A ground loop is an electrical wiring problem where not all grounds are unified. Grounding is all relative, as it provides a reference point for measuring voltage potentials in a particular electrical system. Consider a computer power supply; measuring between the labeled ground and the +5V cable will read five volts on a meter, and between the ground and +12V cable, twelve volts. If the meter is instead connected directly to the +5V and +12V cables, it will read seven volts, because the +5V line in this isolated system is the ground, the zero-point to measure voltage from.

The problem of ground loops arises when two or more normally isolated systems are connected together and aren't using the same reference point for their grounds. This can arise from improperly connected components or faulty house wiring. Each system misinterprets the voltages from the other system, which can lead to feedback when dealing with audio components or visual interference on TVs. By using an isolation transformer, a 1:1 wrapping of insulated coils, a signal can be shared between two systems while electrically isolating them, keeping the ground loop from being a problem.