TOLL SWITCHBOARD NO. 3 25 



must be suitable to work with any toll line terminating at the switch- 

 board and consequently with the circuit arrangement used in toll 

 switchboard No. 1, the ringing relay in all the toll cord circuits must be 

 maintained to operate in connection with the longest as well as the 

 shortest line circuit. In the case of the No. 3 toll switchboard, how- 

 ever, the ringing relay is individual to the line and consequently may 

 be adjusted to meet the operating conditions of that line. Long lines 

 with severe ringing conditions require the relay to have a sensitive 

 adjustment while short lines with easy ringing conditions permit a 

 less sensitive relay adjustment to be used which is more easily main- 

 tained. 



Easily Adaptable to Machine Switching Methods 



The introduction of machine switching requires provision for dialing 

 on the trunks and may in the future require the same feature for dialing 

 over toll lines. Such provision in the boards previously employed 

 requires the addition of the necessary keys and relays on a "per cord" 

 basis, whereas with the No. 3 board the equipment can be placed in 

 the positional circuit, without any change in the cord circuit. This 

 results in a great economy in apparatus and makes a change to a dialing 

 basis rather simple. 



Summary 



It is interesting to note in conclusion that heretofore an increase in 

 cord circuit apparatus has necessarily followed the development of 

 new and improved switchboard systems and the extension of the area 

 of long distance communication. For example, the magneto cord 

 with a single drop bridged across the circuit sufficed in the early days 

 of small magneto boards. The advent of the common battery multiple 

 switchboard brought the necessity for extending switchhook super- 

 vision to the toll operator, and resulted in the condenser-type cord 

 consisting of 5 relays, now largely abandoned because of the relatively 

 large transmission loss introduced by it. The high-efficiency cord 

 consisting of 8 relays resulted from the demand for a cord having a 

 minimum transmission loss, and- additional complications have re- 

 sulted in the requirement for dialing in machine switching areas, each 

 improvement, of course, increasing the number of relays in the cord 

 circuit. The No. 3 system, on the other hand, makes possible by the 

 transfer of apparatus to the line and switching trunk and by the use 

 of common positional equipment the relatively simple toll cord shown 

 in Fig. 2 in which the individual apparatus is limited to two keys and one 



