Patent GB-476276-A (GB)
Title: Improvements in or relating to thermally-controlled electric circuit-breakers
IPC: A63B53/02
Filed: 1937-01-12
Abstract: 476,276. Thermal switches; automatic circuit breakers ; protective cut - out systems. LELAND ELECTRIC CO. Jan. 12, 1937, No. 941. Convention date, Feb. 13, 1936. [Class 38 (v)] An automatic circuit-breaker for protecting a motor or similar device from injury by excessive heat comprises a contactor 17 biassed to circuit-opening position, a controlling member 22 adapted to move the contactor to circuit-closing position and to be moved in the other direction by the contactor when the circuit opens, a support 20 for the member 22, means such as a one-way clutch interposed between the member and the support to permit movement of the member in the circuitclosing direction and normally prevent the movement of the member in the other direction and a thermal element adapted to release the controlling member for movement in the circuit-opening direction when subjected to abnormal temperature. In the arrangement shown, the circuit-breaker is mounted on an insulating base 15 inside the casing 10 of a motor to be protected, and comprises a pair of movable contactors 17, 17a co-operating with normally stationary but yieldable contacts 16, 16a, both movable contactors being under the control of the controlling member 22. The support 20 is mounted on a stud 18 which forms one end of a heat conducting rod 19, and is normally secured to the stud by a fusible binder 21 of solder of low melting point. The one-way clutch between the member 22 and its support 20 comprises a spring 24 coiled about and attached to a reduced portion 23 of the support 20, the spring being in frictional engagement with the inner surface of the member 22, so that the tendency of the member to rotate in the circuit-opening direction will expand the spring and cause it to act as a clutch. The contactors 17, 17a are in the form of curved springs secured at one end to studs 25, 27, while the other ends of the springs engage lugs 28 on the controlling member 22, as shown in Fig. 5, and tend to rotate the member to the circuit-opening position. If the temperature rises to a point sufficient to meet the binder 21, the support 20 is released and the contactors together with the controlling member rotate to the open position. When the temperature falls, the binder resets, and the controlling member can be rotated in the opposite direction to reclose the circuit. For this purpose a resetting member 29 is rotatably mounted on the outer end of the controlling member 22, and is provided with radial lugs 30 adapted to engage lugs 31 on the controlling member, which extend outwardly beyond the lugs 28. The resetting member also carries curved insulating flanges 32 which are moved between the stationary and movable contacts when the resetting member is rotated in the closing direction, so that the circuit does not close until the resetting member has been retracted into its inoperative position and it is impossible to hold the circuit closed by hand. The resetting member may be used to open the circuit at any time by rotating it to its operative position, in which it is held by the friction between the flanges and the stationary contacts until it is positively withdrawn. The resetting member may be arranged to project through the casing of the motor so as to be directly operable by hand, but in the construction shown, a separate actuating member 33 is provided, having a knob 35 outside the casing and a tongue and groove connection with the resetting member. In a modification, Fig. 10 (not shown), the stationary and movable contacts of each pair are formed in one piece and supported by a single terminal stud. The application of the circuit-breaker to a motor having a main winding 48 and an auxiliary starting winding 54 is shown in Fig. 11. In this application, the contacts 16, 17 are connected in the starting circuit, which circuit also includes a heating coil 36 mounted on the rod 19. The contacts 16a, 17a are in the circuit of the main winding 48. When the motor has run up to speed, a centrifugal switch 37 automatically interrupts the starting circuit.