Harmonic currents propagate throughout power and grounding systems and subtly corrupt electronic signal-circuit operations. In digital equipment, higher error rates appear. In a recording studio, these undesirable elements may appear as hum or a buzz or perhaps an overall muddy sound. Reactive currents that propagate throughout the grounding system are at the heart of the matter. Though non-linear or reactive loads are frequently blamed as the source of these problems, it has been found that conventional AC wiring methods are largely responsible for propagating this local interference.
Reactive currents resulting from non-linear loading are a simple law of physics.
Unbalanced power provides the means by which common harmonic and reactive currents build up on neutral wires and grounding circuits. Once in the ground reference, these trickled artifacts invade signal circuitry and contaminate program material. Sometimes engineers will try to lower the impedance of the grounding system to reduce noise, but this has little effect on reactive current in the ground. The grounding reference appears to be the noise source. Whenever hum or hum bars are observed, reactive power has invaded the grounding system.