GB202321A - Improvements in and relating to thermally controlled electric switches - Google Patents

Abstract

202,321. British Thomson - Houston Co., Ltd., (Assignees of Brobst, J. E.). Aug. 11, 1922, [Convention date]. Automatic circuit - breakers; protective arrangements. - In a thermally - operated overload circuit-breaker comprising a m a i n switch maintained closed electromagnetically and a thermally released circuit-breaker, which, on overload, breaks the maintaining-circuit and allows the main switch to fall to the off position, the off movement serves to restore the thermal relay to the closed position and to reset it under the control of the thermal means. In the arrangement shown, for protecting the motor 12, the main switch 11 is brought into the closed position by distant push-button control, and is maintained by alternative connection through the back contacts 18. When the thermal strip 17 bends under the heating action of the coil surrounding it, the contact-arm 13 escapes, and the maintaining circuit of the main switch is broken at the contacts 14, 15. In consequence, the main switch assumes the off position, and in doing so presses a plunger 19 which rotates the arm 13 into the closed and reset position shown. The main switch may be reclosed by momentarily closing the starting push-button. Alternatively, the main switch, located within a casing may be operated by an external handle and maintained electromagnetically, the return movement of the handle acting through a pin and lever to depress the plunger 19 for resetting.