GB841054A - A thermally operated electric switch - Google Patents

Abstract

841,054. Thermal switches; snap-action switches. JACKSON INDUSTRIES Ltd. (Fischer, K.). Sept. 28, 1956, No. 29723/56. Class 38 (5). A thermally-sensitive element acts on a switch lever pivoted on a rockable lever or cradle against a return-spring between the levers, the rockable cradle being normally held against a stop by a stronger restoring spring and movable to prevent excess pressure being applied to the contacts. The thermally-sensitive element consists of a tube 14 and a rod 13 which has a head 12 engaging a switch lever 11 pivoted at 10 on a cradle 5 pivoted at 4 on a fixed bracket 3. A spring 9 urges the cradle 5 against an adjustable stop screw 6 and a relatively weaker spring 15 urges the lever 11 to the position shown in Fig. 1, wherein the end 43 of the lever 11 engages a stop surface 17 on the cradle 5. The lever 11 carries an insulator 18 supporting a fixed contact 20 and a bracket 22 for the pivots 23 of a rocker 24 which coacts with a snap-action spring 27, 28 carrying a moving contact 26. When the head 12 is moved downward the lever 11 is moved against the action of the spring 15 and an adjustable screw 29 on the cradle 5 engages the rocker 24 to snap open the contacts 20, 26. The temperature setting depends upon the position of the cradle 5 and is set by the stop 6. On further downward movement of the head 12 the lever 11 engages a stop-screw 16 so that the cradle and lever move together against the action of the spring 9. During the return movement the stronger spring 9 first restores the cradle and on continued movement of the lever 11 the downward bias of spring 28 causes the contacts to snap closed. The snap-action switch may be omitted and contacts located at 17 and 43. Fig. 4 shows a cam 34 coupled to the adjustable screw 6 and acting on a contact-spring 37 to operate contacts 39, 40 connected in the second pole of the power circuit so that both poles may be disconnected on rotation of the screw 6.