Cathode Drop of an Arc

Abstract

By use of the method of Betz and Karrer the cathode drop of an arc has been measured for a number of electrodes, including copper, silver, iron and arc welding electrodes with and without coatings. The time for an arc to establish the cathode drop voltage measured from the time the ``last'' contact causes an appreciable voltage drop is found to be less than 40 microseconds. The cathode drop for copper is found to decrease with air pressure from 13 volts at atmospheric pressure to 8 volts at 0.1 mm of Hg pressure.