GB808962A - Ambient temperature compensated electrical switch - Google Patents

Abstract

808,962. Thermal switches; snap-action switches. SQUARE D CO. Dec. 13, 1956 [Jan. 9,1956], No. 38079/56. Class 38 (5). In an overload-protection switch, a U-shaped bi-metal heated by passage of the load current, a U-shaped ambient-temperature-compensating bi-metal and a pair of longitudinally extending connecting rods are arranged in a substantially longitudinally extending manner between an abutment and an operating arm for the switch contacts. Fig. 3 shows an overload relay which opens contacts 19, 21 connected to terminals 15, 16 when an overload current passes through a heater 49 via main terminals 47, 48. Passage of the load current through the heater 49 causes one arm 35 of a floatingly mounted U-shaped bimetal to move a slidable rod 29, the other arm 37 of the bi-metal resting against an adjustable abutment 38. A shoulder on the rod 29 moves one arm 28 of a floatingly mounted, ambienttemperature-compensating bi-metal 27 and the other arm 26 of the bi-metal presses an operating rod 23 against a switching arm 17 carrying the contact 19. Overload current through the heater causes the rod 23 to press hard enough to actuate an over-centre acting resilient link 18 which opens the contacts 19, 21. The contacts 19, 21 are reset by downward movement of a plate 7 which rotates a shaft 53 through 90 degrees. This causes a part 57 of the shaft to press against the switching arm 17 and close the contacts. The plate 7 may be pinned down and the shaft 53 therefore permanently turned through 90 degrees to provide automatic resetting. In another form, Fig. 8 (not shown), the relative position of the bi-metals is reversed, i.e. the ambient-temperature-compensating bimetal is nearer the abutment 38.