MACHINE SWITCHING TELEPHONE SYSTEM 



73 



driven by the same motor which insures continuous service in case 

 of motor failure. 



The main power requirement is for direct current at about 24 and 

 48 volts which is furnished from motor generator sets (Fig. 15) of 

 special construction to reduce noise, converting the commercial 

 alternating or direct power current into current which is regulated 

 as to voltage and is free from variations which would cause noise in 

 the telephone circuits. 



Fig. 15 — Power Machine and Control Equipment for Two 10,000-Line Units 



Storage batteries (Fig. 16) floating across the current supply bus- 

 bars insure regulation. In addition to stabilizing the voltage and 

 reducing noise interference from the machines and between tele- 

 phone circuits, the batteries perform the important function of keep- 

 ing the exchange in operation during interruptions to the commercial 

 power service. Small motor generators furnish current for ringing 

 subscribers' bells and drive commutators supplying various tones and 

 signals. Batteries or machines supply current for operating coin 



