In this article problems of design of interface devices within the computer sys- tems of railway automation using different element base are considered, the short review of modern products of leading vendors of small-sized power relays intended for printed mounting is given, also the principles of using of relays that are not de- vices of the first reliability class for design of safe circuits are considered. Particular attention is paid to methods of providing the necessary resource of relay switching circuits and relay’s application features for controlling high-voltage loads of direct current. Also the paper presents practical examples of implementation of safe in- terface devices using the small-sized power relays and considers the advantages of the proposed technical solutions in comparison with interface devices based on functional generators with asymmetrical failure.