A conventional switch device, especially from those switches using bimetallic plate to prevent from being burn when an overload is happened, generally includes a bi-metallic plate which is deformed when overloaded so as to separate the two contact points respectively located on the bimetallic plate and one of the two terminals. U.S. Pat. Nos. 5,262,748; 4,167,720; 4,937,548; 5,223,813; 5,451,729; and 5,558,211 respectively disclose safety switches. Some inherent shortcomings for these conventional safety switch devices are found. There are too many parts involved in the safety switch device and a longer period of time is required when assembling the switch device, this increases the cost of the products. The parts might be arranged inaccurately and would affect the deformation of the bi-metallic plate. Once the bi-metallic plate is deformed to cut off the circuit, because of the improper arrangement of the parts as mentioned above, the bi-metallic plate could deform to re-connect the two contact points to connect the circuit again. Because the inaccuracy of the deformation of the bi-metallic plate, the switch member does not set in the “OFF” position after the bi-metallic plate is deformed to cut off the circuit.
Therefore, it is desired to have a protection device that guides the bi-metallic plate to deform toward a desired direction and there is enough space to allow the bi-metallic plate to deform completely.