738 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1951 



coils. These mixtures usually comprised combinations of coils for four-wire 

 long-haul circuits with one or two types of coils for short-haul or medium- 

 haul two-wire circuits. When this practice of mixed potting complements 

 started, it was customary to use different stub cables for each different 

 potting-mixture, even when the same total number of loading units were 

 involved. In these stub cables, each of the different types of loading units 

 had its own individual color-code identification. In the new set-up, the rela- 

 tively simple color-code counting-scheme provided full flexibility for all 

 desirable combinations of different types of loading units. 



Loading units of a given type made use of terminal quads having con- 

 tiguous numbers in the quad counting-scheme. In mixtures involving two 

 types of loading units, for example PIB and PUB units, the units having the 

 lower-number component in their code-designation used the low-numbered 

 terminal quads, and the units having the higher code-number used the high- 

 numbered terminal quads. In mixtures involving three different types of 

 loading units, the units having the intermediate code-number in their code 

 designation used a contiguous group of terminals which were intermediate 

 in position between the low-numbered quads and the high-numbered quads 

 which were respectively associated with the loading units having the lowest 

 and the highest code numbers. These procedures were followed in each of 

 the two segregated groups of opposite-direction loading units previously 

 mentioned. 



Quadded Stub Cables for Non-Phantom Coils: During the 1930's, the 

 practice of using quadded stub cables for cases potting non-phantom type 

 exchange area and program circuit loading coils was started. One pair of 

 each terminal quad was connected to the IN terminals of a coil, and the 

 associated pair was connected to the OUT terminals of the same coil. 

 Previously, the IN and OUT terminals had been grouped in different unit 

 cables. The close association of IN and OUT terminals in the new quadded 

 stub cables reduced the factory testing-time, and simplified the preparatory 

 phases of the field splicing of the stub cables to the main cables. Other 

 subsequent improvements included the use of paper-pulp insulation on the 

 stub cable conductors, in place of textile insulation. By this time it had 

 become a common practice to terminate the coil windings on terminal clips 

 mounted in close proximity to the coils. The inner ends of the stub cable 

 conductors were soldered directly to these clips. 



Stub Cable Conductor Sizes: Since the case stub cables are extensions of the 

 main cables, transmission considerations have generally led to the use of 

 about the same sizes of conductors. However, notable exceptions to this 

 rule have been accepted in situations where conformation to the rule would 

 have made the stub cable unduly expensive, or unduly large and difficult to 



