The book is intended for students as a textbook for theoretical and practical classes on the course of the same name . The book aims to give students the necessary theoretical understanding and the opportunity to prepare for practical classes included in the discipline program, while studying the section "Three-phase electrical circuits" . The content of the training manual includes issues of theory and practice of electrical safety calculations in three-phase networks. Methods of calculation of limit values of parameters of electric networks and grounding ensuring safety of electrical equipment and maintenance personnel, as well as methods of experimental estimation of parameters of isolation of networks in the existing electrical installations are given. The training manual is intended for students of higher educational institutions studying in the direction of "Agroengineering" in the framework of bachelor's training in the field of "Electrical equipment and electrical technologies in agriculture" and "Technical systems in agribusiness" . Can be recommended to students on the profile of "Power supply" and "Enterprise energy supply" . The publication is of interest to teachers, trainees of the system of advanced training and retraining of personnel .