GB1143903A - Electrical switch - Google Patents

Abstract

1,143,903. Thermal switches. DANFOSS A.S. 20 March, 1967 [9 April, 1966], No. 12962/67. Heading H1N. Energization of a heating coil 9 causes contacts 1, 2 to close and after a delay to re-open. Two mutually opposed bimetal strips 5 and 6 are cantilever mounted end to end with the strip 5 being approximately twice as long as strip 6 to render contacts 1, 2 independent of ambient temperature. A thermal insulation layer 7 surrounds strip 5 so that strip 6 is rapidly heated to close the contacts 1, 2, and strip 5 is more slowly heated to provide subsequent opening of the contacts. On de-energization of coil 9, the more rapid cooling of strip 6 ensures that the contacts 1. 2 are not reclosed as strip 5 restores. The switch may be used to start a single-phase motor 11 by connecting the coil 9 in series with the running winding 12, and the contacts 1, 2 in series with a starting winding 11 to provide a short energization thereof. A plungeroperated switch (14, Fig. 2, not shown) actuated by excessive bending of strip 6 due to very high ambient temperature, may be provided as an overheat cut-out. Instead of contacts 1, 2 a snap-action switch (not described) may be actuated by the end of strip 5.