Protector for electric circuits

A current-limiting electric fuse that comprises a housing which has an elongated passage therein, terminals which are located at the ends of said passage, a fusible element which is disposed within said passage and which is electrically connected to said terminals, said fusible element being essentially composed of copper or silver and having at least one weak spot therein, said fusible element responding to a prolonged low but potentially-harmful overload or to a short circuit or heavy overload to open, and arc-extinguishing material which directly contacts said weak spot and the inner surface of said passage and which substantially fills said passage, said weak spot having at least one portion thereof which hs displaced from said inner surface of said passage but said one portion being displaced from said inner surface by a distance less than 64 millimeters, said weak spot having said one portion thereof displaced from each of said terminals a distance greater than eighty millimeters, said housing being made from an inorganic ceramic material which has a thermal conductivity greater than thirty thousandths of a calorie per square centimeter of cross section per centimeter of length per second of time per degree centigrade, said housing having the major portion of the outer surface thereof exposed to a cooling medium to enable said major portion of said outer surface to radiate heat to said cooling medium, said weak spot generating heat whenever current flows through said fusible element, said arc-extinguishing material absorbing appreciable amounts of heat and transferring most of said appreciable amounts of said heat to said inner surface of said passage, said housing transferring appreciable amounts of the heat which it receives from said arc-extinguishing material to said outer surface thereof to enable said outer surface to radiate heat to said cooling medium, said weak spot having a temperature in excess of 80 percent of its melting temperature whenever said electric fuse is operated at its maximum continuous current carrying capacity but said arc-extinguishing material and said housing transferring so much heat to said outer surface of said housing that the temperature of said inner surface of said passage remains below 350.degree.C., the temperature of said weak spot rising to the melting temperature of said fusible element whenever said fusible element responds to a prolonged but potentially-harmful overload to open but said arc-extinguishing material and said housing transferring so much heat to said outer surface of said housing that the temperature of said inner surface of said passage remains below 350.degree.C.

A current-limiting electric fuse that comprises a housing which has an elongated passage therein, terminals which are located at the ends of said passage, a fusible element which is disposed within said passage and which is electrically connected to said terminals, said fusible element being essentially composed of copper or silver and having at least one weak spot therein, said fusible element responding to a prolonged low but potentially-harmful overload or to a short circuit or heavy overload to open, and arc-extinguishing material which directly contacts said weak spot and the inner surface of said passage and which substantially fills said passage, said weak spot having at least one portion thereof which is displaced from said inner surface of said passage but said one portion being displaced from said inner surface by a distance less than 64 millimeters, said weak spot having said one portion thereof displaced from each of said terminals a distance greater than 80 millimeters, said housing being made from an inorganic ceramic material which has a thermal conductivity greater than thirty thousandths of a calorie per square centimeter of cross section per centimeter of length per second of time per degree centigrade, said housing having the major portion of the outer surface thereof exposed to a cooling medium to enable said major portion of said outer surface to radiate heat to said cooling medium, said weak spot generating heat whenever current flows through said fusible element, said arc-extinguishing material absorbing appreciable amounts of heat and transferring most of said appreciable amounts of said heat to said inner surface of said passage, said housing transferring appreciable amounts of the heat which it receives from said arc-extinguishing material to said outer surface thereof to enable said outer surface to radiate heat to said cooling medium, said weak spot having a temperature in excess of eighty percent of its melting temperature whenever said electric fuse is operated at its maximum continuous current carrying capacity but said arc-extinguishing material and said housing transferring so much heat to said outer surface of said housing that the temperature of said inner surface of said passage remains below 350.degree.C., the temperature of said weak spot rising to the melting temperature of said fusible element whenever said fusible element responds to a prolonged but potentially-harmful overload to open but said arc-extinguishing material and said housing transferring so much heat to said outer surface of said housing that the temperature of said inner surface of said passage remains below 350.degree.C., said fusible element being the only fusible element within said passage, and the width of said fusible element being greater than seventy-five percent of the diameter of said passage.

A current-limiting electric fuse that comprises a housing which has an elongated passage therein, terminals which are located at the ends of said passage, a fusible element which is disposed within said passage and which is electrically connected to said terminals, said fusible element being essentially composed of copper or silver and having at least onen weak spot therein, and arc-extinguishing material which directly contacts said weak spot and the inner surface of said passage and which substantially fills said passage, said housing being made from an inorganic ceramic material which has a thermal conductivity greater than thirty thousandths of a calorie per square centimeter of cross section per centimeter of length per second of time per degree centigrade, said housing having the major portion of the outer surface thereof exposed to a cooling medium to enable said major portion of said outer surface to radiate heat to said cooling medium, said weak spot generating heat whenever current flows through said fusible element, said arc-extinguishing material absorbing appreciable amounts of said heat from said weak spot and transferring most of said appreciable amounts of said heat to said inner surface of said passage, said housing transferring appreciable amounts of the heat which it receives from said arc-extinguishing material to said outer surface thereof to enable said outer surface to radiate heat to said cooling medium, said weak spot having a temperature in excess of eighty percent of its melting temperature whenever said electric fuse is operated at its maximum continuous current carrying capacity but said arc-extinguishing material and said housing transferring so much heat to said outer surface of said housing that the temperature of said inner surface of said passage remains below 350.degree.C., the temperature of said weak spot rising to the melting temperature of said fusible element whenever said fusible element responds to a low but potentially-harmful overload to open but said arc-extinguishing material and said housing transferring so much heat to said outer surface of said housing that the temperature of said inner surface of said passage remains below 350.degree.C.

A current-limiting electric fuse that comprises a housing which has an elongated passage therein, terminals which are located at the ends of said passage, a fusible element which is disposed within said passage and which is electrically connected to said terminals, said fusible element being essentially composed of copper or silver and having at least one weak spot therein, and arc-extinguishing material which directly contacts said weak spot and the inner surface of said passage and which substantially fills said passage, said weak spot having at least one portion thereof which is displaced from said inner surface of said passage but said one portion being displaced from said inner surface by a distance less than 64 millimeters, said housing being made from an inorganic ceramic material which has a thermal conductivity greater than thirty thousandths of a calorie per square centimeter of cross section per centimeter of length per second of time per degree centigrade, said housing having the major portion of the outer surface thereof exposed to a cooling medium to enable said major portion of said outer surface to radiate heat to said cooling medium, said weak spot generating heat whenever current flows through said fusible element, said arc-extinguishing material absorbing appreciable amounts of said heat from said weak spot and transferring most of said appreciable amounts of said heat to said inner surface of said passage, said housing transferring appreciable amounts of the heat which it receives from said arc-extinguishing material to said outer surface thereof to enable said outer surface to radiate heat to said cooling medium, said weak spot having a temperature in excess of 80 percent of its melting temperature whenever said electric fuse is operated at its maximum continuous current-carrying capacity but said arc-extinguishing material and said housing transferring so much heat to said outer surface of said housing that the temperature of said inner surface of said passage remains below 350.degree.C., the temperature of said weak spot rising to the melting temperature of said fusible element whenever said fusible element responds to a prolonged low but potentially-harmful overload to open but said arc-extinguishing material and said housing transferring so much heat to said outer surface of said housing that the temperature of said inner surface of said passage remains below 350.degree.C.

A current-limiting electric fuse that comprises a housing which has an elongated passage therein, terminals which are located at the ends of said passage, a fusible element which is disposed within said passage and which is electrically connected to said terminals, said fusible element being essentially composed of copper or silver and having at least one weak spot therein, and arc-extinguishing material which directly contacts said weak spot and the inner surface of said passage and which substantially fills said passage, said housing being made from an inorganic ceramic material which has a thermal conductivity greater than thirty thousandths of a calorie per square centimeter of cross section per centimeter of length per second of time per degree centigrade, said housing having the major portion of the outer surface thereof exposed to a cooling medium to enable said major portion of said outer surface to radiate heat to said cooling medium, said weak spot generating heat whenever current flows through said fusible element, said arc-extinguishing material absorbing appreciable amounts of said heat from said weak spot and transferring most of said appreciable amounts of said heat to said inner surface of said passage, said housing transferring appreciable amounts of the heat which it receives from said arc-extinguishing material to said outer surface thereof to enable said outer surface to radiate heat to said cooling medium, the temperature of said weak spot rising to the melting temperature of said fusible element whenever said fusible element responds to a prolonged low but potentially-harmful overload to open but said arc-extinguishing material and said housing transferring so much heat to said outer surface of said passage that the temperature of said inner surface of said passage remains below 350.degree.C.

A current-limiting, single-element, dual-function, electric fuse that comprises a housing which has an elongated passage therein, terminals which are located at the ends of said passage, a fusible element which is disposed within said passage and which is electrically connected to said terminals, said fusible element being essentially composed of copper or silver and having at least one weak spot therein, said fusible element responding to a prolonged low but potentially-harmful overload or to a short circuit or heavy overload to open, arc-extinguishing material within said passage, said weak spot having at least one portion thereof which is displaced from said inner surface of said passage but said one portion being displaced from said inner surface by a distance less than sixty-four millimeters, said weak spot having said one portion thereof displaced from each of said terminals a distance greater than 80 millimeters, said housing being made from an inorganic ceramic material which has a thermal conductivity greater than thirty thousandths of a calorie per square centimeter of cross section per centimeter of length per second of time per degree centigrade, and means to move a cooling medium into engagement with said outer surface of said housing to absorb heat from said outer surface, said means forcing said cooling medium to move into engagement with said outer surface of said housing to absorb heat from said outer surface throughout the time said current-limiting, single-element, dual-function, electric fuse is carrying current, said housing having the major portion of the outer surface thereof exposed to said cooling medium to enable said major portion of said outer surface to transfer heat to said cooling medium, said weak spot generating heat whenever current flows through said fusible element, said arc-extinguishing material absorbing appreciable amounts of said heat and transferring most of said appreciable amounts of said heat to said inner surface of said passage, said housing transferring appreciable amounts of the heat which it receives from said arc-extinguishing material to said outer surface thereof to enable said outer surface to transfer heat to said cooling medium, said weak spot having a temperature in excess of 80 percent of the melting temperature of said fusible element whenever said electric fuse is operated at its maximum continuous current carrying capacity.

A current-limiting single-element, dual-function, electric fuse that comprises a housing which has an elongated passage therein, terminals which are located at the ends of said passage, a fusible element which is disposed within said passage and which is electrically connected to said terminals, said fusible element being essentially composed of copper or silver and having at least one weak spot therein, said fusible element responding to a prolonged low but potentially-harmful overload or to a short circuit or heavy overload to open, arc-extinguishing material within said passage, said weak spot having at least one portion thereof which is displaced from said inner surface of said passage but said one portion being displaced from said inner surface by a distance less than 64 millimeters, said weak spot having said one portion thereof displaced from each of said terminals a distance greater than eighty millimeters, said housing being made from an inorganic ceramic material which has a thermal conductivity greater than thirty thousandths of a calorie per square centimeter of cross section per centimeter of length per second of time per degree centigrade, and means to move a cooling medium into engagement with said outer surface of said housing to absorb heat from said outer surface, said means forcing said cooling medium to move into engagement with said outer surface of said housing to absorb heat from said outer surface throughout the time said current-limiting single-element, dual-function, electric fuse is carrying current, said housing having the major portion of the outer surface thereof exposed to said cooling medium to enable said major portion of said outer surface to transfer heat to said cooling medium, said weak spot generating heat whenever current flows through said fusible element, said arc-extinguishing material absorbing appreciable amounts of said heat and transferring most of said appreciable amounts of said heat to said inner surface of said passage, said housing transferring appreciable amounts of the heat which it receives from said arc-extinguishing material to said outer surface thereof to enable said outer surface to transfer heat to said cooling medium, said weak spot having a temperature in excess of eighty percent of the melting temperature of said fusible element whenever said electric fuse is operated at its maximum continuous current carrying capacity, said thermal conductivity of said inorganic ceramic material of said housing limiting the temperature gradient between said inner and outer surfaces of said housing to less than 200.degree.C.

A current-limiting, single-element, dual-function, electric fuse that comprises a housing which has an elongated passage therein, terminals which are located at the ends of said passage, a fusible element which is disposed within said passage and which is electrically connected to said terminals, said fusible element being made from a material which has a high melting temperature, said fusible element responding to a prolonged low but potentially-harmful overload or to a short circuit or heavy overload to open, and arc-extinguishing material within said passage, said housing being made from an inorganic ceramic material which has a thermal conductivity greater than thirty thousandths of a calorie per square centimeter of cross section per centimeter of length per second of time per degree centigrade, said housing having the major portion of the outer surface thereof exposed to a cooling medium to enable said major portion of said outer surface to radiate heat to said cooling medium, said fusible element generating heat whenever current flows through said electric fuse, said arc-extinguishing material absorbing appreciable amounts of said heat and transferring most of said appreciable amounts of said heat to said inner surface of said passage, said housing transferring appreciable amounts of the heat which it receives from said arc-extinguishing material to said outer surface thereof to enable said outer surface to radiate heat to said cooling medium, at least one portion of said fusible element having a temperature in excess of eighty percent of the melting temperature of the material of said fusible element whenever said electric fuse is operating at its maximum continuous current carrying capacity.

A current-limiting, single-element, dual-function, electric fuse that comprises a housing which has an elongated passage therein, terminals which are located at the ends of said passage, a fusible element which is disposed within said passage and which is electrically connected to said terminals, said fusible element being essentially composed of copper or silver and having at least one weak spot therein, said fusible element responding to a prolonged low but potentially-harmful overload or to a short circuit or heavy overload to open, and arc-extinguishing material which directly contacts said weak spot and the inner surface of said passage and which substantially fills said passage, said weak spot being displaced from said inner surface of said passage and also being displaced from both of said terminals, said weak spot being displaced from said inner surface by a distance smaller than the distance by which said weak spot is displaced from each of said terminals, said housing being made from an inorganic ceramic material which has a thermal conductivity greater than thirty thousandths of a calorie per square centimeter of cross section per centimeter of length per second of time per degree centigrade, said housing having the major portion of the outer surface thereof exposed to a cooling medium to enable said major portion of said outer surface to radiate heat to said cooling medium, said weak spot generating heat whenever current flows through said fusible element, said arc-extinguishing material absorbing appreciable amounts of heat and transferring most of said appreciable amounts of said heat to said inner surface of said passage, said housing transferring appreciable amounts of the heat which it receives from said arc-extinguishing material to said outer surface thereof to enable said outer surface to radiate heat to said cooling medium.