Electrical switching device for thermal and overvoltage protection

A normally open, temperature-sensitive, electrical switching device, having first and second current carrying electrical leads, for completing an electrically conductive circuit between the first and second electrical leads when the temperature of the switching device exceeds a predetermined level and for providing an air gap which permits current to flow between first and second current carrying electrical leads when the voltage across said first and second electrical leads is sufficient to cause arcing across said air gap, comprising:

• a first electrically conductive electrode means including a case having a first end defining an opening into a central cavity and a second end which is closed, said first electrode means being electrically connected to said first electrical lead,
• a second electrically conductive electrode means electrically connected to said second lead,
• nonconductive means for mounting said second electrode means such that it extends into said central cavity, said nonconductive means sealing said opening into said cavity,
• a heat fusible, electrically conductive pellet positioned in said central cavity in electrical contact with said second electrode means;
• and
• insulator means, positioned between said conductive pellet and said first electrode means, for holding said pellet out of electrical contact with said first electrode means and defining an air gap therebetween of predetermined dimension,
• whereby an open electrical circuit will be maintained between said first and second electrical leads until said predetermined temperature level is reached and said fusible pellet melts, forming an electrical connection between said first and second electrode means, or until the voltage across said air gap exceeds the voltage level required for arcing thereacross.