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• Mains emissions: equivalent circuit

The basic equivalent circuit for conducted emissions testing on the mains port is shown here.

The mains connection is represented by the AMN/LISN giving a defined RF impedance between live and earth, and between neutral and earth.

The EUT contains both differential and common mode sources, generalised here as appearing in one case between live and neutral, and in the other case between both live and neutral with respect to earth.

The connection to the mains is made via a length of cable which should also be included in the model for best accuracy, but is not included in this discussion. If the apparatus is Safety Class II there is no earth wire, but common mode signals can still return via the stray capacitance to the ground plane.