Posted on: July 1, 2014

A group loop is an unintentionally induced feedback loop caused by two or more circuits sharing a common electrical ground.

Ideally, all grounded points of an electrical system should be at the same potential. However different points of the same grounding system may have different potentials due to:

  • Variations in soil resistances
  • Distance separating the grounding conductors
  • Voltage and current transient voltages from lightening or heavy current loads
  • Facilities or buildings with faulty ground wiring

Ground loop is mostly formed in equipment installations consisting of multiple peripherals and devices connected to different power sources, and using the data lines, video or audio wires to communicate. If there is a difference between the various ground reference voltages, a current will flow from the higher reference ground point to a lower one through a circular path that uses the data line.

The current causes ground-loop induced voltages which may lead to unstable ground reference for the system. These are also a major source of noise and interference in electronic circuits such as video, sound and computer systems. The undesired noise degrades signals and may lead to data losses. In addition ground loop can create an electric shock hazard, and especially at the exposed metallic parts that are accessible to a user.

What is a ground loop

Symptoms of a ground loop

  • Equipment malfunction, intermittent lockups and computer glitches
  • Distorted video with dark bars, wavy lines, etc
  • Machine failure during lightening storms
  • Failure of a piece of the system or equipment may cause other parts to get damaged due to the ground loop

Eliminating ground Loops

Various connection methods and circuit designs are employed to reduce or avoid the occurrence of the ground loops.

  1. Connecting all physically connected devices to the same power outlet and ensure the grounded plugs are connected to the same circuit while un-grounded are used on another socket
  2. Running the equipment from the same circuit sharing a common ground
  3. Circuit design: The two common power supply designs are:
  • Floating output: This isolates the output voltage from the effects of the ground loops by having the line and neutral wires separated from the chassis ground of the sources. This is suitable for applications where interference from ground loops can damage sensitive electronic circuits or introduce errors in measurements equipment.
  • Grounded output: The neutral is grounded and tied to the source’s chassis ground. The chassis ground is also tied to the ground pin of the power source input. These are used in applications where the grounded neutral is required and also to comply with government regulations.