Improvements in and relating to electrically heated thermal control elements, specially applicable to expansion type thermal elements forming overload and/or no-volt devices for electric circuit-breakers, contactors and the like

摘要

446,672. Thermal switches ; automatic circuit-breakers. COX, F. B., 65, Fleet Street, Liverpool. Oct. 31, 1934, No. 31171. [Class 38 (v)] A thermal switch for controlling an automatic circuit-breaker comprises a bimetallic strip S, Fig. 1, fixed at one end to a terminal T1 and at the other end to a heating strip H also connected to terminal T1. The free ends of strips S, H are connected by a lead F to a terminal T2. When an excess current passes through the strips S and H they bend to the right and tilt a bell-crank lever D to separate contacts 4, 5 in the hold-on circuit of a circuitbreaker. The heating element H may be wound on a tube surrounding the strip S. In the arrangement shown in Fig. 2, on failure of voltage across the terminals T1, T2, strip S bends to the left and rotates lever E to lift a detent 11 and release a circuit-breaker 12. The point 1 passes the end 7 of lever E, and the circuit-breaker may be reset before strip S is heated, as the return movement thereby causes an idle movement of lever E. In another arrangement the point 1 is arranged between two levers E which are operated respectively due to overload and no-volt conditions, to open the circuit of a hold-on coil.