The book discusses calculations of short-circuit currents, the choice of equipment, protections and cables in electrical networks of 0.4 kV power plants and substations of power systems, industrial and agricultural enterprises. References required for calculations are given. The issues of emergency power supply, long-range redundancy of failures of protections and circuit breakers and the use of digital equipment in networks of this voltage are considered. Designed for employees of design organizations and for personnel serving electrical networks.