This International Standard deals with safety aspects of power transformers, power supplies, reactors and similar products such as electrical, thermal and mechanical safety.

This standard covers the following types of dry-type transformers, power supplies, including switch mode power supplies, and reactors, the windings of which may be encapsulated or non-encapsulated :

NOTE 1 The distinction between transformers, power supplies and switch mode power supplies is as follows:

– for transformers, there is no change in frequency .However, transformers (e.g. constant voltage transformers) may have an internal resonance frequency not exceeding 30 kHz;

– for power supplies, the internal operational frequency and waveform are different from the supply frequency and waveform, and the internal operational frequency does not exceed 500 Hz (see definition 3.1.19);

– for switch mode power supplies, the internal operational frequency and waveform are different from the supply frequency and waveform and the internal operational frequency exceeds 500 Hz and does not exceed 100 MHz.

The relevant parts 2 may be found in the introduction of this standard.

a) Stationary or portable, single-phase or poly-phase, air-cooled (natural or forced), isolating and safety isolating transformers, independent or associated, not forming a part of distribution networks and with the following characteristics:

– rated supply voltage not exceeding 1 000 V a.c.;

– rated supply frequency not exceeding 500 Hz;

and complying with the following values, unless otherwise specified in the relevant part 2:

• for isolating transformers:

– rated output for single phase transformers, not exceeding 25 kVA, and for polyphase transformers not exceeding 40 kVA.

– no-load output voltage and the rated output voltage exceeding 50 V a.c., and not exceeding 500 V a.c, or 1 000 V a.c. to be in accordance with the National Wiring Rules or for a special application.

• for safety isolating transformers:

– rated output for single phase transformers not exceeding 10 kVA, and for polyphase transformers not exceeding 16 kVA.

– no-load output voltage and the rated output voltage not exceeding 50 V a.c. between conductors, or between any conductor and protective earth.

NOTE 1 Isolating and safety isolating transformers are used where double or reinforced insulation between circuits is required by the installation rules or by the appliance specification (for example toys, bells, portable tools, handlamps).

b) Stationary or portable, single-phase or polyphase, air-cooled (natural or forced) separating transformers, auto-transformers, variable transformers and small reactors, independent or associated, not forming a part of distribution networks and with the following characteristics:

– rated supply voltage not exceeding 1 000 V a.c.;

– rated supply frequency not exceeding 500 Hz;

and complying with the following values, unless otherwise specified in the relevant part 2:

– no-load output voltage or a rated output voltage for both independent and associated transformers not exceeding 15 kV a.c., and for independent transformers, a rated output voltage not less than 50 V a.c.;

– rated output not exceeding the following values:

– 1 kVA for single-phase transformers;

– 2 kVAR for single-phase reactors;

– 5 kVA for poly-phase transformers;

– 10 kVAR for poly-phase reactors.

NOTE 2 Separating transformers are used where double or reinforced insulation between circuits is not required by the installation rules or by the appliance specification.

NOTE 3 Normally, the transformers of type b) are intended to be associated with the 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 circuit or to the protective earth.

c) Stationary or portable, single-phase or polyphase, air-cooled (natural or forced), independent or associated power supplies and switch mode power supplies incorporating one or more transformer(s) of type a) or b), not forming a part of distribution networks and with the following characteristics:

– rated supply voltage not exceeding 1 000 V a.c.;

– rated supply frequency not exceeding 500 Hz;

– internal operational frequency for power supplies not exceeding 500 Hz and for switch mode power supplies not exceeding 100 MHz;

and with the following values, unless otherwise specified in the relevant part 2:

• for power supplies and switch mode power supplies incorporating isolating transformers:

– rated output for single- phase or polyphase power supplies or switch mode power supplies not exceeding 1 kVA;

– no-load output voltage and the rated output voltage exceeding 50 V a.c. or 120 V ripple- free d.c., and not exceeding 500 V a.c. or 708 V ripple- free d.c., or 1 000 V a.c. or 1 415 V ripple- free d.c. to be in accordance with national wiring rules or for a special application;

• for power supplies and switch mode power supplies incorporating safety isolating transformers:

– rated output for single- phase or polyphase power supplies and switch mode power supplies not exceeding 1 kVA;

– no-load output voltage and rated output voltage not exceeding 50 V a.c. or 120 V ripple- free d.c. between conductors, or between any conductor and protective earth.

NOTE 4 Power supplies and switch mode power supplies incorporating Isolating and safety isolating transformers are used where double or reinforced insulation between circuits is required by the installation rules or by the appliance specification (for example toys, bells, portable tools, handlamps).

• for power supplies and switch mode power supplies incorporating separating transformers, auto-transformers , and variable transformers:

– rated output for single-phase or polyphase power supplies and switch mode power supplies not exceeding 1 kVA;

– no-load output voltage and rated output voltage for both, independent and associated transformers not exceeding 15 kV a.c., and for independent transformers, a rated output voltage not less than 50 V a.c.;

NOTE 5 Power supplies and switch mode power supplies incorporating separating transformers are used where double or reinforced insulation between circuits is not required by the installation rules or by the appliance specification.

d) This standard is also applicable to t_w-marked transformers with a rated output not exceeding 1 000 VA and where the t_w-temperature does not exceed 140 °C (tw 140). However, t_w -marking of transformers is optional.

This standard also applies to transformers, power supplies, switch mode power supplies, and reactors incorporating electronic circuits.

This standard does not apply to external circuits and their components intended to be connected to the input and output terminals or socket-outlets of the transformers, power supplies and switch mode power supplies, and reactors.

NOTE 6 Attention is drawn to the following:

– for transformers intended to be used in vehicles, on board ships, and aircraft, additional requirements (from other applicable standards, National Rules, etc...) may be necessary;

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

– the different conditions for transportation, storage, and operation of the transformers 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 7 Future technological development of transformers may necessitate a need to increase the upper limit of the frequencies; until then this standard may be used as a guidance document.