Classification and analysis of different types of coupling
Electromagnetic compatibility - Transmission modes

Common-impedance (or common-element or galvanic) coupling occurs when the electrical currents of two separate systems follow the same path, whose impedance cannot be neglected. Figure 5, which shows two circuits sharing the same portion of ground conductor, illustrates such coupling. Through the impedance of this common conductor, the return current of one circuit causes a variation in the reference potential of the other; this voltage variation may appear in full in the expression of the output signal v _s, or it may result in the appearance of a common-mode signal.