GB696269A - An improved thermally-operated electric switch - Google Patents

Abstract

696,269. Thermal switches. GENERAL MOTORS CORPORATION. Nov. 28, 1951 [Dec. 15, 1950], No. 27861/51. Class 38 (v) In a switch suitable for controlling split phase motors heating of a wire 50 by current passing through it allows a spring-biased lever 40 to rotate counter clockwise so that notches 56, 55 in the lever successively carry the ends of bowed springs 60, 61, formed respectively by tongues of contact springs 32, 33, past dead centre positions causing contacts 37 and 38 to snap successively upwards out of engagement with contacts 21, 22. The lever 40 may be carried by a blade spring 34 fixed in place together with the springs 32, 33 by a rivet 35, the spring 34 bearing the lever 40 downwards. The current through the wire 50 passes in parallel through the two pairs of contacts and the breaking of the one circuit at 37, 21 may reduce the current in the wire so that the contacts 38, 22 remain closed. Assuming however that both pairs of contacts are opened and that the wire 50 begins to cool. The contact 37 will first tend to close due to its tongue 60 passing through a dead-centre position but this movement is prevented by the end 66 of the spring 33 which now bears against the spring 32. Eventually both pairs of contacts snap simultaneously into the closed position. Specifications 532,576 and 591,634 are referred to.