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BELL SYSTEM TECHNICAL JOURNAL 



wires 1 and 2 comprising one pair, 3 and 4 another, etc. The character- 

 istics of the pairs are of primary interest. Phantom circuits, which are 

 derived from two pairs or side circuits, will be discussed later. The 

 two wires of each pole pair (that is, a pair which bestrides the pole) are 

 about 18 in. apart, and those of each non-pole pair 12 in. apart. 



There has recently come into vogue a different arrangement of wires 

 which is designed to reduce the coupling between circuits and thus per- 

 mit a maximum use of carrier facilities. This arrangement is por- 

 trayed in Fig. 2. In this newer configuration the separation between 

 the wires of each non-pole pair is reduced to 8 in., and the horizontal 

 separation between pairs is widened to 16 in. 



Fig. 2 — Configuration of an open-wire line with 8-in. non-pole pairs. 



The ordinary spacing between poles on open-wire toll lines is 132 ft., 

 corresponding to a total of 40 poles per mile. \\'here additional 

 strength is required, the number of poles per mile may be as high as 50, 

 while outside of the heavy sleet area it may be as low as 30. 



The types of insulators employed on open-wire lines will be dis- 

 cussed under the heading of leakage conductance. 



Two methods of transposing the wires are in current use. In the 

 older of these, which is illustrated in Fig. 3, the wires are brought at the 

 transposition pole to a "drop bracket." The transposition is accom- 

 plished over a total distance of two spans by gradually rotating the 

 plane of the wires through 180 deg. It will be seen that the wire con- 

 figuration is abnormal throughout the two spans. In the newer 

 method, the wires are crossed practically at a point. This may be 

 done by means of two brackets known as "break irons," as illustrated 

 in Fig. 4, or by means of a single bracket. The "point" transpositions 



