A distinction is made between single-phase and three-phase direct current with direct current welding units. With single-phase direct current, only one of the three phases is loaded, as a result of which an asymmetric network load is generated. With three-phase direct current, all three phases are loaded evenly, resulting in a symmetrical network load. Due to the rectification of the current as well as the specific construction of the welding portal, the current can only flow in a single direction. With direct current welding machines, the degree of efficiency lies at approx. 75% to 85%. The cross currents are minimised significantly as a result of the direct welding (reduced introduction of heat). This results in reduced welding currents, shorter welding times as well as an increased service life of the electrodes.