National Geographic : 1941 Apr
Maryland Presents- 439 Photograph by Holmes I. Mettee One by One She Tests the 300 Pairs of Wires in a Telephone Cable For each hundred pairs of wires an additional pair is added against possible breakage of a line. Some cables of this same size contain as many as 4,242 wires. They are insulated with different-colored threads for identifica tion. Transmission cables for television also are manufactured in this Western Electric Company plant at Baltimore.