The paper provides a theoretical overview of electric resistance welding procedures with a more detailed description of the electric resistance spot welding procedure. The basic physical principle of electric resistance welding is described and the influence of key parameters on the quality of the welded joint is emphasized. Devices and types of electrodes used for electric resistance spot welding are mentioned. A process of the formation of a spot welded joint is described and its characteristic structure are mentioned. In the experimental part, the strips of sheets of various motor vehicle manufacturers (Opel, Peugeot and Toyota) are cut and in the longitudinal direction of the strip in four places by electric resistance spot welding are welded. After welding the strips, the sheets are cut off at the centre of the welded joint, suffused in the conductive mass, grinded and polished and a Metallographic analysis of the base sheet and welded sheets on the point of the spot welding joint are performed. After conducted discussion of the results of the metallographic tests, it was concluded that the portable spot welding device could achieve the microstructural characteristics of welded joints which are achieved by better devices with the possibilities of regulation of the input parameters