A short list of well-known facts about how electricity reaches homes and businesses in the United States.
Three separate grids
The power grid in the lower 48 states is split into three main interconnections: the Eastern Interconnection, the Western Interconnection, and the Texas Interconnection run by ERCOT. They are linked to each other by only a small number of direct-current ties.
60 cycles per second
The North American grid runs on alternating current at 60 hertz. Much of Europe and Asia uses 50 hertz instead.
Hundreds of thousands of miles of wire
The US bulk grid has over 360,000 miles of transmission lines, including about 180,000 miles of high-voltage lines.
Voltage steps up and down
Transmission lines commonly carry power at 115,000 to 765,000 volts. Transformers step that down for local distribution, and most homes receive 120/240 volts.
Thousands of power plants
The US has over 10,000 utility-scale power plants, all feeding the same interconnected network.
Supply must match demand every second
The grid stores very little energy, so generation has to match consumption in real time. When the two drift apart, the grid's frequency moves away from 60 hertz, and operators must add or shed supply to bring it back.
Large power transformers are giants
Large power transformers can weigh 100 to 400 tons, are usually custom-built for one location, and often stay in service for 40 years or more.
Most power passes through one
An estimated 90 percent of the electricity used in the US passes through a large power transformer at some point on its way to the user.
Replacement takes years
Lead times for a new large power transformer are now commonly about three years, and can reach five years.
Reliability standards
The North American Electric Reliability Corporation (NERC) sets and enforces reliability standards for the bulk power system across the US, Canada, and part of Mexico.
The 2003 Northeast blackout
On August 14, 2003, a cascading failure cut power to about 50 million people across the northeastern and midwestern US and Ontario, Canada. Some areas were dark for days.
Texas, February 2021
During Winter Storm Uri in February 2021, over 4.5 million homes and businesses in Texas lost power as extreme cold knocked generation offline while demand surged.
The Carrington Event of 1859
The strongest geomagnetic storm on record struck in September 1859. Telegraph systems failed or sparked, and auroras were seen as far south as the Caribbean.
Quebec, March 1989
A geomagnetic storm in March 1989 collapsed the Hydro-Québec grid in about 90 seconds, leaving about 6 million people without power for roughly nine hours.
A huge yearly load
The US uses about 4 trillion kilowatt-hours of electricity each year.