Abstract
This paper describes cause and effect of an electrical arc fault in industrial TS 6/0.4 kV. Results of insulation resistance test, dielectric withstand test, thermographic inspection, testing of LV installation, as well as recorded data analysis are presented in detail and an events explanation is given. The aim of this paper is to show the purpose of complex testing, both during the events of the accident and during the preventive maintenance. It has also been recommended to analyse calculations of short-circuit currents and the effect of an electric arc on the staff in power facilities, the so-called “arc flash”.