It began on Aug. 14, 2003 when an overloaded power transmission line fell on a tree branch in Ohio and a computer glitch kept grid operators at FirstEnergy Corp. in Ohio from recognizing or understanding what was happening. It ended in the biggest power blackout in US history, affecting 55 million people in eight states and parts of Canada, with an estimated cost of nearly $10 billion. What started as a minor local event cascaded into the loss of 61.8 gigawatts of power, including output from 19 nuclear reactors at 10 plants. It took about 30 hours to substantially return power to the 10 million affected in Canada and 45 million in the US, although some areas were not restored for two days. Ten years on, better management of the US grid makes it less likely such an event will recur. While the grid remains vulnerable to severe storms like Hurricane Sandy — which left an estimated 8 million people in the eastern US without power last October — or to cyber attacks, the number of outages caused by faulty equipment or human error has fallen.
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