Insulation

Insulation. In electricity it is usual to classify substances according to their ability to conduct electricity, or, in other words, - according to their power to resist the stress caused by the separation of opposite electrifications. There is no line of separation between conductors and insulators, but if good insulation is demanded substances such as air, glass, paraffin, ebonite, shellac, or porcelain are selected. Thus the insulation material for an ordinary Leyden jar is glass; to prevent leakage from a telegraph-wire to the ground through the telegraph-posts, insulators of porcelain are used. The covering of submarine cables is of gutta-percha or some such compound, strengthened by an outer casing of wire rope. The insulation for ordinary alternating currents is generally of the above nature also; but for high potential and high frequency alternations it seems that ordinary insulators are liable to break down, small flaws rapidly increasing in size, even though at first they may not be detected. To avoid this, oil insulation has. been proposed; being fluid, its tendency is to correct any flaws that may momentarily appear.