TELEPHONE SYSTEM OF THE UNITED STATES 



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cables are spliced in the cable vault to smaller units of silk and cotton 

 insulated conductors which extend up through the building in slots 

 or ducts to the main distributing frame. 



Switching Systems 



The outstanding development in switching systems for a telephone 

 communication has, of course, been the rapid trend toward an increase 



Fig. 13 — -72 duct underground cable run under construction. 



in the extent to which the operations are performed by automatic 

 machinery. The general characteristics of the different types of 

 switching systems in use in the United States and their extent of 

 use are briefly discussed below. 



Magneto 



Magneto switching arrangements are used in small places and 

 scattered rural areas. They vary in size from an arrangement to 

 interconnect two or three lines up to a switchboard handling 300 to 

 400 lines. The average size of the magneto switchboards in the Bell 



