English: A schematic diagram showing one solution to the problem of a ground loop between electronic components - insert an isolation transformer in the signal cable. A ground loop is an inadvertent electrical circuit or loop created by the ground wiring of electrical equipment. Ground loops are a major cause of hum and interference in audio, video, and computer equipment, because circulating currents induced by stray magnetic fields from nearby 50/60 Hz equipment can cause AC voltage dropped across signal grounds. In this diagram two AC powered electronic components, C1 and C2, are connected by a shielded signal cable S. The ground shield of S, along with the ground wire ("third wire") P in the components' power cord and the building's utility ground wiring G form a ground loop.
One of the best ways to prevent such a ground loop is to insert an isolation transformer in the signal cable S, as shown. The transformer breaks the conductive path between the ground terminals of the components, opening the loop, preventing ground loop currents from flowing, while allowing the AC signal to pass. Unlike other solutions such as breaking the cable ground shield, the isolation transformer can be used with a "floating" component (one with no ground wire in its power cord) without causing hum. Cables incorporating isolation transformers can be purchased.