Applies to stationary or portable single-phase or poly-phase air-cooled (natural or forced) independent or associated, isolating or safety isolating transformers intended for use on construction sites, having a rated supply voltage not exceeding 1 000 V a.c., and a rated frequency not exceeding 500 Hz. This part 2-23 is intended to be used in conjunction with IEC 61558-1. It has the status of a group safety publication in accordance with IEC Guide 104.