The first part describes the basic parts and types of uninterruptible power supplies. More specifically, the concept of the uninterruptible DC grid is described, describing the topologies, working patterns, and analyzed items that need to be analyzed when designing uninterruptible DC grids. In the next part, the paper discusses the components of the uninterruptible DC distribution system, in order to provide an insight into the dimensioning and selection of equipment. Different types of batteries are described especially VRLA and Ni-Cd battery packs are compared as most commonly used batteries. The types of loads and their key characteristic and performance are processed. In addition, it deals with switching and switchgear and electrical protective equipment, which also describes types and defines characteristic sizes that are essential for design selection. As an essential condition of the gear selection, the selectivity of the protective devices to be satisfied in order to ensure safe operation of the system. In the last part of the thesis, on the example of a substation, the gradual process of calculation and dimensioning of the 220V DC grid. In which the concept of divorce was analyzed and a review of loads as basic parameters for further calculation. The voltage drop conditions and the battery discharge current check are performed. The converter is dimensioned, then short-circuit and the voltage drops are calculated after which the selectivity of the protection is determined.