170 BELL SYSTEM TECHNICAL JOURNAL 



supplied by tlie high voltage coiulenser where it is employed or by 

 the air separation where the coupling wires are employed, is dis- 

 regarded, since this insulation ma\- fail, thereby apiiKing the power 

 line voltage to the line terminals of the coupling circuit shown in 



I — nnsw^ 



I — npppr^ 



/T?RJF|— iihn 



—■\H 



Fig. 18 — St'hematic of Wire Coupling Circuit 



Fig. 21. The circuit shown in this figure is the same both for con- 

 denser and for wire coupling instiiUations. The first element of 

 protection is the horn gap, which is mounted outside of the building 

 and serves to limit the voltage to ground which tlie drop wire fuse, 



CfiCPlEP FPECUENCY IN KILOCYCLES 



Fig. 19 — Charaitt-r of Resonant Peaks secured with Wire Coupling 



constituting the second element of protection, will ha\'e to break. 

 This fuse consists of an element inside of a jjorcelain tube the ends 

 of which are closed by lead caps. This fuse is about 5 inches long 

 and } 2 i'leh in diameter and is supported by the wire itself. When it 



