1236 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER, 1953 



defined as the largest inductance for a given circuit above which a 

 steady arc cannot be obtained and the limiting voltage is defined as the 

 lowest voltage for a given circuit below which a steady arc cannot be 

 obtained: 



(L)u»it=J-(^'J (6a) 



/t\1/2 



(Fo-^)Limit=27,-(^y (5b) 



The assumption made that all charging processes are much longer in 

 time than the discharging times, imposes a Hmitation on the appUca- 

 bility of the above relations. Equation 4c can show that the minimum 

 charging time is (2/o))a'^. The accuracy of the above relations is better 

 the larger this time is compared to the discharge time of the local contact 

 capacitance. Assuming distributed characteristics for the local and rela- 

 tively small contact circuitry* the discharge time is 2{£c)^'^. The limitation 

 involved, therefore, is that (2/o})a'^ must be greater than 2{icf^'^ or 

 L/C > lie. In other words, the impedance of the main circuit must be 

 greater than the impedance of the local circuit at the contact. 



MEASUREMENTS 



All the measurements presented were obtained from an inductive 

 type circuit, C-L-Contact. The main circuit, Fig. 3, consisted of a con- 

 denser C in series with a honeycomb inductance which is connected by 

 a short lead, about 2 cms, to a pair of clean palladium contacts operating 

 in laboratory air. The contacts were mounted on a cantilever bar arrange- 

 ment, described by Pearson^ which allows fine adjustments of the sepa- 

 ration between the contacts as well as slow motion of the contacts to 

 avoid physical closure before the end of a transient. 



Three sets of measurements were made. 



(1) Contacts voltage measurements: the transients obtained usually 

 needed some correc;tion to compensate for the effects of the measuring 

 OBcilloscope circuit. None of these measurements are presented in this 

 paper. It may be mentioned, however, that they indicated the existence 

 of rapid discharges at the contacts preceding the estabUshment of the 

 steady arc. 



(2) Circuit current measurements. Fig. 3 (a): these were made by 



1 * ^.'L M. J***"®! »J-pti()ri of this paper, measurements were shown to indicate the 

 plaiwibihty of this aaaumption. 



• G. L. Pearson, Phye. Rev. 66, p. 471, 1939. 



