Excerpt from Transactions of the New York Electrical Society, Vol. 6: Modern Telephone Engineering; Lecture Delivered Before the New York Electrical Society, February 14, 1901
The size 'of the section is limited by the reach of the operator, and it is this fact that places a ... mechanical limit to the size of an ordinary multiple switchboard. It has been found impracticable in most cases to place the jacks closer than on half-inch centers, and under these conditions no more than six thousand (6000) of the multiple jacks could be placed, in addition to the other apparatus, within the space afforded by one section.
Two distinct methods have been followed with the intent of removing this limit. Each has been productive of excel lent results; each has been used separately, but up to the present time they have not both been incorporated into the same installation. The first of these methods is an obvious one and contemplates the reduction in the size of the spring jacks with a view to getting more of them within the reach of the operator. The mechanical difficulties in this line have been great, owing to the fact that the circuits of the switchboard were so complicated as to require three. Four, and sometimes even five contacts to each spring jack. The Western Electric Company in the Paris board succeeded in reducing the dimensions of the jack to three-eighths of an inch (g-in.) centers, both horizontally and vertically, and thus rendered practicable the installation of a switchboard having a capacity for considerably over nine thousand (9000) lines. I believe that there are other boards which have been installed with success having this size of jack, and that others are at present in course of construction for large cities in this country. This jack had three contacts, and I believe is the smallest that has ever been put into ex tensive use.
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