Harmonic Pollution It is usually the harmonic currents that are of concern, as they can cause “harmonic pollution” to spread to other equipment. Just like Current * Impedance = Voltage for fundamental frequency, Ohm’s Law also applies to harmonic current, impedance and voltage. Loads that draw current in a non-linear manner will cause harmonic-rich current to react with harmonic impedances and generate harmonic voltages that other loads will see. Harmonic impedances can change values with frequency or the harmonic number, often increasing significantly with the higher harmonics. This means that it will take less harmonic current to produce a significant harmonic voltage.