A substance that will not conduct direct-current electricity: an insulator.

When cathodic protection systems are designed, it often becomes important to electrically isolate structures from each other. If sacrificial anodes are being used to protect a steel tank, for example, it is usually desirable that electric current not flow from the tank to steel pipe connected to the tank.

Isolation of these two structures is accomplished through use of a dielectric bushing, a fitting made of a substance such as nylon that does not conduct electricity.