This Standard deals with all aspects of safety (such as electrical, thermal and mechanical) of: a) Stationary or portable, single-phase or polyphase, air-cooled (natural or forced) isolating and safety isolating transformers, associated or otherwise, having a rated supply voltage not exceeding 1 000 V a.c. and rated frequency not exceeding 1 MHz, b) Stationary or portable, single-phase or polyphase, air-cooled (natural or forced) separating transformers, auto-transformers, 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 1 MHz, a rated no-load or load output voltage not exceeding 15 kV a.c. or d.c., and for independent transformers not less than 50 V a.c. and/or 120 V ripple free d.c c) Power supply units incorporating a transformer of types a) or b).