594 THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1953 



Table I — Thickness of Material which Corrodes in Forty 



Years 



Zinc 0.00023" 



Copper 0.000105'' 



Tin Negligible 



copper and zinc. There are very few data available on tin but its cor- 

 rosion should be less than either copper or zinc. From the data presented 

 the depth of metal which will corrode during a forty-year period in a 

 central office for several metals is estimated* to be as shown in Table I. 



Samples of copper bus-bar taken from telephone exchanges where 

 they have been exposed for periods up to forty years show that the 

 tarnish is primarily CU2O and the actual rate of corrosion may be ap- 

 preciably less than that estimated by the above figures. 



Thus the depth of metal corroded is small enough to neglect when the 

 metals are subject to indoor atmospheric exposure. When dissimilar 

 metals are joined in a connection there is the possibility of electrolytic 

 corrosion in addition to atmospheric corrosion. The particular metals 

 involved here, however, are relatively close to each other in the electro- 

 motive force series of metals so that it is expected that this effect will 

 be negUgible especially as there is no condensation on these connections. 



It is therefore expected that the most important factor in the aging 

 of these connections is the relaxation of stresses internal to the wire and 

 the terminal rather than corrosion. The test procedures and results in 

 the following sections reflect that view. 



development test procedure — electrical requirements 



General Requirements 1 through 4 are considered together. A set of 

 tests has been designed to evaluate the degree to which these require- 

 ments can be met. 



Since the tests which have been devised are destructive it is necessary 

 to check connections in production on a sampling basis. 



In determining whether a connection meets the General Require- 

 ments 1 through 4, Test Procedure I as follows was devised. 



Test Procedure I for Solderless Wrapped Connections 



1. Check connection for insulating barrier film between wire and 

 terminal. 



2. Measure the variation of the resistance of connection while pro- 

 ducing movement between the terminal and connecting wire. 



* Unpublished memoranda, D. H. Gleason, Bell Telephone Laboratories. 



