712 



BELL SYSTEM TECHNICAL JOURNAL 



being given to arrangement of cables and use of large conductors. This 

 imposes certain limitations upon the location of equipment and may 

 involve considerable cost for copper in the larger power plants. How- 

 ever, by means of the electrolytic condensers, previously mentioned, 

 located at battery fuse panels, crosstalk on talking feeders can be re- 

 duced to very low values, the limitations on floor plan arrange- 

 ment can be largely removed and substantial savings in copper can be 

 made. 



Battery Reserve 

 In order to insure continuous telephone service in spite of failure of 

 the primary sources of power, it has been customary, as already men- 

 tioned, to provide storage battery capacity sufficient in itself to operate 



Fig. 7 — Battery room for two large panel units. 



the central office equipment for a considerable period. The amount of 

 battery reserve provided depends upon the reliability of the regular 

 outside power service and on the reserve source provided. This 

 battery reserve may range from about three net busy hours for offices 

 in large metropolitan districts to several days in small outlying offices. 

 This reserv^e in the past has been successful in preventing suspension of 

 telephone service due to failures of the power. With the greatly 

 extended plant and the increasing reliability of the public service supply 

 companies, however, the allowance of battery reserve in some cases can 



