POLE-LINE CONSTRUCTION 



59 



Fig. 19 Tripod line supports 



Section 57 Line Construction 

 1 LINE MATERIALS 



Iron wire is divided into three grades: Extra Best Best, Best Best, and Steel. 

 The Extra Best Best (E.B.B.) wire possesses the highest conductivity, but the lowest 

 tensile strength. It is designed for use on the main lines of telegraph companies, and 

 by telephone companies where a wire of high conductivity combined with strength and 

 toughness is required. The steel wire is made from a special grade of material. It 

 is the lowest in conductivity but highest in tensile strength. The Best Best (B.B.) 

 wire, which possesses intermediate qualities, is more generally used than the others on 

 medium distance circuits by telephone companies and for railway work. 



The following table gives the physical characteristics of these three grades of 

 wire : 



TABLE C PROPERTIES OF DOUBLE GALVANIZED TELEGRAPH AND TELEPHONE 



WIRE 1 



Summary of tests bv John A. Roebling's Sons Co. 



