INSULATION

Insulating materials are used in electric devices to keep current from flowing where it is not desired. They are simply materials with a sufficiently high resistance or sufficiently low conductance, also known as dielectric materials. Typically, plastics or ceramics are used.

When an insulator is functional, its resistance is infinite or the conductance will be zero so that current will not flows through it. If the voltage difference between two sides of the insulator becomes too large, its insulating properties may break down due to microscopic changes in the material, where it actually becomes conducting. Generally, the thicker the insulator, the higher the voltage difference it can sustain. However, temperature is important ie, plastic wire insulation may melt if the wire becomes too hot. The insulators often seen on high-voltage equipment consist of strings of ceramic bells, holding the energized wires away from other components . The shape of these bells serves to inhibit the formation of arcs along their surface. The number of bells is roughly proportional to the voltage level, though it also depends on climate.