Patent GB-484800-A (GB)
Title: Improvements in or relating to electric overload released switches
IPC: H01H73/56
Filed: 1936-11-10
Abstract: 484,800. Electrically released switches. TAYLOR, S. Nov. 10, 1936, No. 30623. [Class 38 (v)] An overload-released switch of the kind wherein is provided a thermo-magnetic element comprising a coiled bimetal-strip conductor anchored at one end, the other and movable end being associated with release mechanism so as to be actuated by the heating and/or magnetic effect of the strip-current, has means whereby the movable end of the strip is subjected to a magnetic force axial of the coil and generated by the coil-current, and further means whereby axial movement of the movable end of the strip operates release mechanism. As applied to a screw-plug circuit-breaker, the insulating body 1 is preferably of mouldable material as glass, vulcanite, or synthetic resin, and is provided with a brass or other metal threaded part 2 which retains an insulating disc 4 carrying metal brackets 5, 6 on its opposite sides. A central terminal screw 8 secures a cup-like steel or other magnetic piece 7 with a conical central boss, with which co-operates an iron plunger 15 secured to the upper coil of a currentcarrying bimetal-strip 14 of conical-helix form which is secured to the piece 7 by its lower coil. An extension 15a on the plunger 15 is guided in an arm 6a on the bracket 6, and serves as a retaining part for the arm 17b of a lever 17, which is pivoted at 18 on lugs 6b on bracket 6, is controlled by a return-spring 19, and divided to form a pair of contacts 17a. The co-operating contact 13 is pivoted at 12 to lugs on bracket 5 and urged to the position shown by a spring 13a, the bracket 5 being connected at 11 to the thread 2. Springs 13a, 19 are preferably of brass or bronze. On overload, the coil-strip 14 winds into a tighter coil, so rotating and pulling down the plunger 15, whereas on short-circuit, the coil flux causes the plunger to be attracted to the boss of piece 7. In the former case the release is delayed and may be substantially independent of magnetic attraction, whereas in the latter case, the release is instantaneous and may be substantially independent of thermal action. In the released position, contacts 17a engage under the button 3 which, to reset, is depressed and released. The former action causes the arm 17b to re-engage behind extension 15a and, by engaging an arm 13b integral with arm 13, causes the latter to move downwards away from contacts 17a. On release of the button spring 13a returns 13 to the position in which it engages contacts 17a. The arrangement provides a free release the nature of which can be ascertained, since reclosure on overload would be prevented by the failure of 17b to reengage 15a, whereas a short-circuit would be detected by the immediate tripping occurring when 13 re-engaged 17a. Figures of performance and rating are given in the Specification, which refers also to adjustment of the delay-action, and to tripping by extraneous heat such as that due to a fire. The conical may be replaced by a flat coil adapted to rotate a plunger having either a bevelled releasing-end or a cross-pin working on a cam on the lower side of the guide hole so as to be moved axially by the thermal rotation while being free to move axially under electromagnetic force. The invention is also adaptable to cartridge-type holders. Contacts.-Arm 13 may be of copper-beryllium alloy. Indicators.-Button 3 is transparent so that the switch-condition may be observed.