BOULDER CITY, Nev. (KLAS) — A fire Tuesday at the Hoover Dam has made headlines around the world, but the fire did not actually happen on or inside the dam. It happened outside of the Arizona generator powerhouse at an electric transformer.

Inside the Arizona powerhouse are nine massive generators. There are eight generators inside the Nevada powerhouse. While unclear how old the transformer that caught fire is, the generators inside are not the originals.

The power plant as a whole covers two states at the bottom of the Hoover Dam. Electricity, however, was not the driving force to build the dam, that was controlling the Colorado River to be reliably used for irrigation downriver and to supply fresh water to the growing populations of the southwest.

  • Nevada State Museum
  • Hoover_Dam_bypass_bridge_1485206552450.jpg

But the power plant was in no way an afterthought. It was built and completed by 1936, the same time as the dam was complete.

The powerhouses on either side of the river below the dam are not normal buildings. Each building has what was considered at the time to be a bombproof roof. It is 3.6 feet thick with layers of concrete, rock and steel, and surfaced with sand and tar.

By the fall of 1936, the first three generators on the Nevada side began producing power. Two more Nevada generators came online on 1937 and another two in 1938. In 1939 the first two generators on the Arizona side began producing power.

From 1939 to 1947 the Hoover Dam was the largest hydroelectric dam in the world.

Over the next 20 years, another 10 generators were installed, and by December of 1961 the power equipment installation was finally complete at the dam.

This equipment was in use for another 25 years until 1986 when the Bureau of Reclamation began replacing the aging generators. This process took the government seven years to complete.

Generators inside of the Nevada powerhouse at the Hoover Dam. (Photo: Duncan Phenix)


Each power plant wing is 650 feet long (the length of almost 2 football fields) and rises 299 feet (nearly 20 stories) above the power plant foundation. In all of the galleries of the plant, there are 10 acres of floor space.

The power plant has a nameplate capacity of about 2,080 megawatts. This includes the two station-service units (small generating units that provide power for plant operations), which are rated at 2.4 megawatts each. With the main units having a combined rated capacity of 2,991,000 horsepower, and two station-service units rated at 3,500 horsepower each, the plant has a rated capacity of 2,998,000 horsepower.

Currently, there are fifteen 178,000 horsepower, one 100,000 horsepower, and one 86,000 horsepower Francis-type vertical hydraulic turbines in the Hoover power plant. There are also thirteen 130,000 kilowatt, two 127,000 kilowatt, one 61,500 kilowatt, and one 68,500 kilowatt generators. All machines are operated at 60 cycles. The two 2,400 kilowatt station-service units are driven by Pelton water wheels. These provide electrical energy for lights and for operating cranes, pumps, motors, compressors, and other electrical equipment within the dam and power plant.


  • Metropolitan Water District of Southern California – 28.5% of total electrical output
  • Nevada – 23.4%
  • Arizona – 19%
  • Los Angeles, CA – 15.4%
  • Southern California Edison Co. – 5.5%
  • Boulder City, NV – 1.8%
  • Glendale, CA – 1.6%
  • Pasadena, CA – 1.4%
  • Anaheim, CA – 1.1%
  • Riverside, CA – 0.9%
  • Vernon, CA – 0.6%
  • Burbank, CA – 0.6%
  • Azusa, CA – 0.1%
  • Colton, CA – 0.09%


The story of the Hoover Dam – originally the Boulder Dam – can fill the pages of multiple books. But the bottom line was that at the turn of the century people were determined to control the Colorado River.

Control of the river would eventually lead to no flooding downriver and allow farmers in the Imperial Valley to grow produce year-round for the rest of the United States. The area would become known as the Breadbasket of the United States.

1930 – Carrot harvest in the Imperial Valley. (UNLV Digital Collections)

It was only after several failed attempts to dam and divert the Colorado River that the plan for the dam was agreed upon in 1922 when the Colorado River Compact was signed by the seven states along its route.

One of the largest failures to control the Colorado River that can still be seen today was the creation of the Salton Sea in southern California. The sea was formed when a flooding Colorado River breached an irrigation canal being constructed in the Imperial Valley in 1905 and flowed into the Salton Sink.