A ground loop may occur when:

A ground loop can occur when a patient is connected to multiple diagnostic devices, each equipped with its own ground. This situation can create different ground potentials at each device, leading to unwanted signals or noise in the data being collected. In sleep study setups, for instance, if one device's ground reference is at a different potential compared to another, the connection points can form unwanted current loops. These currents can interfere with the measurements and result in artifacts, ultimately affecting the quality and accuracy of the recordings.

While grounding issues can occur with single devices or when electrodes are referenced to common ground points, the scenario described specifically highlights the complexities introduced when multiple devices are involved, making it a prominent situation for ground loops.