Arcs in Low-Voltage A-C. Networks

The extinction of a-c. arcs at current zero is reviewed, and arc reignition characteristic and circuit reignition characteristic are defined. From a study of arc reignition characteristics of short arcs remote from insulation it is concluded that such arcs are incapable of interrupting practical low-voltage a-c. network circuits. The extinction of arcs in practical network cables is then ascribed to the deionizing action of gas blasts coming from decomposing adjacent insulation. Experiments with arcs in cables, and arcs between parallel plates remote from insulation, and closely bounded by insulation, confirm this view. Inorganic insulating materials may also assist in arc extinction by generating gas blasts by their decomposition. Of the various inorganic materials tried, boric acid was the most effective. Charring of organic insulation may be expected to cause it to lose its arc extinction aiding characteristic.