Electrical contact resistance is an important characteristic of the contact in certain components, such as connectors, switches, slip rings, and relays. Ordinarily, contact resistance is required to be low and stable for proper functioning of many devices or apparatus in which the component is used. It is more convenient to determine contact resistance with a probe than to incorporate the contact material into an actual component for the purpose of measurement. However, if the probe contact material is different from that employed in the component, the results obtained may not be applicable to the device.

Information on contact resistance is useful in materials development, in failure analysis studies, in the manufacturing and quality control of contact devices, and in research.

Contact resistance is not a unique single-valued property of a material. It is affected by the mechanical conditions of the contact, the geometry and roughness of contacting surfaces, surface cleanliness, and contact history, as well as by the material properties of hardness and conductivity of both contacting members. An objective of this practice is to define and control many of the known variables in such a way that valid comparisons of the contact properties of materials can be made.

In some techniques for measuring contact resistance it is not possible to eliminate bulk resistance, that is, the resistance of the metal pieces comprising the contact and the resistance of the wires and connections used to introduce the test current into the samples. In these cases, the measurement is actually of an overall resistance, which is often confused with contact resistance.