The protection of metal surfaces is crucial for the sustainable development of society. The need for as much metal as possible arises from day to day, and if we do not ensure proper protection of already existing metal structures, there can occur significant damage to the property as well as endangering the safety of people and the environment. The composition and application of organic coatings are of great importance in protecting metal surfaces from corrosion, but also the characterization and constant monitoring of the behavior of the coatings plays a major role. Electrochemical impedance spectroscopy (EIS) as a method based on alternating current does not impair the protective properties of the system and allows the characterization of the coating state by means of equivalent electrical circuits. In order to obtain correct results, it is important to pay attention to the influence of electromagnetic interference that act trought induction. Power lines or power sources are the most common sources of electromagnetic interferences that can affect the accuracy and precision of EIS measurements. In this study, the effect of increasing the amplitude of the input signal on EIS measurements under various leveles of interferencewas investigatedin laboratory and field conditions. Tests were performed on three simultaneous dummy cells with four electrical circuits of different combinations of capacitance and resistance. Laboratory tests were conducted under electromagnetically isolated conditions - Faraday's cage, field tests were conducted in the power substation, iclose to the AC traction rail and in the laboratory outside the Faraday cage.