Rotary system

The rotary machine switching system, or most commonly known as the rotary system, was a type of automatic telephone exchange manufactured and used primarily in Europe from the 1910s. The system was developed and tested by AT&T's American engineering division, Western Electric, in the United States, at the same time when Western Electric was also developing the Panel switch. When AT&T selected the Panel System for large American exchanges, development and sales of the No. 7-A Machine Switching System, its formal commercial name, were transferred to Western Electric's international division in Belgium. In Europe and other continents the system was met with considerable commercial success.

The Rotary and Panel systems were very different systems, but both used the same newly developed component technology, such as Western Electric's latest relays, and the principles of the Lorimer system^[1] of revertive pulsing and preselection.^[2] The Rotary switches were smaller than the Panel system, and served only 200 rather than 500 stations. The initial version was the model 7A. It was succeeded by 7A1 and 7A2 and a rural system had the designation 7D.