Abstract: A protective device includes a heating element and a low-melting metal element on a substrate, the low-melting metal element being fused by the heat generated by the heating element, and in this device the heating element and the low-melting metal element are stacked so as not to allow an insulating layer to intervene therebetween, and as a result the protective device is miniaturized and the operating time reduced without lowering the rated current.

Abstract: A protective element contains a heat-generating member and a low melting metal member on a substrate. The low melting metal member is caused to blow out by the heat generated by the heat-generating member. The number of locations on the low melting metal member which are able to blow out is larger than the number of locations which are supposed to blow out so that the protective element is endowed with a “fail-safe” function.

Abstract: To obtain a protective device that can prevent overvoltage and at the same time has an excellent safety and also to make chip type protective devices smaller in size, this invention provides a protective device comprising a substrate, a heating element provided on the substrate, an insulating layer that covers the surface of the heating element, and a low-melting metal piece provided on the insulating layer. Particularly preferably the substrate and the heating element are each formed of an inorganic material. This protective device may be used in combination with a voltage detecting means making use of a zener diode, in such a way that the heating element of the protective device is electrically excited to generate heat when the voltage detecting means detects a voltage exceeding the rated voltage, whereby an overvoltage protector can be set up.