This part of IEC 61558 deals with the safety of variable transformers for general applications and power supply units incorporating variable transformers for general applications. Transformers incorporating electronic circuits are also covered by this document.

NOTE 1 Safety includes electrical, thermal, mechanical and chemical aspects.

Unless otherwise specified, from here onward, the term transformer covers variable transformers for general applications and power supply units incorporating variable transformers for general applications.

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 does not apply to transformers covered by IEC 60076-11.

This document is applicable to stationary or portable, single-phase or polyphase, air-cooled (natural or forced) independent or associated variable dry-type transformers:
- variable auto-transformers;
- variable separating transformers;
- variable isolating transformers;
- variable safety isolating 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 operational frequencies do not exceed 500 Hz.

The rated output does not exceed:
- 40 kVA for single-phase variable auto-transformers;
- 200 kVA for polyphase variable auto-transformers;
- 1 kVA for single-phase variable separating transformers;
- 5 kVA for polyphase variable separating transformers;
- 25 kVA for single-phase variable isolating transformers;
- 40 kVA for polyphase variable isolating transformers;
- 10 kVA for single-phase variable safety isolating transformers;
- 16 kVA for polyphase variable safety isolating transformers.

This document is applicable to variable transformers without limitation of the rated output subject to an agreement between the purchaser and the manufacturer.

NOTE 2 Transformers intended to supply distribution networks are not included in the scope.

For variable auto-transformers:
- the no-load output voltage or the rated output voltage does not exceed 1 000 V AC or 1 415 V ripple-free DC;
- for independent variable auto-transformers the rated output voltage does exceed 50 V AC or 120 V ripple-free DC but does not exceed 250 V AC.

NOTE 3 Normally, variable auto-transformers are intended to be associated with equipment to provide voltages different from the supply voltage for the functional requirements of the equipment. The protection against electric shock can be provided or completed by other features of the equipment, such as the body.

NOTE 4 Variable auto-transformers intended to be used by technically skilled or trained personnel are considered as associated variable transformers and can have a rated output voltage less than 50 V AC.

For variable separating transformers:
- the no-load output voltage or the rated output voltage does not exceed 1 000 V AC or 1 415 V ripple-free DC;
- for portable variable separating transformers the rated output voltage does exceed 50 V AC or 120 V ripple-free DC;
- are only used where double or reinforced insulation between circuits is not required by the installation rules or by the end product standard.

NOTE 5 Normally, variable separating transformers are intended to be associated with equipment to provide voltages different from the supply voltage for the functional requirements of the equipment. The protection against electric shock can be provided or completed by other features of the equipment, such as the body. Parts of output circuits can be connected to the protective earthing.

NOTE 6 Variable separating transformers intended to be used by technically skilled or trained personnel are considered as associated variable transformers and can have a rated output voltage less than 50 V AC or 120 V ripple-free DC.

For variable isolating transformers:
- the no-load output voltage or the rated output voltage does not exceed 500 V AC or 708 V ripple-free DC. The no-load output voltage and the rated output voltage can be up to 1 000 V AC or 1 415 V ripple-free DC for special applications or in accordance with the installation rules;
- for independent variable isolating transformers the rated output voltage does not exceed 250 V AC;
- are used where double or reinforced insulation between circuits is required by the installation rules or by the end product standard.

For variable safety isolating transformers:
- the no-load output voltage or the rated output voltage does not exceed 50 V AC or 120 V ripple-free DC;
- are used where double or reinforced insulation between circuits is required by the installation rules or by the end product standard.

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.

Attention is drawn to the following, if necessary:
- additional requirements for transformers intended to be used in vehicles, on board ships, and aircraft, (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.

Future technological development of transformers can necessitate a need to increase the upper limit of the frequencies. Until then this document can be used as a guidance document.

This group safety publication focusing on safety guidance is primarily intended to be used as a product safety standard for the products mentioned in the scope, but is also intended to be used by TCs in the preparation of publications for products similar to those mentioned in the scope of this group safety publication, in accordance with the principles laid down in IEC Guide 104 and lSO/lEC Guide 51.

One of the responsibilities of a TC is, wherever applicable, to make use of BSPs and/or GSPs in the preparation of its publications.