536 



THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1953 



Fig. 11 — Twist of rectangular terminal (100 turns of wire). 



the terminal would be compressed at the edges but the terminal would 

 not twist. The terminal twist in the wrapped connection is therefore due 

 to the fact that the terminal is surrounded by a helix and not by hoops. 

 Figs. 10(a) and 10(b) show that a left-hand helix produces a right-hand 

 twist in the terminal. As will be shown later, this visible deformation of 

 the terminal is being used to determine the tension in the wire. The 

 twist in the terminal of a wrapped connection with many turns can 

 readily be seen in Fig. 11. For example an initial twist of 46° is produced 

 in a nickel silver terminal 0.0148" X 0.062" wrapped with 100 turns of 

 No. 24 (0.020" dia.) copper wire with an applied force of 1300 grams. 

 One way to visualize the behavior of the wire and the terminal when 

 wrapped under tension, exposed to time and heat and then unwrapped, 

 is to represent the wire and the terminal by linear springs. This is shown 

 schematically in Fig. 12. Position 1 represents both wire and terminal 

 before wrapping. Position 2 represents the wire wrapped on the ter- 

 minal. Position 3 is the same as Position 2 except that the wrapped 

 terminal has been exposed at room temperature (20°C) for eight days. 

 This causes the terminal twist to relax from 46° to 39°. Positions 2 and 

 3 are analogous to the wire under tension and the terminal under tor- 



ROOM TEMPERATURE 

 V/////////////////////////////////. 



WIRE 

 TINNED COPPER 

 24 GA (0.020") 



100 TURNS 

 APPLIED FORCE 

 OF 1300 GRAMS 



TERMINAL SET 



TERMINAL 

 NICKEL SILVER 

 0.0148" X 0.062" 



TENSIONED 



P0S.4 

 RELEASED 



V/////////////////////////A 



PCS. 5 PCS. 6 POS.7 



TENSIONED AFTER RELEASED 



HEAT (AFTER HEAT) 



Fig. 12 — Energy in unheated connection proportional to 30°. Energy in heated 

 connection proportional to 14°. 



