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Con Edison Media Relations
For Immediate Release: November 14, 2007
4:53 PM

A/C BUT NO D/C: LAST CON EDISON DIRECT CURRENT CUSTOMER IS HISTORY

Utility Retires Direct Current System with a Ceremonial Cable Snip

NEW YORK - Con Edison’s Electric Operations Manager Fred Simms, an active employee for 52 years, cut a ceremonial cable on 40th Street just east of Fifth Avenue today to retire the utility’s direct current (DC) service. The supply of DC service to New York customers dates back 125 years, to the advent of Thomas Edison’s first electric generating station on Pearl Street in 1882.

Thomas Edison's method for generating and transmitting electricity was called direct current, or low voltage. George Westinghouse, a consolidator of his time, built Westinghouse Electric by purchasing other inventors’ patents, including the polyphase alternating current (AC) system invented by Nikola Tesla.

In an alternating current system, transformers were used to step up, or increase the voltage that left the power plant. This enabled the electricity to travel over long-distance wires. When the electricity reached its destination, another transformer would then step down, or decrease, the voltage so that power could be used in homes and factories.

Edison's direct current system was unable to use transformers. With Edison's system, the voltage dropped as it traveled further and further from the generator. To overcome this disadvantage, power plants would have to be built close to the power users – a costly solution.

Alternating current eventually gained prevalence over direct current in utility systems for that reason. The company froze the development of the DC system in 1928, attempting to continue to supply New York’s major DC customers without investing any more funds in major improvements or expansions of the system.

Direct current systems are still universally used in vehicles for engine starting, lighting, ignition, and battery charging. Most electric railways use a DC third-rail system, although trains powered by overhead pantographs use AC.

Some cities retained their DC networks for varying periods of time. For example, central Helsinki had a DC network until the late 1940s, and Stockholm lost its diminishing DC network in the ´60s. Con Edison continued to supply direct current to customers, mainly for elevators, but with DC burnouts a continuing and expensive maintenance problem. In the mid-1960s, Con Edison started to install 250 kilowatt rectifiers in the street and 150 kilowatt rectifiers in large buildings to mitigate maintenance costs.

The number of DC services remaining in the early 1970s was approximately 5,700, supplying over 6,000 customers stretching from the Battery to 132nd St. in Harlem.

In January 1998, Consolidated Edison began a program to eliminate DC service in its operating territory. At that time there were over 4,600 DC customers. By 2006, sixty remained. Between then and today, when the last customer at 10 East 40th Street was switched to rectifiers on their side of the meter to generate direct current to supply its building’s elevators and sprinkler system, Con Edison has been switching DC customers to alternating current.

Since the start of the program in January 1998:

  • 4,541 accounts in 4,288 buildings have been converted;
  • 6,172 DC meters have been removed from the system;
  • 193 in-building rectifiers have been transferred to customers;
  • 148 250KW street rectifiers have been removed;
  • 35,965 sections of DC mains (5,682,337 circuit feet or 2,660,634 cable feet) has been retired; and
  • 545,185 circuit feet or 236,611 cable feet of DC services has been retired.
Con Edison is a subsidiary of Consolidated Edison, Inc. [NYSE: ED], one of the nation’s largest investor-owned energy companies, with approximately $12 billion in annual revenues and $28 billion in assets. The utility provides electric, gas and steam service to more than 3 million customers in New York City and Westchester County, New York. For additional financial, operations and customer service information, visit Con Edison’s Web site at www.coned.com.

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