This part of IEC 61558 deals with the safety of control transformers and power supply units incorporating control transformers. 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 control transformers and power supply units incorporating control transformers.

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 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.

The rated thermal output does not exceed:
• 25 kVA for single-phase transformers,
• 40 kVA for polyphase transformers.
This document is applicable to transformers without limitation of the rated thermal output, subject to an agreement between the purchaser and the manufacturer.

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

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 transformers the no-load output voltage and / or the rated output voltage is not less than 50 V AC or 120 V ripple-free DC.

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 not required by the installation rules or by the end product standard.

NOTE 4 Normally the control transformers are intended to be used 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 input circuits or to protective earthing.

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.

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 technical committees 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 technical committee is, wherever applicable, to make use of basic safety publications and/or group safety publications in the preparation of its publications.