Ground Loops Established by Capacitive Coupling
In our definition of the ground loop we said that a ground loop is created whenever a electrical path, consisting of ground wires (or shields) of a system and the d plane, exist in 16,5(a) we indicated that such a path can consist of an ohmic conducting path and the ground plan However, owing to capacitive coupling. a closed electrical path can also exist even if there is no apparently complete conducting path (i.e., even though the measurement system is ohmically connected to ground only at a single point). For example, let us examine an amplifier, as shown in Pig, 16.7 with an input signal ground connected to earth ground at point 1 and a shield surrounding the amplifier that is not connected to earth ground. Note that there is still a complete current path (loop) from the ground lead within amplifier 1 to a second ground point, 4 through the mutual capacitances connecting the ground lead and shield (C12) and the shield and the ground plane (C23) us a ground loop rough path D 3 d does indeed exist. If an ac potential difference exist between the ground points D and G a current will flow in this ground loop.