Patent GB-438617-A (GB)
Title: Improvements in or relating to thermostatically-controlled electromagnetic switch-operating devices
IPC: H01H35/24
Filed: 1934-06-20
Abstract: 438,617. Antomatic circuit-breakers. WALKER, C. BELL-, 38, South Bar, Banbury, Oxfordshire, and SMITH & SONS, (MOTOR ACCESSORIES), Ltd., S., Cricklewood Works, Cricklewood, London. June 20, 1934, No. 18268. [Class 38 (v)] In a thermostatically - controlled circuitbreaker of the type in which a switch arm is moved automatically by electromagnetic means into one of two alternative positions under the control of a thermostatic device and is retained in position by means of a latch which is also controlled automatically by the thermostatic device, the electromagnetic device is brought into operation by a control element of the thermostatic device moving in one direction to move the switch arm into the position in which it is held by the latch and the control element of the thermostatic device is mechanically coupled with the latch for releasing the latter by movement of the control element in the opposite direction. At least a part of the thermostatic device may comprise an expansion element remote from the switch and additional thermostatic means may be provided adjacent to the switch to compensate for local temperature variations. As shown, the switch arm 12 in the closed position is held by a self-acting latch 17, the operating electromagnet 11 having a circuit maintained at contacts 29, 30, the former of which is carried by a contact lever pivoted to the latch 17 at 28. Springs 33, 36 for the contact lever and latch are both attached to a stirrup 35 bearing on an axially movable rod 21 attached to the thermostatic control member which consists of a bellows 43 in a chamber 45 connected by a capillary tube 46 to the main expansion chamber 47. On the contraction of a liquid, such as toluene, in this chamber, the rod 21 is raised, a collar 22 on which separates contacts 29, 30 in the electromagnet circuit and subsequently raises the latch 17 to release the switch arm, which then opens by gravity. On the return movement of the rod 21 due to increased temperature of the chamber 47, the contacts 29, 30 are permitted to reclose, so energizing the electromagnet and attracting the switch arm, which is then automatically latched by the member 17 in the closed position. This latching operation is assisted by a blade spring 19 carried by the switch arm. To vary the temperature setting, a collar 51, in an axial slot of which a projecting key attached to the lower end of the rod 21 slides axially, is rotated by a knob 54, its adjusted position being indicated by a graduated scale. This rotation moves the threaded upper end of the rod 21 upwardly or downwardly within the internally-threaded sleeve 41 attached to the movable end of the bellows 43 so as to vary the distance the rod travels before the collar 22 causes operation of the contact arm and latch. The relatively fixed contact 30 is made adjustable relatively to its co-operating contact 29 by being formed as an eccentric. A bimetallic strip 24 attached to the latch 17 bears on the collar 22 of the rod 21 to couple it to the latch in a manner which compensates for ambient temperature variations. If the circuit-breaker is to be arranged for release with increasing and not decreasing temperature, the rod 21 with its upper and lower attachments is reversed in relation to the casing 10, a second collar 23 then producing the control operations.