This International Standard applies to resistance welding equipment, to guns with inbuilt transformers and to complete movable welding equipment. The following types are included: — single-phase equipment with alternating welding current; — single-phase equipment with rectified welding current by rectification of the output of the welding transformer; — single-phase equipment with inverter welding transformer; — three-phase equipment with rectified welding current by rectification of the output of the welding transformer; — three-phase equipment with a current rectification in the input of the welding transformer (sometimes called frequency convertor); — three-phase equipment with inverter welding transformers. This International Standard applies neither to welding transformers sold separately nor to safety requirements.