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This part of IEC 61558 deals with the safety of transformers for class III handlamps and power supply units incorporating transformers for class III handlamps. Transformers incorporating electronic circuits are also covered by this document. NOTE 1 - Safety includes electrical, thermal and mechanical aspects. Unless otherwise specified, from here onward, the term transformer covers transformers for class III handlamps and power supply units incorporating transformers for class III handlamps. For power supply units (linear) this document is applicable. For switch mode power supply units IEC 61558-2-16 is applicable together with this document. Where two requirements are in conflict, the most severe take precedence. This document is applicable to stationary or portable, single-phase, air-cooled (natural or forced) independent or associated dry-type transformers. The windings can be encapsulated or non-encapsulated. The rated supply voltage does not exceed 1 000 V AC and the rated supply frequency and the internal operating frequencies do not exceed 500 Hz. Transformers have the following additional characteristics: − the no-load output voltage and the rated output voltage do not exceed 50 V AC or 120 V ripple-free DC; − there is only a small difference between the no-load output voltage and the rated output voltage. The rated output does not exceed 10 kVA. This document is not applicable to external circuits and their components intended to be connected to the input terminals and output terminals of the transformers. NOTE 3 - Transformers covered by this document are only used in applications where double or reinforced insulation between circuits is required by the installation rules or by the end product standard . Attention is drawn to the following, if necessary: − for transformers intended to be used in vehicles, on board ships, and aircraft, additional requirements (from other applicable standards, national rules, etc.); − measures to protect the enclosure and the components inside the enclosure against external influences such as fungus, vermin, termites, solar-radiation, and icing; − the different conditions for transportation, storage, and operation of the transformers; − additional requirements in accordance with other appropriate standards and national rules can be applicable to transformers intended for use in special environments.