POWER PLANTS FOR TELEPHONE OFFICES 711 



The addition of these is more economical than new synchronous motor- 

 generators unless the replaced sets can be used to good advantage 

 elsewhere. 



Power Switchboards and Bus Bars 



Two recent developments are now in use which will reduce the cost 

 of control equipment and will have other advantages. Long power 

 switchboards for large power plants had to be designed in detail and 

 built individually. The use of unit control panels in power boards 

 and battery fuse panels now permits layout of a simple schematic from 

 which a power board can be assembled, using units which may be 

 stocked as demand warrants. Considerable engineering expense is 

 thus avoided since it will be unnecessary to work up the rather elabo- 

 rate detailed drawings previously required for each major installation. 



A further development of this idea is the "semi-remote control 

 system" recently adopted. With this system most of the control 

 equipment for each motor-generator set is located upon unit panels 

 mounted at the set, thus reducing the main power board to small 

 dimensions and giving increased flexibility which is particularly useful 

 in connection with additions. Overhead bus bars and conduit are 

 employed which are not installed till needed. The flexibility also aids 

 in utilizing improvements and changes in the art occurring between the 

 initial equipment installation and the additions made from time to 

 time as the growth of the load requires. 



From a production basis it is anticipated that this unit panel design 

 will be easier to manufacture and to stock and that it will also be 

 simpler to install than the earlier arrangements. 



Complete Power Unit Assemblies for Small Applications 

 Where small amounts of power are required, the provision of storage 

 batteries and associated charging equipment has been relatively high 

 in cost of material and of installation. An appreciable cost reduction 

 has been secured by the design of small power plant units complete 

 with batteries mounted in cabinets and assembled with associated 

 charging or floating equipment. 



Crosstalk Reduction 

 In a common battery telephone office all subscribers are furnished 

 with power from a single central office storage battery. There is a 

 tendency toward "crosstalk," that is, mixing of conversations, so that 

 fragments from one conversation might be overheard in another. This 

 tendency is limited by so designing the battery and wiring common 

 to all circuits that it will have very low impedance, particular attention 

 46 



