514 



BRLL SYSTEM TECHNICAL JOURNAL 



traffic data were then available upon which to base the design of the 

 switchboard, a general view of which is shown in Fig. 6. 



Efficient design requires that the width of a position be kept as 

 small as possible to avoid the excessive cost of a long switchboard 

 multiple. Because the smaller capacity required for this switchboard 

 did not make the vertical reach an important factor, a key-shelf 

 arrangement different from that used for the No. 1 switchboard was 

 adopted. 



Instead of placing the teletypewriter and cords on the same level 

 as in the No. 1 switchboard, the cords are placed above the 



Fig. 6— No. 3A Teletypewriter Switchboard at Pittsburgh, Pa. 



teletypewriter. This was accomplished by the use of a sloping key- 

 shelf permitting the cords to pass by the teletypewriter in the manner 

 shown by the cross-sectional view in Fig. 7. With the object of 

 keeping the vertical height of the keyshelf as small as possible, the 

 cords are located in a single horizontal row instead of in the con- 

 ventional double row. With this arrangement, the answering cord is 

 the left cord of a pair and the calling cord is the right cord. Differ- 

 entiation is obtained by using colored plug shells, black for the answer- 

 ing cord and red for the calling cord. 



An additional feature resulting from this relation of the keyshelf to 

 the teletypewriter is an arrangement whereby the position may be 



