Electricity powers our world, yet few people stop to consider why the electricity in our wall sockets is Alternating Current (AC), not Direct Current (DC). The answer lies in one of the greatest technological rivalries of all time: the War of Currents—a battle between Thomas Edison and Nikola Tesla that shaped the modern electrical grid.

While Edison championed Direct Current (DC), Tesla promoted Alternating Current (AC) as the superior solution. The debate wasn’t just theoretical—it had real consequences, from animal electrocutions to the electric chair, all in an effort to sway public opinion.

The Rise of Edison’s DC Empire

In the late 1800s, Thomas Edison was already a renowned inventor, with the light bulb as his crowning achievement. But a light bulb is useless without power, so Edison set out to build an electrical grid based on Direct Current (DC). DC electricity flows in one direction—like water moving through a pipe. It works well for batteries and short-distance transmission, but it has a major drawback:

• Voltage drops significantly over long distances.
• This means power plants had to be built every mile or two to keep the voltage high enough for homes and businesses.

Despite these limitations, Edison was determined to make DC the standard and invested heavily in its development.

Nikola Tesla and the War of Currents

Nikola Tesla, an eccentric Serbian-American engineer who had a radically different vision. He saw the flaws in DC and believed that Alternating Current (AC)—which changes direction many times per second— was a better alternative. Tesla’s key insight was that AC could be transformed to higher or lower voltages using a transformer. This was a game-changer for electricity distribution. However, edison was not willing to step down. Edison was a firm believer in Direct Current (DC) and had invested heavily in DC-based infrastructure.

The battle between Thomas Edison and Nikola Tesla over electrical supremacy—now known as the War of Currents—was more than just a technological rivalry. It became a public relations war, and Edison fought dirty. Edison was a firm believer in Direct Current (DC) and had invested heavily in DC-based infrastructure. However, Tesla, backed by George Westinghouse, demonstrated that Alternating Current (AC) was far superior for long-distance power transmission. AC could be stepped up to high voltages for efficient transmission and then stepped down for safe household use—something DC simply couldn’t do.

Realizing that AC threatened his investments, Edison embarked on a fear-mongering campaign to convince the public that AC was dangerous. Since AC operated at higher voltages, Edison used it as a scare tactic, arguing that it was too deadly for home use. Edison’s team, led by electrical engineer Harold P. Brown, began staging gruesome experiments to showcase the dangers of AC. They would publicly electrocute stray dogs, horses, and even cattle, using high-voltage AC. These horrifying demonstrations were meant to show that AC could instantly kill and therefore should not be used for everyday electrical applications.

One of the most disturbing events occurred in 1903, when Edison’s team electrocuted Topsy the elephant at Coney Island’s Luna Park. The 6-ton elephant had a history of aggression after years of mistreatment, and park officials decided to euthanize her. Edison saw an opportunity and offered to execute Topsy using AC electricity. Before a large crowd—and with cameras rolling—the elephant was killed using 6,600 volts of AC. The footage was later distributed to further demonize AC power.

Edison’s campaign also extended into capital punishment. He secretly funded the development of the first electric chair, ensuring it was powered by AC. His goal was clear: if AC was deadly enough for executions, surely it wasn’t safe for homes. In 1890, convicted murderer William Kemmler became the first person to be executed by electrocution. The process was horrific and prolonged, but Edison used it as further evidence that AC was too dangerous for daily use.

Despite Edison’s brutal campaign, the efficiency of AC was undeniable. The Chicago World’s Fair of 1893 was powered entirely by Tesla’s AC system, impressing millions. Then, in 1895, Tesla and Westinghouse completed the Niagara Falls Power Plant, proving that AC could power entire cities. Edison’s smear campaign ultimately failed. AC became the global standard, and Edison’s DC power systems faded into history. However, Edison’s tactics left a dark stain on the history of electricity. The public electrocutions remain one of the most disturbing moments of the industrial age—showing just how far Edison was willing to go to win.

Why AC Won

Nikola Tesla’s revolutionary vision for AC power was based on its ability to be transformed to different voltages using transformers, which made it practical for long-distance transmission. AC could be stepped up to high voltages for efficient transmission and then stepped down for safe household use—something DC simply could not do.

Understanding Transformers: How AC Became Practical

A transformer is an electrical device that changes the voltage of an alternating current (AC) by using electromagnetic induction. It consists of two main components:

1. Primary Coil – The coil that receives the input AC voltage.
2. Secondary Coil – The coil that delivers the output AC voltage.

These coils are wrapped around a core made of iron or ferrite, which enhances the magnetic field.

How It Works:

1. Electromagnetic Induction – When an AC current flows through the primary coil, it creates a changing magnetic field around it.
2. Magnetic Coupling – Changing magnetic field induces a voltage in the secondary coil through Faraday’s Law of Induction.
3. Voltage Transformation – The ratio of the number of turns in the primary coil to the secondary coil determines whether the voltage is increased (step-up transformer) or decreased (step-down transformer).

$$\frac{V_{\text{secondary}}}{V_{\text{primary}}} = \frac{N_{\text{secondary}}}{N_{\text{primary}}}$$

Where:

• V_primary and V_secondary are the voltages in the primary and secondary coils
• N_primary and N_seconday are the number of turns in each coil

Step-Up vs. Step-Down Transformers

• Step-Up Transformer: N_secondary > N_primary, increasing the voltage.
• Step-Down Transformer: N_secondary < N_primary, decreasing the voltage.

This ability to change voltages efficiently is why AC power grids use transformers, allowing for high-voltage transmission with minimal energy loss over long distances, then stepping down to safer voltages for home use.

Why AC is Superior for Long-Distance Transmission

The biggest advantage of AC is that it allows power to be transmitted at high voltage and low current, which reduces energy loss over long distances. In transmission lines, power loss occurs due to resistance in the line, which is in series with the source. By keeping the current in the circuit low, power losses can be minimized, as the loss based on the Joule’s law is,

$$P_{\text{loss}} = I^2 R$$

Where:

• P_loss = Power lost as heat in the transmission lines
• I = Current flowing through the wire
• R = Resistance of the wire

Similarly, according to Joule’s law, power is P = UI. By maintaining a high voltage, large amounts of power can be transmitted with minimal energy loss in the lines. As earlier described, using transformers, AC voltage can be increased before transmission—high voltage means lower current for the same power level. Since power loss depends on I², lowering the current significantly reduces transmission losses. Once AC reaches its destination, another transformer steps it down to a safe voltage for homes and businesses.

This is why modern power grids use very high voltages (often 100,000 volts or more) for long-distance transmission, then step it down to 120V or 230V for household use. DC, on the other hand, lacks an easy way to step up and down voltages efficiently, making it impractical for large-scale grids.

While AC dominates power grids, DC never of course disappeared. DC is still used in many application and it is also making a comeback in certain power grids such as high-voltage DC transmission lines, which have certain benefits compared to AC counterparts. For example, most of the underwater power cables are DC.

Final thoughts

The War of Currents wasn’t just a battle between AC and DC—it was a clash of innovation, business empires, and ruthless tactics. Tesla and Westinghouse won the war, giving us the AC power grid we rely on today. Edison lost, but DC still thrives in batteries, electronics, and high voltage transmission lines. Future grids may combine the best of both worlds—using AC for homes and DC for efficient energy transmission. Maybe history isn’t finished with this battle just yet.

More Information

For those who want to dive deeper into the battle between Tesla and Edison, here are two excellent books:

1. “Empires of Light: Edison, Tesla, Westinghouse, and the Race to Electrify the World” by Jill Jonnes – This book provides a compelling narrative of the fierce battle between these inventors and entrepreneurs as they fought to control the future of electricity. It covers their innovations, business struggles, and the larger-than-life personalities that shaped the modern world. Amazon
2. “Tesla vs Edison: The Life-Long Feud that Electrified the World” by Nigel Cawthorne – This book focuses on the intense personal and professional rivalry between Tesla and Edison, exploring their opposing visions for electrical power and how their competition ultimately shaped technological progress. Amazon

These books offer in-depth insights into the scientific, business, and ethical battles that defined the War of Currents and continue to influence the electrical industry today.