GB703308A - Improved temperature responsive electric switch - Google Patents

Abstract

703,308. Protective cut-out arrangements; thermal switches. GENERAL MOTORS CORPORATION. July 1, 1952 [July 13, 1951], No. 16498/52. Addition to 591,634. Class 38(5) In a modification of the motor control device according to the parent Specification the thermoresponsive device which shunts part of the current to the control device during normal running of the motor is inoperative during starting and is rendered operative by the opening of the starting winding circuit. A rigid frame 20 carries leaf springs 22, 23, the former carrying opposed contacts 25, 26, cooperating with fixed contacts 27, 28 and the latter a contact 39 co-operating with a fixed contact 40. An actuator 35 biased counter-clockwise by a leaf spring 21 is also carried by the frame 20 and forms an abutment for dead-centre springs 47, 36 on the leaf springs 22, 23. A thermal expansion element 50 in the form of a wire is connected between actuator 35 and a terminal 51 on the frame and is so tensioned that when no current is flowing it retains actuator 35 against spring 21 in such a position that contacts 25, 27 and 39, 40 are closed, as shown. Contacts 26, 28 in circuit with a flexible, bimetallic plate 60 forming the shunting device, are open. When the motor is started, the heavy current flowing through the starting and running windings 30, 45, blades 22, 23, and element 50 causes the latter to expand and allow the actuator 35 to swing sufficiently to actuate blade 22 and open the starting winding, by which time the motor will have attained its normal operating speed. At the same time contacts 26, 28 are closed, shunting part of the current through plate 60. If an overload occurs, element 50 expands further and actuates blade 23 to open contacts 39, 40 and stop the motor. This further expansion of element 50 alternatively may be brought about or accelerated by flexing of plate 60 due to abnormal rise in the temperature of the motor, causing contacts 62, 63 to open and the whole of the current to flow through element 50.