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Strowger calling dial, 1900
Strowger calling dial, made by the Automatic Electric Company, United States, 1900.
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This calling dial was the first design to use the 'three wire' system which had an earth connection in addition to the two telephone lines connecting to the exchange. Dialling impulses were sent alternately along the two exchange wires, and the earth connection provided the return path. The 'three wire' system was standard until 1907.
- Materials:
- metal (unknown)
- Object Number:
- 1926-1057/1
- type:
- telephone component
- Image ©
- The Board of Trustees of the Science Museum
