Equipment reliability might be significantly improved through the effective prediction of equipment degradation. To evaluate the degree to which an electrical machine has degraded, it is necessary that one is able to measure the values of the most important physical parameters characterizing a specific condition. This chapter focuses on the physical conditions of the materials that the components of electrical equipment are made of. The electrical equipment include HV and MV electrical equipment, such as GIS, HV circuit breakers (CBs), power transformers, and MV switchgear and CBs. The chapter discusses which physical conditions of the materials are most definitive in providing proper working conditions for different electrical machines and their important parts, and therefore are very important to evaluate. Multiple techniques are developed to measure various physical parameters off-line, online, and remotely. Since some physical conditions may be determined only by off-line testing, the chapter also discusses a number of testing techniques.