This standard is applicable to stationary or portable, single-phase or polyphase, air-cooled separating transformers, autotransformers, variable transformers and small reactors, associated or not, having a rated supply voltage not exceeding 1 000 V a.c., a rated frequency not exceeding 500 Hz, a rated no-load or load output voltage not exceeding 15 kV a.c. or d.c. and a rated output not exceeding: - single-phase transformers: 1 kVA - single-phase reactors: 2 kVAR polyphase transformers: 5 kVA - polyphase reactors: 10 kVAR unless otherwise specified in the relevant chapters. This standard is applicable to transformers where double or reinforced insulation between circuits is not required by the installation rules or by the appliance specification. The technological development of transformers might imply a need to increase the higher limit of the rated frequency. This standard is also applicable to transformers associated with specific items of equipment, to the extent decided upon by the relevant IEC Technical Committees. Normally, the transformers are intended to be associated with equipment to provide voltages different from the supply voltage for the functional requirement of the equipment. The safety insulation may be provided (or completed) by other features of the equipment, such as the body. Parts of output circuits may be connected to the input circuit or to protective earth. This standard is applicable to dry type or encapsulated transformers. For transformers filled with liquid dielectric or pulverized material, such as sand, requirements are under consideration.