526 



THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1953 



WHAT IS A PRESSURE CONNECTION? 



The chart Fig. 1 shows six typical pressure connections classified in 

 terms of seven requirements. In this classification the screw connection, 

 for example, meets the following requirements: large contact area, high 

 contact force, great mechanical stability, long life, easy to disconnect. 

 The space, however, which the screw connection occupies is large and 

 its cost is high. In the history of electricity it is probably the oldest and 

 best pressure connection. In the second column of the table in Fig. 1 

 is the plug connection. It is small in size, easy to disconnect, but has no 

 large contact area, no high contact force, no long life, no mechanical 

 stabiUty and is not low in cost. 



As will be shown later the solderless wrapped connection in Colimin 6 

 of Fig. 1 is indicated as meeting all seven requirements. Its main advan- 

 tage over the screw connection is that it is low in cost and small in size. 



CONTACT AREA 



The effective contact area relative to the cross sectional area of the 

 wire is of great importance since it controls the resistance of the con- 

 nection. It must remain uniform in size, metallically bright and not be 

 affected by temperature changes, vibration and handling. 



Contact area is not easily defined. For example two flat metal sur- 

 faces having an area of one square centimeter each and brought into 

 contact do not necessarily have a contact area of one square centi- 

 meter. If the force holding them together is small, only the high spots 



REQUIREMENTS 



1. LARGE CONTACT AREA 



2. HIGH CONTACT FORCE 



3. LONG LIFE 



4. SMALL SIZE 



5. MECHANICALLY STABLE 



6. EASILY DISCONNECTED 



7. LOW COST 



FAHNESTOCK 

 CLIP 



PLUG 



SOLDERLESS 

 SCREW WRAPPED 



\^ \^ \^ v^ 



w' %^ »^ v^ 



%^ V-- v^ V- 



^ »^ %^ 



Fig. 1 — Classification of pressure connections. 



