| impedance at a given frequency between a specified point in a system or in an installation or in equipment and reference earth
NOTE 1 – Reference earth is defined in IEC 60050-195. In practice, a reference point can be substituted to earth, for example the chassis.
NOTE 2 – The common mode rejection ratio of an instrument is dependent on the impedances between the input terminals and earth. Each of these impedances is called a common mode impedance.