442 



THE BELL SYSTEM TECHNICAL JOURNAL, APRIL 1951 



Terminal Temperature Control Equipment 



Due to the compactness of assembly achieved with the cubic method of 

 mounting there remains very httle free space for natural or convective cool- 

 ing, and excessive concentration of heat may be expected. For the N-1 

 carrier terminals it was found necessary in high temperature areas to pro- 

 vide forced air cooling. Although the major power dissipation occurs in 

 the vacuum tubes, which are mounted on the face of the units, consider- 

 able heat from this source is conducted through to the inside of the units. 



'Tt 





Fig. 18 — An exploded view of the expander and signaling subassembly ready lor Llic 

 final assembly operation. This shows the extent to which prewiring of small assemblies 

 is used. 



With a power input of approximately 400 watts per terminal serious damage 

 to some of the apparatus might result if forced cooUng were not provided 

 in those offices where summer temperatures are high. With forced cooling 

 the maximum temperature rise is reduced to a limit well within the capabili- 

 ties of the apparatus used. 



The temperature control equipment consists of a centrifugal blower driven 

 by a iV HP 115 volt a-c motor which circulates air through ducts to the 

 equipment. The motor and blower are mounted at the bottom of each relay 

 rack with flexible connections to rectangular aluminum ducts extending up 



