ISO 669:2016 defines and specifies certain identified electrical and mechanical characteristics of equipment used for - resistance spot welding, - projection welding, - resistance seam welding, - upset welding[1], and ? flash welding[2]. ISO 669:2016 specifies the information to be given in equipment specifications and the test methods to be used for measuring those characteristics. Not all requirements apply to all types of equipment. The following types of power sources are included: - single phase with alternating welding current; - single phase with rectified welding current by rectification of the output of the welding transformer; - single phase with inverter welding transformer; - three phase with rectified welding current by rectification of the output of the welding transformer; - three phase with a current rectification in the input of the welding transformer (sometimes called frequency convertor); - three phase with inverter welding transformers. ISO 669:2016 Standard does not apply to welding transformers that are separate from the equipment. NOTE Safety requirements for resistance welding equipment are covered by IEC 62135?1. [1] Often referred to by the non-preferred term, butt welding. [2] Often referred to by the non-preferred term, flash butt welding.