GB760970A - Snap action electric switches - Google Patents

Abstract

760,970. Thermal switches. MIDLAND ELECTRIC MANUFACTURING CO., Ltd. Feb. 24, 1955 [Feb. 26, 1954], No. 5691/54. Class 38(5) A thermal snap action switch which is adapted so that the contacts may be reset automatically or manually includes a manually operated bar 25 which may move downwards in a recess 24 and which has two positions of rest, one at the top as shown in Fig. 1 and one midway down. A bimetallic strip 21 heated by an element 19 carries an operating piece 22. A toggle mechanism comprises an actuating member 11, a contact carrying member 10 (both pivoted on the member 8), and an overcentre spring 16. When the piece 22 moves to the left the member 11 turns anticlockwise and causes the member 10 to snap over to the right moving through the member 11, thereby opening the contacts. The member 11 returns to its original position under the action of spring 15 as the bimetal cools, but with the bar in its top position (as shown), the dead-centre line is not reached and the contacts remain set open. Movement of the bar downwards causes its sloping face to engage the projection 18 whereupon the member 10 snaps, back and closes the contacts. If however the bar 25 is initially set in its mid position, when the switch opens the projection 18 engages the bar and prevents the member 10 moving quite so far to the right, whereup as the bimetal cools and the member 11 returns to its original position the dead centre line is reached and the member 10 snaps back to close the contacts automatically. The contacts may also be opened by hand when the switch is closed by moving the bar. right down so that it engages the projection 17 on the member 11; the contacts closing again immediately on release. Figs. 4, 5 and 6 (not shown), show a plurality of similar switches in a bank, and also describe means for setting the bar 25 in its two positions.