534 



THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1953 



Fig. 9 shows in diagrammatic form how the stored energy in a screw 

 connection and a solderless wrapped connection compare. A typical 

 solderless wrapped connection — seven turns of 20-mil copper wire 

 wound with 1300 grams applied force on a 0.0148" x 0.062" nickel silver 

 terminal — has approximately 3 mil pounds of stored energy E. (2.4 

 mil pounds are stored in the terminal and 0.6 mil pounds in the wire). 

 The screw connection — No. 4-40 screw (0.112") tensioned to 135 lbs 

 on 20-mil copper wire — has approximately 2.7 mil pounds of stored 

 energy E. (Approximately half in the screw and half in the wire). In 

 the screw connection the energy is about equally divided between the 

 screw and the wire whereas in the solderless wrapped connection a 

 larger part of the energy is stored in the terminal. This is advantageous 

 since the hard materials of which terminals are generally made have 

 less cold flow than copper. In a solderless wrapped connection, if the 



NO. 4-40 (0.112") BRASS SCREW 



N0.24GA (0.020") COPPER WIRE 



CONTACT FORCE 135 LBS 



(a) SCREW CONNECTION 



0.0148" X 0.062" NICKEL SILVER TERMINAL 



7 TURNS N0.24GA (0.020") COPPER WIRE (1300GR AF) 



CONTACT FORCE 90 LBS (24 CORNERS) 



(b) SOLDERLESS WRAPPED CONNECTION 

 2.4 



SCREW 



0.6 



WIRE 



TENSION COMPRESSION 



18,750 PSI 18,250 PSI 



E = 1,4 + 1.3 =2.7 



TORSION AND TENSION 



COMPRESSION 8500 PSI 



E = 2.4 + 0.6 = 3 



( C I TOTAL ENERGY E (IN lO'^ INCH LBS) 



Fig. 9 — Elastic energy stored in screw connection and in solderless wrapped 

 connection. 



