Texas shed 20,000 megawatts in 2021, and its links to other grids carry 1,220

Sep 22, 2026

Map of North America's power grid showing the Western, Eastern, Texas and Quebec interconnections and the regional reliability councils as of 2009 — Credit: Bouchecl, Wikimedia Commons, CC BY-SA 3.0 · Source ↗

In February 2021, the operator of the Texas grid ordered 20,000 megawatts of rolling blackouts, the largest manually controlled load shed in US history. The lines connecting that grid to the rest of the continent add up to about 1,220 megawatts, by ERCOT's own count.

That gap exists because Texas runs a grid of its own, one of three in the lower 48, and the edges of all three follow no state line.

One country, three grids

The Department of Energy describes the grid serving the lower 48 as three interconnections. Inside each one, every generator runs in lockstep at an average of 60 hertz. Between them, nothing is synchronized.

The Eastern Interconnection runs from central Canada to the Atlantic, south to Florida and west to the foot of the Rockies, leaving out Québec and most of Texas. The Western Interconnection stretches from western Canada to Baja California in Mexico and reaches east over the Rockies onto the Great Plains. The Texas Interconnection covers most of Texas.

Like time zones, the seams cut through states.

Where the seams are

Map of high-voltage transmission lines across the United States — Credit: Wikideas1, Wikimedia Commons, CC0 · Source ↗

Two grids that aren't synchronized can't be wired together directly. Power crosses between them through converter stations that turn alternating current into direct current and back again.

Just east of the Rockies, a string of these back-to-back converters lets 1,320 megawatts flow between the Eastern and Western grids. The DOE calls that "small compared to the size of the two networks."

ERCOT counts two DC ties with the Southwest Power Pool, worth 820 megawatts combined, and a DC tie plus a variable frequency transformer with Mexico's grid operator, CENACE, worth 400 megawatts.

Texas isn't all ERCOT

ERCOT delivers about 90% of the electricity used by more than 27 million Texans and covers about 75% of the state's land. The rest of Texas plugs into the other two grids.

The Texas Almanac draws the lines: the Panhandle, the South Plains and a corner of Northeast Texas belong to the Southwest Power Pool, on the Eastern grid. The southeast corner belongs to SERC, which sits in the Eastern Interconnection too; El Paso and the far western Trans-Pecos run on the Western grid. ERCOT's own list of exclusions names Longview, Marshall, Texarkana, Beaumont, Port Arthur and The Woodlands.

That puts El Paso on the Western grid, Beaumont on the Eastern and Houston on ERCOT's: three Texas cities on three grids that aren't synchronized with each other.

ERCOT control room operator at a dispatch console with wall displays — Credit: Dpysh w, Wikimedia Commons, CC BY 3.0 · Source ↗

Why Texas kept to itself

The Baker Institute's history starts in 1935. The Federal Power Act let the Federal Power Commission regulate wholesale interstate power sales and order utilities to interconnect. Power that never crossed a state line stayed outside that reach.

Texas did connect, in wartime. In 1942 the commission offered relief from federal regulation to utilities joining interstate networks for war industries, and 16 Texas companies joined the Southwest Power Pool, which ran from Nebraska to South Texas.

The in-state systems later consolidated. North and South Texas merged in 1967 into what became the Texas Interconnected System, and in 1970 its utilities organized ERCOT, committed to serving only the Texas market.

Then, on May 4, 1976, West Texas Utilities wired its circuits to Public Service Company of Oklahoma overnight. Two utilities answered by pulling off the Texas grid. Houston Lighting & Power and Texas Electric Service Company did it, the Baker Institute writes, "explicitly to avoid falling under federal regulation against their will."

Julie Cohn, the author, puts the isolation down mostly to protecting business interests, preserving internal reliability and avoiding extra costs, with Texas pride a smaller factor.

February 2021

NASA satellite image of Houston's lights at night on February 7, 2021, before the blackouts — Credit: NASA Earth Observatory · Source ↗

NASA satellite image of Houston at night on February 16, 2021, with large areas dark during the blackouts — Credit: NASA Earth Observatory · Source ↗

Winter Storm Uri knocked out more than 4.5 million Texans' power, some for as long as four days. The FERC and NERC final report traced 75.6% of unplanned generator outages to two causes: equipment freezing (44.2%) and fuel supply problems (31.4%). The Texas Department of State Health Services later put the death toll at 246, most from hypothermia.

The neighbors had little to spare. On February 15 the Southwest Power Pool ordered the first controlled interruptions in its history, and MISO had Entergy cut 800 megawatts in its western load pocket that morning, with more the next day.

The FERC report's own fix is winterization. Protecting four types of plant components, it found, could have cut outages by 67% in the ERCOT region.

Stitching the map together

ERCOT lists the proposed Southern Spirit line, up to 3,000 megawatts, to link Texas with grids to the southeast.

Between East and West, the DOE-funded Interconnections Seam Study found that raising transfer capacity returns at least $1.25 in net benefits for every dollar spent, and up to $2.90 in some scenarios.

Want to sketch the three grids yourself? Start from our free blank US state map.