The late 1800s was an exciting time for electricity and power transmission. On one side, Thomas Edison championed direct current (DC) as the ideal way to distribute electricity. On the other side, Nikola Tesla advocated for alternating current (AC). This battle became known as the war of the currents.

Edison had the backing of powerful companies that profited from DC power. But Tesla's AC system ultimately won out due to its superior technical advantages. This victory allowed AC power networks to spread rapidly across the United States and the world.

Below I will explore the key factors that led to AC defeating DC in detail. But first, let's overview the main differences between these two types of electrical currents.

Direct Current vs Alternating Current

Direct current (DC) flows in one direction from the power source to the load. The voltage and current stay constant over time.

Alternating current (AC) flows back and forth, constantly changing direction. The voltage and current alternate between positive and negative values.

AC is produced by generators that spin a magnetic coil within wire windings. This creates an oscillating waveform. The frequency of the waveform is typically 50-60 Hz, meaning the current changes direction 50-60 times per second.

Key Advantages of AC:

Key Advantages of DC:

With these differences in mind, let's look at why AC became the dominant form of power transmission while DC faded away.

Edison's Quest to Commercialize Electricity with DC

Thomas Edison built his reputation by pioneering mass-produced electric lighting and the phonograph. By the early 1880s, Edison had established himself as a leading inventor and businessman.

Edison was determined to bring electric lighting to homes and businesses across America. This required a complete system of electric power generation, distribution, and end-use devices.

Edison's Pearl Street Station

In 1882, Edison opened the Pearl Street Station in lower Manhattan. This was the world’s first central power plant, delivering direct current electricity to surrounding buildings.

The Pearl Street dynamos produced DC power at 110 volts. Thick copper wires distributed the current to local users within about a one mile radius. This demonstrated that a centralized power station could provide a safe, reliable alternative to individual generators.

Limitations of Direct Current

However, major limitations of DC soon became apparent:

Edison downplayed these weaknesses and aggressively pushed DC as the supreme electricity delivery method. His company, Edison Electric Light, profited from licensing DC power systems to utilities.

Tesla's Breakthrough: The Induction Motor

Meanwhile, an ambitious inventor named Nikola Tesla immigrated to America in 1884. He began working for Edison but soon struck out on his own.

Tesla had studied AC systems extensively in Europe. He was convinced that AC's ability to step up voltage with transformers gave it a key advantage over DC.

Tesla solves the AC motor problem

However, AC faced a major obstacle - how could motors operate on alternating current? Edison insisted this was impossible and would doom AC systems.

In 1887, Tesla filed patents for an AC induction motor that proved this theory wrong. His motor design eliminated the troublesome commutator and brushes required by DC motors.

The Tesla induction motor could run directly from AC power. This was a monumental breakthrough that helped tip the scales toward the ultimate victory of AC.

Westinghouse Backs Alternating Current

Tesla signed a deal to license his AC patents to the Westinghouse Electric Company. An ambitious entrepreneur named George Westinghouse saw the potential of AC and agreed to promote it.

Lighting the 1893 World's Fair

In 1893, Westinghouse won the bid to light the Chicago World's Fair. He undercut Edison's DC proposal by using AC generators, transformers, and Tesla's induction motors.

This stunning display of AC's capabilities won over the public. People were amazed that a remote AC generator could light the entire fairgrounds with such brilliance.

Niagara Falls project powers industry

Westinghouse's next coup was building a massive hydroelectric AC plant at Niagara Falls in 1895. The plant sent power to industries 25 miles away in Buffalo, New York. This showed AC's viability for long distance transmission.

Within a decade, AC networks crisscrossed America, fueling the second Industrial Revolution. Central stations could now power homes, factories, and streetcars across cities and regions.

Extreme Measures in Edison's "Battle of the Currents"

As AC systems spread rapidly, Edison grew desperate to discredit his new rival. He launched a campaign to portray alternating current as dangerous.

Edison hosts public electrocutions

In 1903, Edison supervised the public electrocution of a circus elephant named Topsy. He fed alternating current through Topsy to demonstrate its killing power.

He also supported developing the electric chair, believing people would associate AC with death. Even though AC ultimately powered the chair, this macabre PR tactic backfired on Edison's reputation.

Direct current has its downsides too

In reality, both direct and alternating current can be lethal in sufficient doses. Edison's smear campaign could not offset AC's proven technical and economic advantages.

AC Powers the World

Despite Edison's prolonged efforts, alternating current proved far superior for transmitting electricity over distances. By the 1910s, AC networks were spreading across cities, regions, and continents.

AC allows interconnection

With AC, power plants could be interconnected, achieving economies of scale. Smaller cities and rural areas could also join these networks.

Higher voltages enable long distance transmission

Using transformers, AC voltage could be cranked up to hundreds of thousands of volts for cross-country transmission with minimal power loss. DC could not achieve such feats.

Thus, AC allowed the creation of robust continental grids while direct current remained restricted to urban centers and individual buildings.

Today, AC provides over 98% of the world's power. Our modern civilization owes a huge debt to Tesla and Westinghouse for realizing AC's potential that Edison tried so hard to suppress.

The Legacy and Return of DC Power

While AC became the standard for electricity transmission, DC never fully disappeared. Its advantages for certain uses kept it entrenched in various niches.

DC powers electronic devices

Most electronics require steady direct current. Today's ubiquitous AC adapters convert household alternating current to power your phones, laptops, and other gadgets.

DC for low voltage grids

DC continues powering lights, equipment, and controls aboard ships, trains, automobiles, airplanes, and spacecraft. These isolated grids run on batteries or DC generators.

High voltage DC transmission

Ironically, high voltage DC (HVDC) lines now transmit huge amounts of power across countries and between grids. HVDC undergoes conversion from AC at either end. This revival makes long distance DC transmission commercially viable once again.


In the war of the currents, Tesla's alternating current defeated Edison's direct current for widespread power distribution. But DC endures for key applications, demonstrating the importance of both technologies. This battle shaped our electrified civilization and still influences how we generate, transmit, and use electricity.