Abstract: An arc suppressor for a sidactor type protective device wherein the sidactor type protective device comprises a sidactor body portion, two end line terminals, a central ground terminal, and a fail-safe mechanism mounted upon the terminals of the sidactor in order to shunt or short-circuit the sidactor under overload conditions. The arc suppressor comprises a housing or cap tightly enveloping or encasing the sidactor body portion so as to enhance the strength thereof and thereby maintain the structural integrity of the body portion by effectively preventing any cracking thereof under overload conditions. The prevention of the cracking of the sidactor body, in turn, insures that any plasma gas or cloud generated within the sidactor body under high-voltage overload conditions is contained within the sidactor body and does not escape therefrom so as to otherwise present an environment conductive to arcing between the terminals of the sidactor.