The Nation: WHY THE LIGHTS WENT OUT

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In the past, this deficit might have kayoed the entire Con Ed system and blacked out nearby areas as well. But safety devices and procedures adopted after the 1965 blackout automatically went into action—at first reducing voltages supplied to customers by 5%, then by 8%. Lights flickered and television pictures shrank. Still, the maneuver temporarily staved off the complete shutdowns that the devices would otherwise have ordered to protect the generators and transformers from being burned out by dangerous overloads.

The voltage reduction also gave the control center time to call upon other power plants in the city to feed in more electricity. By revving up their turbines, they were quickly able to make up about 1,000 megawatts. Still, that was hardly enough. So the computers, acting on preprogrammed instructions, made a calculated tradeoff: to keep the city's vital subways, hospitals, elevators and other services running, they began ''shedding load"—reducing electrical demand—by blacking out several less populated suburban bedroom communities in West-Chester. Presumably, that would give Con Ed controllers time to call in more energy from elsewhere.

For a few minutes, the stratagem worked. But a new problem developed on the utility's eastern flank. Because Con Ed's great drain of power was overheating their connecting cables, the neighboring Long Island Lighting Co unplugged from the system. That left Con Ed with only three major sources of electricity: its often troublesome 1,000-megawatt "Big Allis" (for Allis-Chalmers) generator in the borough of Queens and two remaining out-of-state links—one to New Jersey's Public Service Gas & Electric Co., the other to upstate and New England utilities.

Incredibly, at about 9:27, still more lightning in Westchester cut off Con Ed's last remaining hookup to the north. Moments later, as they staggered under this additional demand, Big Allis was shut off by its automatic switches, and New Jersey also cut itself free. Thus the city was isolated from any outside sources of power because of the very safety arrangements made after the 1965 blackout. Only a handful of small local power stations were left to meet the overwhelming electrical load. By 9:41 even the last of these shut off.

The breakdown took little more than an hour, but the restoration of power was far more tedious. Though the equipment itself was undamaged, protective circuit breakers—many of them underground—automatically tripped and had to be individually examined and reset. In addition, since 1965, Con Ed has shut down several of its old local coal-fired plants. Thus it is forced to draw on generators far outside the city that are more difficult to reconnect into the system. Finally, no more than a single section of the city could be powered up at a time for fear of a new overload. In all, it was 25 hours before all the equipment could be brought back on line and the lights came on again.