GB1493403A - Thermal protector - Google Patents

Abstract

1493403 Thermal switches TEXAS INSTRUMENTS Inc 10 Dec 1974 [14 Dec 1973] 53321/74 Heading H1N A thermal protector comprises an outer U- shaped bimetallic strip 3 with the layer 5 of lower coefficient of thermal expansion being on the inside and having one end fixed to an electrical terminal 10, and an inner U-shaped bimetallic strip 13 with the layer 15 of higher coefficient of expansion being on the inside and having one end 19 secured to an electrical terminal 10 and a free end extending outwardly beyond, and electrically insulated from, a free end 11 of the outer strip 3 and mounting an electrical contact 29 which is co-operable with an electrical contact 25 secured to another terminal 27, the arrangement being such that when the current between the terminals 10, 27 via the inner strip 13 exceeds a predetermined level the contacts 25, 29 will first be separated by the outer strip 3 and then further separated by the subsequent cooling of the inner strip 13. One end of each strip 3, 13 is spot welded at 35 to a housing 10 constituting one of the terminals, the other of which is formed by a cover 27 electrically insulated from the housing 10 and mounting the contact 25. A layer 23 of insulation is provided between the strips 3, 13 except at their fixed ends. The temperature at which the contacts 25, 29 open can be varied by deforming a stepped portion 45 of the housing 10 so as to move the strips 3, 13. The contacts 25, 29 may be formed of wire (Fig. 5, not shown). In another embodiment, the terminals are formed by pins (53, 54) (Fig. 6, not shown) extending into a glass housing (55, 60).