This International Standard deals with all aspects of safety such as electrical, thermal and mechanical. This part 2-19 of IEC 61558 applies to stationary or portable, single-phase or poly-phase, air-cooled (natural or forced), independent or associated, isolating or safety isolating transformers, having a rated supply voltage not exceeding 1 000 V a.c., a rated frequency not exceeding 500 Hz, a rated output not exceeding 10 kVA. Perturbation attenuation transformers are intended to the supply of office machines and the like and have a mid-point lead out in the output circuit in order to attenuate mains borne disturbances. In addition, double or reinforced insulation between circuits required by the installation rules or by the appliance specification is fulfilled by using this transformer. This part 2-19 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.