Ground Loop Interference
We know that the body of electrical equipment should be grounded from electrical safety point of view. In case of power installations such a ground connection is achieved using a copper or iron rod which is driven into the ground to a depth of 10 to 100 feet below the surface. If one rod is insufficient, number of rods are used to achieve proper grounding. In any case, possible leakages and defects in the instrument should not produce a voltage more than 42 v between body of the equipment and ground.