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