The best utilities in the country deliver electricity to customers about 99.99 of the time. Sometimes referred to as "four nines" reliability, 99.99-percent power reliability is considered excellent by industry measures. But for some pharmaceutical firms, health-care facilities or credit-card companies, even having electricity 99.99 percent of the time isn't good enough. Such customers operate at five or six "nines" of reliability -- 99.999 or even higher.
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