Switchboard cords

The service conditions that a switchboard cord must meet cannot be reproduced mechanically. The paper describes tests which enable, within a reasonable time, comparative data on the probable life of a cord to be obtained for use in the study of suggested improvements in construction. As early as 1878 flexible cords were constructed of tinsel. Since the beginning of the industry cords have followed either one of three forms: (1) Laminated conductors of tinsel threads twisted or braided together; (2) solid conductors of steel or brass wire or tape wound helically; (3) a combination of (1) and (2). In 1910 an alloy tinsel was used in place of commercially pure copper. The six ends of the new tinsel were twisted together instead of being braided, and three such units were twisted into a rope of eighteen threads, and three such, after being insulated, laid up in rope form. In 1912 a tinsel cord was produced treated with compound, which made the cord moisture-proof without sacrificing its flexibility. The resistance of the cord was 9/10 ohm for a 6-ft. cord, and 12,000 operations were necessary before any one of the three conductors became noisy. Photographs of the various cords and specification of the tinsel thread accompanies the paper.