A voltage of any amplitude or frequency that is measured between the phase conductor and the ground conductor or the neutral conductor and the ground conductor. Neutral to ground voltage is a common mode component that frequently causes computer system malfunction. Neutral to ground voltages should always be limited to .5 volts (one half of one volt) or less.
The voltage common to both sides of a differential circuit pair. The differential voltage across the circuit pair is the desired signal, whereas the common voltage signal is the unwanted signal which may have been coupled into the transmission pair.