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USA 250 Series 45: Automatic Telephone Exchange Expansion
After the first commercial Strowger automatic exchange opened in La Porte, Indiana, in 1892, larger and more refined systems spread through independent telephone companies in the early 1900s. Automatic Electric Company installed step-by-step exchanges that handled hundreds and then thousands of lines. A 900-line exchange went into service in Augusta, Georgia, in 1897, and a 10,000-line rotary-dial exchange opened in Chicago in 1903. Each subscriber dialed the number; pulses from the dial stepped the selectors until the called line was connected.
Manual switchboards with operators already connected calls in most cities. The expanding automatic systems replaced the operator’s plug-and-jack work for local calls with electromechanical selectors that the caller controlled directly. Independent companies adopted the equipment first. Bell System engineers later developed Panel and Rotary switches better suited to the dense traffic of large cities, while the basic step-by-step principle continued in smaller exchanges for decades.
The expansion of automatic exchanges did not invent telephone switching. It scaled the Strowger selector from small installations to city-sized exchanges so that subscribers could complete local calls without an operator. This is Invention #045 in Automation History’s America 250 series. The entry treats the early-1900s growth of step-by-step and related automatic systems as the practical extension of the 1891–1892 Strowger switch rather than the automatic origin of modern digital switching, with sources and the distinction between the first small exchanges and the larger installations of the 1900s noted. Free reading of this and the rest of the series is at America 250 45: Automatic Telephone Exchange Expansion — Automation History
