530 



THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1953 



theoretical predictions can be made on the durabiUty of new connec- 

 tions, it affords additional satisfaction to be able to show that the solder- 

 less wrapped connection is in many respects similar in structure and 

 performance to the conventional screw connection. If then this fact is 

 supported by parallel analytical work, there should be little doubt that 

 the solderless wrapped connection is a durable pressure connection. 



THE RECTANGULAR TERMINAL 



Generally speaking the terminal best suited for a wrapped connection 

 is a terminal of rectangular cross section. It is an inexpensive terminal 

 since it can be blanked from sheet stock or coined from round wire. It 

 is ideally suited for a pressure connection because the edges produce a 

 concentrated high pressure on the wire. The stress distribution in the 

 wire produced by the terminal edges is shown diagrammatically in Figs. 

 4 and 5. If the wire is wound with high tension around the rectangular 

 terminal, the terminal edges dig into the soft copper wire, crush and 

 shear the oxide on both the wire and the terminal and form a large, 

 intimate and metallically clean ''gas tight" contact area. An indication 

 of the high pressure is the crushing of the hard nickel silver terminal 

 edge by the soft copper wire. A pattern of contact areas on both wire 

 and terminal is shown in Fig. 6. Several turns of wire are required to 

 preserve the high contact force. In general it is assumed that the first 

 and last two edges around which the wire is wrapped do not contribute 

 much to the joint as contact areas. A seven-turn wrapped connection on 

 a rectangular terminal thus has six effective turns. Each turn contacts 

 four edges or a total of twenty-four contact areas for six effective turns. 



/MEDIUM TENSION 



MAXIMUM 

 TENSION "" 



TERMINAL 



MAXIMUM/ 

 COMPRESSION 



TERMINAL 



Fig. 4 — Stress distribution along 

 one-quarter turn of wire. 



Fig. 5 — Cross section through 

 terminal edge showing stress distribu- 

 tion in the wire. 



