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BELL SYSTEM TECHNICAL JOURNAL 



boxes and pulse machines provide impulses for the operation of cer- 

 tain of the machine switching apparatus. 



Whenever practicable, two or more commercial power services from 

 independent generating stations are secured, either of which will keep 

 the office supplied. Where independent generating systems are not 

 available a reserve gas engine supply (Fig. 17) is installed to take 

 the place of the incoming power service, such engine also being 

 equipped for emergency operation on gasoline. 



Fig. 16— Battery Room for Two 10,000-Line Units 



All of the essential power machines and batteries are provided 

 in duplicate and are arranged to come into action automatically 

 wherever this is necessary to insure continuity of service in the event 

 of loss of power or trouble with any of the power equipment. Alarms 

 are provided to detect variations in battery voltage, blowing of fuses, 

 stopping of machines or any failure of service on all power busses 

 which feed energy to the telephone or signaling circuits. The power 

 plant is thus designed to give an uninterrupted energy supply at all 

 times even when the usual sources of power may have been tempor- 

 arily discontinued. 



