In this M.S. thesis, methods of technical diagnostics of squirrel-cage induction motors that are applicable to explosion-proof electric motor drives are described. The influence of hazardous area parameters on application of diagnostic methods is analysed, and also an analysis is given of special requirements for tests in the conditions of explosion hazard. Elements of explosion protection of electric motors designed in types of protection Flameproof enclosures - ”d”, Increased safety - ”e” and Pressurized - ”p” were tested in laboratory conditions. The tests and analyses were made in accordance with standards that are valid for explosion protection in the Republic of Croatia. The actions necessary to eliminate the detected defects are specified. The influence of frequency converters for feeding modern explosion-protected electric motor drives on parameters of the motor that are relevant in terms of explosion protection is considered. The condition of the squirrel cage and the dynamic eccentricity were tested on 1,9 MW and 500 kW motors with explosion protection type Increased safety - ”e”. The tests were made in operating conditions, applying the spectral analysis method to stator winding line current. The obtained results were used for assessment of the condition of rotor squirrel cage and the dynamic eccentricity, and also to define the necessary servicing activities and further periodic tests.