982 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1952 



The degree of improvement obtained by the use of cellulose acetate 

 over the materials formerly used is shown in Fig. 3. This is the result 

 of an accelerated corrosion test adopted as a means of obtaining data 

 on proposed constructions, using as a basis for comparison, the perform- 

 ance, in this test, of the earlier spool wound construction. The latter had 

 given satisfactory service in the field, only occasional failures occurring 

 under the most severe circuit and atmospheric conditions. This test is 

 made with double or triple wound coils since these represent the most 



SPOOL WOUND COIL 



CELLULOSE ACETATE FILLED COIL 



(former insulation) 



(present insulation) 



c^d l^ @' 



!>k1^3d® 



<m q\^^ 



COIL COVER 

 WAXED VARNISHED KRAFT PAPER 

 INTERWINDING 

 CORE INSULATION 



CELLULOSE ACETATE 

 COIL COVER 

 INTERLEAVING 

 INTERWINDING 

 CORE INSULATION 



50 



28 



35 



7 14 21 



DAYS ON TEST 

 AT 90°/o RELATIVE HUMIDITY AND 85° F 



7 14 21 28 35 



DAYS ON TEST 



AT 90°/o RELATIVE HUMIDITY AND 85° F 



TESTING CIRCUIT 

 CONTACT SPRING 



OUTER WINDING ^^MWM~^ 1 + 



INTERWINDING INSULATION— »- i ■ — ^^ 



INNER WINDING "''lyMMW^' ^ 



CORE INSULATION *" ' 



CORE 



Fig. 3 — Corrosion tests on relay windings. 



