18 



BELL SYSTEM TECHNICAL JOURNAL 



lengths of pulp insulated cables which so far as was known differed 

 only as regards the lack of symmetry of the insulation. 



Mutual Capacitance Vs. 



Direct Capacitance to Ground 



Direct Capacitance to Mate 

 Average Value in m.m.f. 



The alternating current mutual conductance follows the trend of the 

 capacitance, resulting in the ratio of conductance to capacitance at a 

 frequency of 900 cycles per second being somewhat higher than the 

 standard ribbon paper cable, but not of a magnitude such as to intro- 

 duce any serious transmission loss for these fine gauge circuits. The 

 direct current insulation resistance is of the same order as that of 

 strip paper cables. 



The dielectric strength of the insulation is ample, being somewhat 

 higher on the average than that of similar strip paper cables. A 

 rather extensive series of mechanical tests comparing pulp and ribbon 

 types of insulated cable under controlled conditions simulating those 

 met with in actual installation, showed that the pulp insulated cables 

 remained superior to the ribbon cables as regards dielectric strength 

 but that under extreme loads they would not withstand quite as much 

 stretch as the ribbon insulated cable without mechanical damage to 

 the insulation. 



Installation Features 



No new features are involved in installing pulp insulated cable 

 except in the splicing of the conductors after the lengths as supplied 

 from the factory have been placed in position in the plant. This 

 operation, however, is a considerable factor in the total time of the 

 installation procedure because in a not unusual run of a mile of an 

 1818 pair cable, there may be as many as 40,000 joints to be made in- 

 volving the stripping of twice that number of ends of insulated wire 

 preparatory to joining the copper conductors. 



Immediately upon removing the lead sheath from the ends of the 

 cables thus exposing the dry insulation to the atmosphere, absorption 

 of moisture rapidly takes place. It is customary, therefore, to boil 

 out the ends of cable with paraffin wax before starting the splicing 

 operation. With strip insulation this wax also aids in preventing the 



