ARCING OF CONTACTS IN TELEPHONE SWITCHING CIRCUITS 1239 



Table I — Arc Initiation and Arc Termination Currents 

 Palladium Contacts in Air* 



Arc Initiation Cur- 

 rent 



1%: Amps. 

 Arc Termination 

 Current 

 Im'. Amps. 



0.12 0.21 0.21 0.150. 250. 19 0.230. 400. 65 0.61 '0.57 0.520. 45 



0.13 



0.16 



0.17 



0.20 



0.220.24 



0.24 



0.420.500.520.53 



0.58 



0.59 



* Both numbers given in one column were obtained from the same transient. 



spective records of the voltage change at the main condenser. Fig. 6 (A) 

 corresponds to the case where the multiple discharge period was short 

 and lead to a steady arc. During this arc the main condenser voltage 

 dropped from point 1 to point 2 when the arc was arrested. This was fol- 

 lowed by striking a second arc in the opposite direction which lasted 

 until point 3. Line 3-4 represented the recharging of the main condenser 

 from the power supply circuit. Superimposed on the same figure is the 

 trace 1-2-3-5 corresponding to a closure at the contact instead of an 

 open circuit. While line 1-2-3 shows two consecutive arcs, it is generally 

 possible to obtain any number of such arcs. An even number of arcs 

 will result in a positive residual voltage at the main condenser, Fig. 6 (A) 

 while an odd number of arcs will result in a negative residual voltage at 

 the main condenser. Fig. 6 (B). 



Figs. 7 (A) and 7 (B) correspond to the case when the multiple dis- 

 charges did not lead to a steady arc due to insufficient current build-up. 

 The multiple discharges caused a voltage drop 1-2 across the main 

 condenser followed by an open circuit and recharging, 2-3. 



Discharge of the Local Circuitry at the Contact 



Fig. 8 (a) represents a plausible representation of the local circuitry 

 at the contact. When the conditions between the contacts are favorable 



7.4 7.4 



TIME, T, IN SECONDS X 10"® 



Fig. 5 — Circuit current transients without a steady arc. 



