base for Strowger calling dial, 1900

1900 in United States

Base from Strowger calling dial, made by the Automatic Electric Company, United States, 1900.

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.

On display

Science Museum: Information Age Gallery: Exchange

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Object Number:
With mount attatched: 320 mm x 210 mm x 105 mm, 1.18 kg
Without mount: 135 mm x 210 mm x 105 mm,
telephone component
  • component - object
  • telephone
Donated by BT Heritage and Archives

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