The inverter-rectifier welding units MMA of the PROFESSIONAL series are designed for direct- current gas-shielded manual arc welding (MMA), argon-arc welding (TIG) and semi-automatic welding (MIG/MAG) as welding units with an external wire feeding unit. These welding units are designed for industry application. Due to the availability of additional adjustments, it is possible to set the optimal values of the unit parameters in various operating modes. The units ensure virtually continuous operation at rated currents 160 A, 200 A and 250 A. These currents are sufficient for manual arc welding with any electrodes from electrodes 1.6 mm in diameter through low-melting electrodes 6.0 mm in diameter, and for semi-automatic arc welding with solid welding wire 0.6 … 1.2 mm in diameter. The parameters of the welding unit are preset as optimal for the most operation modes. The more complex adjustment is possible, if required, provided that the welder has corresponding knowledge and experience. The welding units contains a module for protection against power supply overvoltage and undervoltage.