What are the components of conducted EMI?

Differential mode component Differential mode EMI appears as a voltage between the supply lines of the equipment. The resulting current circulated through the supply lines and the source. None flows through the earth conductor.

Fig.B Differential mode EMI current flow.

Common mode component Common mode EMI appears as a voltage on both lines with respect to earth. Common mode current flows through both supply lines to earth (see FigC). If the system has no protective earth connection, common mode current will flow through the capacitance between the case of the system and earth.

Fig.C Common mode EMI current flow.