fraction of a second—among hundreds of producers and distributors and 51 million people, via 56,350 miles of high-voltage transmission lines.

One of PJM's new control centers is an hour north of Philadelphia. Last February I went to visit it with Ray E. Dotter, a company spokesman. Along the way Dotter identified the power lines we passed under. There was a pair of 500-kilovolt lines linking the Limerick nuclear plant with the Whitpain substation. Then a 230-kilovolt line. Then another. Burying the ungainly lines is prohibitively expensive except in dense cities. "There's a need to build new lines," Dotter said. "But no matter where you propose them, people don't want them."

Dotter pulled off the turnpike in the middle of nowhere. A communications tower poked above the treetops. We drove onto a compound surrounded by a security fence. Soon we were in the bunker, built by AT&T during the Cold War to withstand anything but a direct nuclear hit and recently purchased by PJM to serve as its new nerve center.

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