Western Electric main-line telegraph relay

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Telegraph relays amplified electrical signals in a telegraph line. Telegraph messages traveled as a series of electrical pulses through a wire from a transmitter to a receiver. Short pulses made a dot, slightly longer pulses a dash. The pulses faded in strength as they traveled through the wire, to the point where the incoming signal was too weak to directly operate a receiving sounder or register. A relay detected a weak signal and used a battery to strengthen the signal so that the receiver would operate.
“Main line” relays like this Western Electric unit were one of the most common types of relay and, as seen in this piece, were typically made with a resistance of 150 ohms. As the name suggests, main line relays served on major intercity circuits several hundred miles long. Better known for their Bell System telephone equipment, Western Electric manufactured a wide range of electrical devices.
Currently not on view
Western Electric
Physical Description
wood (overall material)
brass (overall material)
steel (overall material)
plastic (overall material)
overall: 3 1/4 in x 8 1/2 in x 4 1/2 in; 8.255 cm x 21.59 cm x 11.43 cm
ID Number
catalog number
accession number
collector/donor number
Credit Line
from Western Union Corporation
See more items in
Work and Industry: Electricity
Telegraph Relays & Repeaters
Data Source
National Museum of American History