TELEPHONE EQUIPMENT FOR LONG CABLE CIRCUITS 123 



In general, all toll line conductors are brought into a central office, 

 from the outside, through a cable and first appear at a rack called a 

 "distributing frame" where they are soldered to exposed terminal 

 lugs so that they may be reached for the purpose of connecting them 

 to apparatus within the office. This arrangement is well suited to 

 the permanent connections but is not intended to permit frequent 

 changes or the ready removal of the apparatus for line testing. 



The necessity for rearranging the connections between the ap- 

 paratus and the lines in cases of line trouble makes it desirable at 

 times to be able to make such changes quickly, and the means which 

 have been provided for this purpose are located at the "test board." 

 Here both the line conductors and the apparatus units are wired to 

 "jacks" which are arranged to permit the transfer of the normal 

 connections by the insertion of plugs wired to flexible cords. A 

 temporary connection made in this manner through a conducting 

 cord wired to two plugs is called a "patch." The apparatus for de- 

 termining the location of line trouble is also located at the test board 

 and is wired to cords and plugs so that it may be connected to any 

 line in the office readily, upon the occurrence of line trouble, without 

 necessitating changes in soldered connections. 



The test boards used for the open-wire plant have been designed 

 to take care of 40 to 80 line conductors in one position, that is, in a 

 board three feet long. The amount of testing and patching work 

 required on open-wire lines has been such as to make this a con- 

 venient number of circuits to handle within this space. In cable 

 installations, however, the amount of testing and patching per line 

 conductor is less, while the number of circuits in such an office is much 

 greater. Consequently, in cable offices it is possible to concentrate a 

 larger number of wires within a given test board space. This is 

 desirable from the standpoint of economy in space as well as from that 

 of convenience in operation. 



One of the first steps considered in the development of efficient 

 test board equipment for cable installations has been the reduction 

 of the number of jacks per circuit. In open-wire installations it 

 has been the practice to equip each line circuit and each equipment 

 unit, such as a composite set or phantom coil, with a full complement 

 of jacks suited to provide the maximum degree of flexibility in "patch- 

 ing," thus permitting the ready interchanging of individual equip- 

 ment units, lines and drop circuits. In cable installations, where 

 the circuits are more likely to be uniformly equipped with the same 

 types of associated apparatus and where the line troubles are less 

 frequent, it is expected to be possible to eliminate certain of the jacks, 



