What is a Dielectric?

A dielectric is a form of insulation between two conductors that allows polarization of charges, also known as electrostatic attraction and repulsion.

In coaxial cables, the dielectric is located between the center conductor and the outer conductor. For twisted-pair cables, it is the insulation between the conductors as well as any air or other insulating medium that surrounds the conductors.

Here are some of the terms used when discussing dielectrics:

• Dielectric Breakdown— This is when the dielectric is altered and becomes conductive. It usually happens when high voltage is applied and insulation fails.
• Dielectric Constant— This term refers to the property which determines a dielectric material’s ability to store electrostatic energy when a certain voltage is applied. The dielectric constant is also called relative permittivity.
• Dielectric Strength— This is the amount of voltage that the insulation can handle before degrading. This is a good quality because it reflects the durability of the dielectric.
• Dielectric Loss— This is the power loss caused by friction in the dielectric. The friction is created by molecules moving in an alternating electric field. Power loss is generally an undesirable property.
• Dielectric Absorption— This term refers to the build-up of electric charges when the dielectric comes in contact with an electric field. Because good dielectrics resist the flow of electrons, this is a troublesome property.

Insulation and Dielectrics

Although the terms dielectric and insulation can be used interchangeably, insulation typically describes a material with low conductivity. Dielectric, however, specifically refers to insulating material with high polarization tendencies. Dielectric properties can be an important element to consider when choosing a cable. The characteristics discussed in these definitions can either make or break the success of an application. Make sure to take them into account when choosing the appropriate cable for your specific project needs.

Want to learn more about cable components? Watch the first video in our “Cable Basics 101” series, or visit our cable engineering resources to read articles about different cable components.