William Stanley Jr.

William Stanley Jr. was an American engineer who in 1886 built and publicly demonstrated a practical alternating current transformer and a complete AC distribution system in Great Barrington, Massachusetts, the first commercial demonstration in the United States that alternating current could be generated at one voltage, stepped up for efficient long-distance transmission, and then stepped back down to a safe voltage for use in homes and shops. Stanleys demonstration, powering around two dozen buildings along the towns main street, proved to American investors and engineers that George Westinghouses AC system was commercially practical, directly influencing Westinghouses decision to pursue AC over Edisons competing direct current system in the war of the currents. Stanleys transformer design, refined in the years that followed, became the basic technology used to step voltage up and down throughout every alternating current power grid built afterward. His Great Barrington demonstration is regarded as the proof-of-concept moment that made the modern long-distance AC power grid commercially credible.