IEC 61558-2-8 Ed. 3.0 B:2024

This part of IEC 61558 deals with the safety of bell and chime transformers and power supply units incorporating bell and chime 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 bell and chime transformers and power supply units incorporating bell and chime 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 is applicable to stationary, single-phase, air-cooled (natural or forced) independent or associated dry-type transformers. The windings can be encapsulated or nonencapsulated.

The rated supply voltage does not exceed 250 V AC and the rated supply frequency and the internal operating frequencies do not exceed 500 Hz.

The rated output does not exceed 100 VA.

The no-load output voltage does not exceed 33 V AC or 46 V ripple-free DC, and the rated output voltage does not exceed 24 V AC, or 33 V ripple-free DC.

Bell and chime transformers are generally intended to supply domestic sound signalling equipment and other similar devices where the load is applied for short periods of time.

NOTE 2 A partial load can be applied for illumination purposes.

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.

NOTE 4 Normally the 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.

This document is applicable to transformers associated with specific equipment, to the extent decided upon by the relevant IEC technical committees.

Attention is drawn to the following, if necessary:
– 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.