Problems with the reliability of microprocessor-based protective devices (MPDs) have arisen in connection with the worldwide moving away from electromechanical and static protective relays to digital protective relays (DPRs). As shown in References 1 and 2, the common misconception that DPRs have reliability considerably exceeding that of electromechanical and static protective relays is, in actual fact, no more than a myth fostered through the years by the advertising publications of DPR manufacturers. It is abundantly clear that such complex multipurpose structures as DPRs cannot, even theoretically, be free of problems, cannot be absolutely reliable, and cannot be devoid of failure statistics during 15–20 years of maintenance.