Cathodic protection (CP) is an electrochemical repair method for reinforced concrete (RC) structures. It has been subject to numerous research projects and has proven its capabilities in countless repair measures around the world. Nevertheless, due to the uniqueness of each application as well as the large number of influencing factors (e.g., geometry, concrete resistivity distribution, kinetics of rebar, and CP anode system) the design and operation of CP systems is still governed by the use of (semi‐) empirical calculations and criteria. Within this study, numerical simulation has been used to determine the current and potential distribution during the application of CP. On the basis of this data, which are not measurable on site, the significance of the most important criterion for the operation of CP systems, the so called 100 mV decay criterion, shall be discussed. In particular, the correlation of the criterion with the corrosion state of the active reinforcement against a backdrop of time dependent effects of CP is within the scope of this study.