1502 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1953 



0.4 0.5 0.6 



0.8 1.0 1.5 2 3 4 



MAXIMUM CURRENT IN ARC IN AMPERES 



7 8 9 10 



Fig. 7 — Dependence of minimum arcing current on maximum arc current. 



In the first part of this paper it was shown that contact activation by- 

 organic vapors reduces the arc initiation voltage for a fixed separation. 

 In other words, for a pair of closing contacts the arc will be initiated at 

 a wider separation and a longer arcing time is obtained. In addition, 

 activation tends to decrease the minimum arcing current. Germer , meas- 

 ured a minimum arcing current of only 0.027 to 0.037 ampere for active 

 silver. Our measurements for active palladium gave a minimum arcing 

 current of 0.1 ampere. This substantial decrease in the minimum arcing 

 current of contacts due to surface activation usually causes a further 

 increase in the arcing time. Contact activation, therefore, enhances 

 arcing between closing contacts in two ways; first, by initiating the arc 

 at wider separations, and second by maintaining the arc at much smaller 

 currents. The following results are presented to indicate the quantitative 

 significance of contact activation. A pair of ''normal" palladium contacts 

 were operated in air saturated with d-limonene at 3 cps. The contacts 

 closed a circuit consisting of a 0.5-microfarad condenser, charged to 50 

 volts, in series with a 100-ohm resistor. The transient on make was 

 observed on a cathode ray oscilloscope to determine the arcing time. The 

 arc energy Ea was calculated and the ratio EJCv {Vq — v) was plotted 

 against the number of operations. Fig. 8. The denomenator is the maxi- 

 mum arc energy, which is only attained if the arc is maintained until 

 the current reaches zero. The results indicate a rapid increase of the arc 

 energy corresponding to an increase in surface activation. When the 

 contacts become fully active, the arc energy was about two orders of 



