Contact Resistance measured in milli-ohms, is the electrical resistance of a reed contact in closed state, as measured terminal to terminal, at their associated terminals. This is usually measured with a coil at 25% overdrive. Four-terminal Sensing and shielded cables should be used for accurate contact resistance measurements.
The term contact resistance refers to the contribution to the total resistance of a system which can be attributed to the contacting interfaces of electrical leads and connections as opposed to the intrinsic resistance, which is an inherent property, independent of the measurement method. This effect is often described by the term Electrical Contact Resistant or ECR. The idea of potential drop on the injection electrode was introduced by William Shockley to explain the difference between the experimental results and the model of gradual channel approximation. In addition to the term ECR, "Interface resistance", "transitional resistance", or just simply "correction term" are also used. The term "parasitic resistance" has been used as a more general term, where it is usually still assumed that the contact resistance has a major contribution.