THERMAL PROTECTIVE DEVICE HAVING RAPID RESPONSE TO SUDDEN HIGH OVERLOADS AND DELAYED RESPONSE TO MODERATE OVERLOADS

摘要

1,083,650. Thermal switches. CANADIAN GENERAL ELECTRIC CO. Feb. 15, 1966 [May 15, 1965], No. 6505/66. Heading H2B. In a switch for protecting a motor against overload, a bimetal strip 22 is loosely mounted on a further bimetal strip 27 secured to the wall 18 of a housing 1. The high expansion sides of the two strips is to the left, and strip 22 is loosely connected to a support 28 slidable in the housing to actuate a snap-action switch. Under severe overload, the strip 22 is heated by a heater 12 and its lower end bends to the right to open contacts 72, 74 and close contacts 73, 75. If a plunger 6 is in the position shown, the contacts have to be reset by depression of the plunger, but if the plunger is held depressed by a spring (7), (Fig. 1, not shown), the contacts are automatically reset on cooling of strip 22. In the event of a lesser, prolonged overload, the upper end of strip 27 bends to the right, and strip 22 pivots clockwise about an adjustable stop 45 to move its lower end to the left, thereby effectively delaying actuation of the switch. Ambient temperature compensation may be provided by making switch part 46 of bimetal. The inner walls of compartment 13 may be lined with a heat-reflecting layer.