By Jonny Lupsha, Wondrium Staff Writer
Thomas Edison and Nikola Tesla’s electricity feud is legendary. While Edison championed direct electrical current, flowing just one way, Tesla worked on alternating current, which flowed in two directions. This week on Wondrium Shorts, electricity gets ugly.
Thomas Edison spent time and money working on electrical current that flowed in one direction, known as direct current (DC). During that time, an employee of his—Nikola Tesla—left Edison’s company to work on current that flowed in two directions, known as alternating current (AC). Edison, not content to let the features and benefits of DC speak for themselves, spent years slandering AC and attempting to show the public that it was dangerous and unfit for home use.
Over the years, the rivalry between AC and DC currents raged and became increasingly ugly. In her video series Engineering School for Everyone: Electrical Engineering, Dr. Laura J. Bottomley, Director of Women in Engineering, Engineering Education, and The Engineering Place at North Carolina State University, describes how the power wars turned unpleasant.
“While Edison was championing DC, another inventor, Nikola Tesla, had left Edison’s company and gone on to acquire several patents concerning AC,” Dr. Bottomley said. “Tesla sold his patents to inventor George Westinghouse, who became Edison’s biggest rival. So began a famous competition for public sentiment over which type of current to use in the electric power distribution system.”
According to Dr. Bottomley, much like Westinghouse, Edison was motivated by his own patents to license DC for widespread use. However, rather than selling DC on its own merits, Edison instead spent his time defaming AC. He participated in large events showing the public that alternating current was unsafe, even using AC to kill large animals live on stage. Edison even took it a step further by working with the state of New York to develop an execution method for prisoners, using AC to prove its danger to the public.
It was known as the electric chair.
High-Voltage DC for Long Distances
So what made AC so unsafe?
“When a person comes into contact with an energized circuit, DC tends to stay on the surface of the skin at higher currents than AC,” Dr. Bottomley said. “AC tends to go under the skin at lower voltages, traveling to the inner organs. It takes nearly six times as much DC to injure a human as it does for AC.”
Ironically, the lack of resistance in alternating current also made it more attractive for long-distance transmission of electric power. According to Dr. Bottomley, AC can be transmitted with less resistive loss of power than DC for distances up to 700 miles. Even the switches that converted voltages from lower to higher values were more expensive when using DC.
“Ironically, several of the things that made AC the choice when transmission systems were first installed have now changed,” she said. “In fact, semiconductor switches and other advances have made it possible for some newer electric systems, particularly some in China, to use high-voltage DC for long-distance links on the order of thousands of kilometers.
“High voltage is far more efficient for transmitting power over long distances.”