How It Works
The simplified circuit diagram on the right illustrates in principle how a ground loop works. Two circuits share a common wire connecting them to ground. Ideally the ground conductor should have no resistance, so the voltage drop across it, should be zero, keeping the point at which the circuits connect at a constant ground potential, isolating them from each other. In this case the output of circuit 2 is simply . However, if the ground conductor has significant resistance, it and will together form a voltage divider. As a result, if current of magnitude is flowing through from circuit 1, a voltage drop, across will occur and the ground connection of both circuits will no longer be at the actual ground potential. This voltage across the ground conductor will be applied to circuit 2 and added to the output:
Thus the two circuits are no longer isolated from each other, and circuit 1 can introduce interference into the output of circuit 2. If circuit 2 is an audio system, and circuit 1 has large AC currents flowing in it, the interference may be heard as a 50 or 60 Hz hum in the speakers. Also, both circuits will have voltage on their grounded parts that may be exposed to contact, possibly presenting a shock hazard. This is true even if circuit 2 is turned off.
Although they occur most often in the ground conductors of electrical equipment, ground loops can occur wherever two or more circuits share a common conductor or current path, if enough current is flowing to cause a significant voltage drop along the conductor.
Read more about this topic: Ground Loop (electricity)
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