English: Circuit diagram illustrating a ground loop. Two circuits share a common ground wire. The voltage of the ground connection, V_G, should ideally be zero. However if the ground conductor has significant resistance, R_G, the current flowing through it from circuit 1 will cause a voltage drop across it V_G = I₁R_G. Since they share the ground wire, this voltage appears as unwanted interference in the second circuit: V_out = V₂ + V_G.