GB1415179A - Electric switches - Google Patents

Abstract

1415179 Thermal switches GENERAL ELECTRIC CO 19 Dec 1972 [27 Dec 1971] 58542/72 Heading H1N The free end of cantilever mounted thermally responsive element 24, 26, moves upwards on heating so that double ended contact 28 on the free end of element 24, 26 breaks contact with fixed contact 34 and on further heating forces contact 48 on arm 44 attached to leaf spring 42 upwards to snap over toggle spring 50 to separate contact 48 from contact 28. On cooling, element 24, 26 moves down to re-engage contact 34, a yoke 53 on element 24, 26 pulling arm 44 down till spring 50 snaps back to re-engage contact 48 with contact 28. Element 24, 26 is of metal and has two outer limbs 24 and a centre limb 26, all joined at the free end, and at the fixed end centre limb 26 is lower than the outer limbs 24. Contact 34 is connected to terminal 30, contact 48 to terminal 38 and contact 28 to terminal 12 so that current flows through centre limb 26 heating the centre limb 26 more than the outer limbs 24 the fixed ends of which are not electrically connected to the centre limb 26 and this together with the fixed end of centre limb 26 being lower than the fixed ends of the outer limbs 24 causes the element to pivot. The device is intended to start and protect a motor M, Fig. 11. Terminal 12 is connected through an on/off switch to line L 1 , terminal 30 to the start winding and terminal 38 to the run winding. Initially all contacts are closed as shown in Fig. 2. If the on/off switch is closed, current flows through both windings until element 24, 26 pivots, breaking contact between contacts 28, 34, leaving the run winding still connected to L 1 through contacts 28, 48. If an overload occurs, element 24, 26 heats up more and pivots more to snap contact 48 upwards cutting out the run winding until element 24, 26 cools down, reclosing contacts 34, 28 and 48. Contact 34 is adjustable. Toggle spring 50 is mounted on arm 52, which may be of bimetal for ambient temperature compensation. In a second embodiment, Fig. 6, the thermal element is heated by a ribbon 64, start contact 84 is on a flexible arm adjustable by screw 107, arm 90 on which toggle spring 95 is mounted is adjustable by screw 105 and an adjusting screw 110 is in the end of yoke 108 to provide an adjustable stop for contact 88, also the circuit connections to the motor are different, L 1 being connected to contact 88, the start winding to contact 84 and the run to contact 86, although the principle of operation is the same.