A ground loop forms when interconnected equipment is earthed at separate points, so any difference in earth potential, or a magnetic field linking the loop, drives current through cable screens and signal returns. In audio it is mains hum, in instrumentation offset and noise on 4 to 20 mA or thermocouple signals, and in data links errors. Fixes are single-point screen earthing, isolation amplifiers, fibre links and good bonding, never cutting the protective earth.
Hum disappears when you lift the screen at the field end, it's a ground loop between the control room and the cabinet.
Also heard as
- earth loop
Related terms
Common-mode
Describes signals or noise present equally, in the same phase, on both conductors of a pair relative to ground.
EMI
Electromagnetic interference: unwanted electrical noise that disturbs the operation of a circuit or system.
Equipotential bonding
Connecting metal parts together so they sit at one potential and no dangerous voltage appears between them.