Abstract: A thermal switch having a tubular metal casing within which a fusible pellet normally holds an axially slidable electrical contact disk in contact with an electrical lead. The body of the electrical lead extends through a ceramic bushing and out of the casing for electrical connection, and it is formed with at least one radially-extending relief lying within the bore of the ceramic bushing. A sealing resin within the bore of the ceramic bushing and around the lead retains the lead in the bushing both in normal use and after the fusible pellet has melted and the electrical connection is broken.