A ground loop can be the result of two devices being connected that are both to be at the same potential, often ground. These usually become noticeable in the form of more or less strong low-frequency interference of the actual signal.
The reason for this is that a closed loop (ground loop) is created where a current IMis induced by alternating magnetic fields (transformer principle). This in turn causes a voltage in the total resistance R of the ground conductor that interferes with the actual Us signal.
For more detailled information please refer to: http://en.wikipedia.org/wiki/Ground_loop_(electricity).
The following measures can be taken to minimise or eliminate these interferences:
A.Minimise all resistances (such as plugs, conductors) in the ground conductor of the signal.
B.Magnetic shielding of the sources of the impacting alternating magnetic fields.
C.Measures combining A and B
D.Separating the ground loop with the aid of (explosion-protected) isolating repeaters.