Thermal switch

A thermal switch comprising:

• a tubular, electrically and thermally conductive metal casing,
• a first electrically conductive lead joined to and extending from one end of said metal casing to seal off said one end and make electrical connection to said casing,
• an insulative ceramic bushing at the opposite end of said casing, said bushing sealing said opposite end of said casing and having its bore coaxial with said casing,
• a normally solid, fusible pellet within said casing adjacent to said one end,
• a second electrically conductive lead having a generally cylindrical body extending through the bore of said ceramic bushing and out of said casing to permit electrical connection thereto, and having a head abutting the end of said ceramic bushing within said casing, said body of said second lead being formed with at least one radially-extending relief lying within the bore of said ceramic bushing, said relief extending around less than the entire circumference of said body, said second lead being retained in said ceramic bushing by a sealing resin within the bore of said bushing around the body of said second lead,
• an electrically conductive disk positioned within said casing between said fusible pellet and said head of said second lead coaxial with said casing, slidable axially within said casing and making electrical contact with the wall of said casing, and
• resilient means urging said disk into electrical contact with the head of said second lead when said fusible pellet is solid and away therefrom upon melting of said fusible pellet.