symmetrical voltage

Definition:

In two-wire circuits (e.g., single-phase power supplies), the symmetrical voltage is the RFI voltage that appears between the two wires. It is sometimes referred to as differential mode voltageThe

If Va is used to denote the voltage vector between one of the power terminals and ground, Vb denotes the voltage vector between the other power terminal and ground.

Then the symmetrical voltage i.e. differential mode voltage can be expressed as the difference between Va and Vb vectors, i.e.:Va-Vb.