TOLL SWITCHBOARD NO. 3 



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make a busy test or use the cord for a terminating or a through con- 

 nection. This cord is shown in Fig. 1. 



Fig. 1 — -High impedance toll cord for toll switchboard No. 1 



In the No. 3 switchboard the ringing relay and the direct-current 

 supervisory relay, which were formerly connected across the tip and 

 ring conductors of the cord circuit, have been moved from the cord to 

 the line and switching trunk, respectively, and the cord circuit has been 

 simplified as is illustrated in Fig. 2. In this board the line and trunk 



To Positional CKt. 



Fig. 2 — Toll cord for toll switchboard No. 3 



signals are transferred to the cord over the sleeve circuits. This is 

 accomplished by using a nominal sleeve resistance of 1,800 ohms for 

 the line and trunk circuits and connecting the lamps in the sleeves of the 

 cord. Under these conditions there is not sufficient current flowing in 

 the sleeve to light the lamp, but when a ringing signal is received over a 

 line and a cord is associated with that line or when a receiver-on-the- 



