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THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1951 



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Fig. 28A — Another auxiliary vault installation of exchange area loading. One end of 

 vault. At time of photograph, 33 cases containing a total of 11,241 coils were installed 

 in this vault. A majority of the cases appear both in this view and in the view of Fig. 

 28B. 25 cases have 303, 304 or 305-coil complements, each of the other 8 cases have 455 

 or 456 coils. The total complement comprises 2 cast iron cases, 17 rectangular welded 

 steel cases, and 14 tubular thin steel cases. The individual coil codes are 612, 613, 614, 

 622, 623, and 643. The coil inductances are: 88 mh, 70%; 135, 27% and 175 mh, 2.7%. 

 35% of coils have permalloy cores; the others have molybdenum-permalloy cores. 57% 

 of coils have formex insulated windings. 



Many of the individual designs were relatively tall, with cross sections re- 

 quiring small amounts of floor space. The recent trend in case design (1948, 



