The micro-gap switch

Alternating-current circuits that can be classed as noninductive may be broken by a switch in which the separation between the sparking contacts is extremely small. In these micro-gap switches the separation of the contacts on a 250-volt circuit is of the order of 5 thousandths of an inch, and, by the use of a back stop, is not allowed to be more than that distance. The current is interrupted, not by stretching the arc at break, but by the mutual repulsion of .electrons that enter the gap from the contacts. Oscillograms are given which show that, when the contacts in these switches begin to open at any point in a half-wave, the current breaks at the next zero point and does not restrike. If broken at zero it persists for the next halfwave. This type of switch is most suitable for the thermostatic control of electric heating systems.