732 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1951 



in shape, designed and installed so that the axis of the cylinder is in line 

 with the axis of the submarine cable. A stub cable extends from each end, 

 one having the IN leads to the coils, and the other the OUT leads. (Refer 

 to Fig. 24, page 727.) 



Potting Complement Sizes 



Usually, the initial traffic requirements and estimated rate of traffic growth 

 are the most important factors in determining the potting complement sizes 

 for particular projects. Frequently the initial loading complement is greater 

 than subsequent complements. In some situations, two or more cases may 

 be installed at the same time, because of the case-design size limitations. 



Non-Phantom Coils: In the early loading applications of non-phantom 

 coils, the most common potting complements were of the order of about 50 

 coils. The maximum complements prior to the development of inexpensive 

 loading for 22 ga. exchange cables ranged up to 98 coils. Complements of 

 200 and 300 coils became quite common with the Nos. 601 and 602 coils. 

 With the introduction of the No. 612 (permalloy-core) coils, complements of 

 450 and 600 coils became common, and occasionally a 900-coil complement 

 was used. The maximum complements of the much smaller molybdenum- 

 permalloy core coils have been held to about 450 coils. The foregoing is an 

 interesting manifestation of the stubborn limits upon case-design cost-reduc- 

 tion that come into play as the coils become smaller and smaller. The labor- 

 cost component is dominant and little saving in materials can be achieved. 

 In consequence, it is frequently preferable to use two medium-size comple- 

 ments, rather than one over-size complement having the same total number 

 of coils, especially if the second complement can be deferred for some time. 



Side and Phantom Coils: In the early applications of loading to quadded 

 19 and 16 ga. toll cables, the side circuit coils and the phantom coils were 

 some times potted in separate cases. In such applications, the side circuit 

 coil complements ranged up to 98 coils, and the phantom coil complements 

 ranged up to 48 coils, but the average-size complements were substantially 

 smaller. Soon it became the common practice to pot associated side circuit 

 and phantom circuit coils together in the same case, and in such instances 

 loading complements for 24 cable quads were common. To help meet the 

 increasing demand for toll cable loading in the early 1920's, maximum com- 

 plements for loading 36 cable quads became available. When the phantom 

 coils were reduced to side circuit coil-size (1923), the maximum potting com- 

 plement was increased to 45 loading units. The large coil-size reduction 

 that resulted from the use of compressed permalloy-powder cores made 

 practicable during the late 1920's and early 1930's a further, very substan- 

 tial, increase in the range of standard potting complements covering up to 



