TREATMENT FOR TEXTILE INSULATION 229 



for use in toll equipment where the best electrical characteristics ob- 

 tainable are needed. 



The improved electrical characteristics of cellulose acetate treated 

 insulation also make possible the elimination of enamel in a large 

 amount of wire and cable where it has formerly been required to pre- 

 vent excessive current leakage under conditions of high humidity. 

 This is of economic importance because of the difficulty of removing 

 the enamel preparatory to soldering the wire to terminals, and the 

 precautions necessary to prevent trouble from faulty soldered connec- 

 tions, which increase considerably the cost of installation and main- 

 tenance of apparatus. 



In distributing frame wire the use of cellulose acetate treated insu- 

 lation has been found to be particularly advantageous. This type of 

 wiring cannot be installed permanently in cabled form, as is the prac- 

 tice with practically all other types, because of controlling equipment 

 and service conditions, and in order to guard against fire hazard from 

 a large mass of loose wiring, the insulated conductor has, heretofore, 

 been covered with a cotton braid impregnated with flameproofing salts. 

 These salts, because of their hygroscopic and electrolytic nature, have 

 a deleterious effect on the electrical characteristics of the insulation 

 under humid conditions and introduce the danger of excessive leakage 

 and corrosion, particularly near terminals. Exhaustive tests have 

 proved that cellulose acetate treated insulation, without the addition 

 of flameproofing salts, will be as satisfactory as the old type with 

 respect to safety, and the elimination of salts has made it possible to 

 design a wire which is greatly superior to the old type electrically, 

 considerably less expensive to manufacture and smaller in size. 



Another ad\antage in cellulose acetate treatment is its effect in 

 preventing unwrapping and fraying of the textile at terminals. With 

 the old standard wires, fraying is prevented by impregnating the insu- 

 lation near the ends with wax. This wax treatment is undesirable in 

 that it adds to the flammability of the insulation, tends to obscure the 

 marking colors and collects dust. Cellulose acetate treatment binds 

 the insulation against fraying and provides a smooth glossy surface 

 which does not collect dust readily. 



These examples serve to illustrate the more important factors in 

 favor of cellulose acetate treated wire with regard to its application in 

 telephone apparatus. On the other hand, this type of wire has a 

 tendency to be somewhat stiff and springy with the result that its 

 behavior in the operations of twisting, stranding and forming into 

 cables differs considerably from that of the old untreated types. This 

 has made necessary the development of modified manufacturing and 



