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IEC 61558-2-8 2nd Edition, June 1, 2010
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Safety of transformers, reactors, power supply units and combinations thereof – Part 2-8: Particular requirements and tests for transformers and power supply units for bells and chimes
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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 standard.

NOTE 1 Safety includes electrical, thermal and mechanical aspects.

Unless otherwise specified, from here onward, the term transformer covers bell and chime transformers and This part of IEC 61558 deals with the safety of bell and chime transformers and power
 supply units incorporating bell and chime transformers. Transformers .

This part is applicable to stationary, single-phase, air-cooled (natural or forced) independent or associated dry-type transformers. The windings may be encapsulated or nonencapsulated.

This standard is applicable to transformers and power supply (linear).

This standard used in combination with part 2-16 for switch mode power supply (SMPS) units is also applicable to power supplies with internal operating frequencies higher than 500 Hz. Where the two requirements are in conflict, the most severe takes precedence.

The rated supply voltage does not exceed 250 V a.c., and the rated supply frequency and does not exceed 500 Hz. This standard is applicable to transformers and linear power supply units with internal operating frequency not exceeding 500 Hz.

The rated output shall not exceed 100 VA.

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

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 may be applied for illumination purposes.

This part is not applicable to external circuits and their components intended to be connected to the input terminals and output terminals of the transformers.

Transformers covered by this part are used only in applications where double or reinforced insulation between circuits is required by the installation rules or by the end product standard.

NOTE 3 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 may be provided (or completed) by other features of the equipment, such as the body. Parts of output circuits may be connected to the input circuits or to protective earth.

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

NOTE 4 Attention is drawn to the following:

- measures to protect the enclosure and the components inside the enclosure against external influences such as fungus, vermin, termites, solar-radiation, and icing should also be considered;

- the different conditions for transportation, storage, and operation of the transformer should also be considered;

- additional requirements in accordance with other appropriate standards and national rules may be applicable to transformers intended for use in special environments, such as tropical environment.

NOTE 5 Future technological development of transformers may necessitate a need to increase the upper limit of the frequencies, until then this part may be used as a guidance document.