Overcurrent and short circuit protection device

Claim 1

Improved apparatus for electrical overcurrent and short circuit protection of the type in which a fusible wire is arranged in an arc-quenching chamber between first and second electrodes which, after the fusible wire is melted through, forms with the arc a current loop generating magnetic forces which act to elongate the arc, comprising: a. a pair of horn electrodes coupled to the first and second electrodes; b. an inner arc chamber comprising: 1. first and second sidewalls comprising extensions of said pair of horn electrodes; 2. an end wall abutting said first and second sidewall; 3. a bottom wall covering one side of said horn electrodes and said side walls and endwalls; 4. a top wall covering the other side of said horn electrodes, side walls and end wall; 5. said top and bottom walls being disposed parallel to each other and forming a gap which is of a sufficiently small thickness such that the voltage current characteristic of the arc has a descending portion to a minimum value with increasing current, after which it then rises for large currents and, wherein, 6. said top, bottom side walls and end walls each contain a plurality of mutually parallel holes having a diameter in the range of 0.8 to 2.5 mm and having a total cross section which is 30 to 50% of the inside area of said arc-quenching chamber; and c. an outer arc-quenching chamber surrounding said inner arc-quenching chamber, said outer arc-quenching chamber having at least one wall provided with mutually parallel holes.