BS EN IEC 61558-2-4:2025

Safety of transformers, reactors, power supply units and combinations thereof. Particular requirements and tests for isolating transformers and power supply units incorporating isolating transformers for general applications | Status: Current

1 Scope Replacement This part of IEC 61558 deals with the safety of isolating transformers for general applications and power supply units incorporating isolating transformers for general applications. 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 isolating transformers for general applications and power supply units incorporating isolating 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. 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 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 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.

The no-load output voltage or the rated output voltage does exceed 50 V AC or 120 V ripple-free DC, and where applicable, does not exceed 500 V AC or 708 V ripple-free DC. The no-load output voltage and the rated output voltage may be up to 1 000 V AC or 1 415 V ripple-free DC for special applications. 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 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:

• • 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 may 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 ISO/IEC 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.