GB882105A - Thermally responsive snap-acting electric switch - Google Patents

Abstract

882,105. Thermal switches. TEXAS INSTRUMENTS Inc. Dec. 6, 1957 [April 8, 1957], No. 38095/57. Class 38 (5). Contacts 36, 38 carried on terminals 40, 42 fixed in a base 12 are bridged by contacts 28, 30 on a bimetallic disc 20 which is mounted on a post 18 threadedly engaged in a bush 16 in the base 12. Heating, such as by current overload, causes disc 20 to snap upwards into the position shown in Fig. 3; normal fall of temperature is preferably insufficient to cause the disc to return and resetting is effected by a push-button 54 which depresses a resetting member 56 having two projections 58 and 60 to engage disc 20. A projection 62 on member 56 and a corresponding projection (not shown) on disc 20 engage in a groove 66 in the side wall of base 12 to prevent rotation of members 56 and 20. The flange 26, which holds disc 20 on to the post 18, acts as a stop to limit the downward motion of member 56 such that it cannot be held in engagement with disc 20 when the latter has snapped downwards (Fig. 5), and the switch is thus rendered trip-free, i.e. the contacts 36, 38 cannot be kept bridged by holding button 54 depressed when the disc 20 is above the maximum resetting temperature. The button 54 is biased downwardly by spring 86 which also serves to hold member 82 against a rubber gasket 74 and cover 72. The spring bias is such, however, that it is overcome by disc 20 when actuated (Fig. 3), and hence the position of button 54 indicates the condition of the switch, and a coloured band 88 may be provided on the button 54 to render its position more obvious. Specification 178,103 is referred to.