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. Unless otherwise specified, from here onward, the term transformer covers bell and chime transformers and power supply units incorporating bell and chime 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 non-encapsulated. 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.
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