A ground loop is the name for the current return paths of any number devices connected to the same ground reference. However, since large or high-current ground loops are also common sources of noise, the term ground loop more commonly refers to ground loop interference. Ground loop interference happens when components drive large currents through the system ground. The resulting current fluctuations on the ground bus, which has a limited impedance, creates a potential difference between local grounds. We consider the resulting ground potential difference (GPD) between local grounds and the system ground to be ground loop interference.

The ground potential difference shown in #FIG_Y2D_VXB_TVB can range anywhere from a few milli-volts to the kilo-volt range depending on the application, and can create a range of undesirable effects. They can be as mild as digital communication errors and analog signal interference or as severe as a hazard of electrical shock that can harm instruments and operators. Many designers have to take into consideration the effects that ground loops can have on their end equipment. Industrial motor drives, power supplies, amplifiers, and vehicle alternators are all common applications that can produce switching noise or high currents that can cause ground loop interference if not properly accounted for.

Audio applications often suffer from similar ground loop problems. Here, ground loops are often created when connecting parts of the audio system using a shielded grounded cable, and can manifest as a hiss, whine, or hum that interferes with the signal within the audio signal range.