352 



ELEMENTS OF ELECTRICAL ENGINEERING. 



is not thoroughly insulated from the telephone line, more or less 

 current will leak across from one to the other. 



What is here said of the effect of an alternating-current line 

 upon a telephone line applies also to the effect of one alternating- 

 current transmission line upon an adjacent alternating-current 



X 



X 



X 



Fig. 300. 



transmission line. These effects are especially troublesome, 

 however, in telephone lines which are adjacent to alternating-cur- 

 rent transmission lines, and they may be obviated * by thorough 

 insulation, and by what is called transposition of wires of one of 

 the lines. The essential features of transposition are shown in 

 Fig. 300. At frequent intervals along the line the two wires of 

 the line cross over or change places. Fig. 301 shows the method 



fop view 



side view 



A B 



Fig. 301. 



of transposing telephone lines. Three cross-arms are attached to 

 the pole at which the transposition is to be made, and upon the 

 middle arm a " two story" insulator is placed so as to bring one 

 of the wires above the other as indicated in the figure. 



* See a paper by P. M. Lincoln, Transactions of the American Institute of Elec- 

 trical Engineers , Vol. 21, pages 245 to 251, and a paper by F. F. Fowle, Trans- 

 actions of the American Institute of Electrical Engineer s^ Vol. 23, pages 659 to 

 689. The important part of this latter paper is included in pages 674 to 687. 



