What defines a ground loop?

• A. A grounding loop is a simple shield path with no potential difference.
• B. A voltage differential existing between two grounding points.
• C. A loop used to physically connect grounds together.
• D. A voltage differential that exists between two different grounding points.

Answer: (D)

A ground loop happens when there are multiple grounding references in a system that are connected together, forming a closed conductive path, and those grounding points sit at different electrical potentials. The voltage difference between two distinct ground points drives current around the loop, which can flow through shields, chassis, or ground conductors and introduce hum or noise into the signal path.

That’s why the best description highlights a voltage differential that exists between two different grounding points. If the ground points are at the same potential, there isn’t a loop current to speak of, even if a loop physically exists. The other ideas miss the essential point: a loop by itself isn’t a problem unless there’s a voltage difference driving current through it.