SOLDERLESS WRAPPED CONNECTIONS 



PART I 



543 



Summarizing the stresses in the connection, one may therefore say 

 that in the portion of the wire where most of the elastic energy resides, 

 the stress after eight days is about 8,500 P.S.I, and at the points of con- 

 tact 29,000 P.S.I. After forty years these stresses will be approximately 

 4,000 and 13,500 P.S.I., respectively or 47 per cent of the original 

 stress. (See Fig. 19). As may be seen in the creep curves shown in Fig. 

 20, a stress of 8350 P.S.I, reaches a creep value of about 0.07 per cent 

 in three years and from then on for all practical purposes ceases to creep. 



50 



20 



1 MIN 10 MIN I HR 10 HR 1 DAY 10 DAYS 100 DAYS I YR 10 YRS lOOYRS 



TIME 



Fig. 21 — Stress relaxation in wire plotted on a logarithmic time scale. 



The effect of time and temperature on the longitudinal stress in the 

 wire can better be seen by curves plotted on a logarithmic time scale 

 (Fig. 21). The initial stress after transient relief of three days is con- 

 sidered as 100 per cent. Curve A shows that at a temperature of 57°C 

 (135°F) — which is the maximum temperature that solderless wrapped 

 connections will be subjected to — the longitudinal stress relaxes ap- 

 proximately 50 per cent in 40 years. To reach the 50 per cent value 

 at a temperature of 175°C takes approximately three hours (Curve C). 

 Curves B and C show that the relaxation in the wire is essentially the 

 same for either nickel silver or spring steel terminals. 



METHOD OF WRAPPING 



In nearly all soldered connections where a wire is to be joined to a 

 terminal the procedure is as follows: The operator takes the skinned 



