Editing Ground loop (electricity) (section)

==Representative circuit==
[[Image:Ground loop.svg|thumb|250px|Simplified circuit illustrating a ground loop]]

The [[circuit diagram]] illustrates a simple ground loop. Circuit 1 (left) and circuit 2 (right) share a common path to ground of resistance <math>\scriptstyle R_G</math>. Ideally, this ground conductor would have no resistance (<math>\scriptstyle R_G = 0</math>), yielding no voltage drop across it (<math>\scriptstyle V_G = 0</math>), keeping the connection point between the circuits at a constant ground potential. In that case, the output of circuit 2 is simply <math>\scriptstyle V_\text{out} = V_2</math>.

However, if this ground conductor has some resistance (<math>\scriptstyle R_G > 0</math>), then it forms a [[voltage divider]] with <math>\scriptstyle R_1</math>. As a result, if a [[Electric current|current]] (<math>\scriptstyle I_1</math>) is flowing through <math>\scriptstyle R_G</math> from circuit 1, then a voltage drop across <math>\scriptstyle R_G</math> of <math>\scriptstyle V_G\; =\; I_1 R_G</math> occurs, causing the shared ground connection to no longer be at the actual ground potential. This voltage across the ground conductor is applied to circuit 2 and added to its output:<math display="block">V_\text{out} = V_2 - V_G = V_2 - \frac{R_G}{R_G + R_1}V_1.\,</math>

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&nbsp;Hz hum in the speakers. Also, both circuits have voltage <math>\scriptstyle V_G</math> on their grounded parts that may be exposed to contact, possibly presenting a [[Electric shock|shock]] hazard.  This is true even if circuit 2 is turned off.

Although ground loops occur most often in the ground conductors of electrical equipment, similar loops can occur wherever two or more circuits share a common current path, which can cause a similar problematic voltage drop along the conductor if enough current flows.