North American electricity grid

 DOELong distance power transmission lines. Source: DOE

The North American electricity grid is the world's largest and most complex system of power generation, transmission, and distribution. The grid delivers electricity to almost all the people in the U.S., Canada and a portion of Baja California Norte, Mexico. This market generates an electricity demand of about 830 gigawatts (GW) (830,000 megawatts). The North American grid has 211,000 miles (340,000 km) of high-voltage transmission line (230,000 volts and greater), and total assets of more than $1 trillion (US).

By way of contrast, the next largest electricity grids are Europe (781 GW), China (391 GW), Japan (243 GW), Russia (216 GW), and India (131 GW). The U.S. Energy Information Administration expects electricity consumption in China to increase from 1.7 billion kilowatt-hours in 2030 to more than 10 billion kilowatt-hours in 2030, by which time it may surpass North America's grid as the world's largest.

Most electricity grids have three components: generation, transmission, and distribution. Most electricity in North America is generated in large power plants that burn a fuel (coal, oil, natural gas), split atoms (nuclear), or use falling water (hydropower) to generate electricity. An increasing quantity of power is generated by renewable sources such as wind and so-called distributed sources, that is, the small-scale production of electricity at or near customers' homes and businesses. Distributed generation can come from conventional technologies, such as motors powered by natural gas or diesel fuel, or from renewable technologies, such as solar photovoltaic cells.

The U.S. operates about 10,000 power plants and another approximately 5,600 distributed energy facilities.

The high-voltage transmission system carries electricity from the power plants and transmits it up to hundreds of miles away. High voltage is used for transmission lines to minimize electrical losses.

The transmission system truly is a grid. Transmission lines run not only from power plants to load centers but also from transmission line to transmission line, providing a redundant system that helps ensure the smooth flow of power. If a transmission line is taken out of service in one part of the power grid, the power can usually be rerouted through other power lines to continue delivering power to customers.

In essence, the power from many power plants is "pooled" in the transmission system, and each distribution system draws from this pool. This networked system helps achieve a high reliability for power delivery because any one power plant that shuts down will only constitute a fraction of the power being delivered by the grid.

One result of power pooling is that the electricity drawn off the grid always comes from a diversity of power sources, which may include coal, nuclear, natural gas, oil, and renewable energy sources such as hydropower, biomass, wind, and solar power. This is often referred to as "system power" because it is the standard power mixture that supplies the transmission system.

The lower-voltage distribution systems draw electricity from the transmission lines and distribute it to individual customers. The interface between the two is the electrical substation, which features transformers that "step down" the transmission voltages-ranging from 138 kV to 765 kV-to lower voltages for the distribution systems. Transformers located along the distribution lines further step down the voltage to 120 V or 240 V for household use.

The North American system of electricity generation, transmission, and distribution has been called the world's biggest machine. It physically and administratively subdivided into three "interconnects"- the Eastern, covering the eastern two-thirds of the United States and Canada; the Western, encompassing most of the rest of the two countries; and the Electric Reliability Council of Texas (ERCOT), covering most of Texas.

Both the Western and Texas Interconnects are linked with Mexico, and the Eastern and Western Interconnects are strongly interconnected with Canada. All electric utilities in the mainland United States are connected with at least one other utility via these power grids.

Within each interconnect, power flows through AC lines, so all generators are tightly synchronized to the same 60-Hz cycle. The interconnects are joined to each other by DC links, so the coupling is much looser among the interconnects than within them. (The capacity of the transmission lines between the interconnects is also far less than the capacity of the links within them.)

 DOEThe Regional Reliability Councils managed the North American Electric Reliability Corporation (NERC). Source: DOE

The grid is managed by the North American Electric Reliability Corporation (NERC), a self-regulatory organization based in Princeton, New Jersey, whose stated mission is to "improve the reliability and security of the bulk power system in North America." Among other activities, NERC develops and enforces reliability standards; monitors the bulk power system; assesses future adequacy; audits owners, operators, and users for preparedness; and educates and trains industry personnel. NERC works with eight Regional Reliability Councils that represent virtually all the electricity supplied in the United States, Canada, and a portion of Baja California Norte, Mexico:

  • Electric Reliability Council of Texas, Inc. (ERCOT)
  • Florida Reliability Coordinating Council (FRCC)
  • Midwest Reliability Organization (MRO)
  • Northeast Power Coordinating Council (NPCC)
  • ReliabilityFirst Corporation (RFC)
  • SERC Reliability Corporation (SERC)
  • Southwest Power Pool, Inc. (SPP)
  • Western Electricity Coordinating Council (WECC)

NERC is subject to audit by the U.S. Federal Energy Regulatory Commission and governmental authorities in Canada.

NERC's members are the eight Regional Reliability Councils whose members come from all segments of the electric industry: investor-owned utilities; federal power agencies; rural electric cooperatives; state, municipal and provincial utilities; independent power producers; power marketers; and end-use customers. These entities account for virtually all the electricity supplied in the United States, Canada, and a portion of Baja California Norte, Mexico.

The Eastern and Western Interconnects have limited interconnections to each other, and the Texas Interconnect is only linked to the others via direct current lines. Both the Western and Texas Interconnects are linked with Mexico, and the Eastern and Western Interconnects are strongly interconnected with Canada. All electric utilities in the mainland United States are connected to at least one other utility via these power grids.

The North American power system has experienced three major blackouts:

 ©Allan TannenbaumThe darkened New York City skyline at dawn due to the blackout of 1977. Credit: ©Allan Tannenbaum

  • November 9, 1965: an outage caused by a faulty relay at a power plant in Ontario, affected 30 million people over an area of 207,000 km2 (about 80 000 mi2) from eastern Ontario through New York State and much of New England for periods ranging from a few minutes to 13 hours.
  • July 14, 1977: A lightning strike causes widespread power outages in New York City and Westchester County. Electric service to more than 8 million people in the metropolitan are and to the commercial and industrial users in this area was interrupted from 5 to 25 hours.
  • August 14, 2003: the North American power grid experiences its largest blackout ever. The blackout affected an estimated 50 million people and more than 70,000 megawatts (MW) of electrical load in parts of Ohio, Michigan, New York, Pennsylvania, New Jersey, Connecticut, Massachusetts, Vermont, and the Canadian provinces of Ontario and Québec. Although power was successfully restored to most customers within hours, some areas in the United States did not have power for two days and parts of Ontario experienced rotating blackouts for up to two weeks.


  • Casazza, J. A.; Delea, F. Understanding Electric Power Systems: An Overview of the Technology and the Marketplace; Wiley: New York, 2003; 300 pp.

  • North American Electric Reliability Corporation, Understanding the grid, Accessed 6 September 2008.
  • U.S. Department of Energy, Office of Electricity Delivery and Energy Reliability, Overview of the Electric Grid, Accessed 6 September 2008.

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