I 



CROSSBAR DIAL TELEPHONE SWITCHING SYSTEM 85 



of the vertical circuit paths. At the lower end of these strips and 

 facing the front is another projection used by the maintenance force 

 for testing purposes. The mate or movable spring of each pair is 

 individually insulated from all other springs. These springs extend 

 to the rear of the switch for wiring purposes and may be strapped 

 horizontally to the corresponding springs of adjoining vertical units 

 to extend the horizontal circuit path through the switch. 



The contacting ends of the thin movable contacting springs are 

 bifurcated to provide two flexible contacts in parallel. The con- 

 tacting surfaces on these springs as well as the mating fixed springs 

 are provided with a thin layer of palladium. The use of the double 

 precious metal contacts is an important feature of the crossbar system 

 in providing more reliable contacting surfaces. Experience has shown 

 that the chance of simultaneous failures of both contacts of a pair is 

 extremely small. The actual contacting surfaces of each pair of 

 springs consist of small bars of contact metal located at right angles 

 to each other. These bars are composed of a ribbon of nickel capped 

 with a thin layer of palladium. This crossbar arrangement of contacts 

 provides a rather large area over which the two springs can make 

 contact with each other, and thereby permits considerable tolerance 

 in the manufacture and adjustment of the contact spring assemblies 



The switch may be equipped with "off normal" contact spring 

 assemblies. When these are furnished they are associated with each 

 selecting or holding magnet and are operated like relay contacts when 

 the associated magnet operates, regardless of which crosspoint contact 

 is closed. They are used to perform circuit functions as required in 

 the. various uses of the switch. 



In the design of the switch special attention was given to the 

 problem of wiring and cabling. Figure 4 shows the wiring terminals 

 on the rear of the switch. These terminals are arranged for individual 

 wiring and also have staggered, notched projections so that the 

 terminals can be readily strapped together horizontally with bare 

 wire as shown. This is an important feature of the switch since it 

 permits a multiple of terminals to be easily soldered together and 

 reduces the wire congestion on the switch: 



The 200-point crossbar switch is 9j inches in height and 30| inches 

 in length. In addition a 100-point switch 20| inches in length is 

 provided. This switch is similar to the 200-point switch but is 

 equipped with 10 vertical units. 



