UNE-EN IEC 61558-1:2021

This International Standard deals with safety aspects of transformers, reactors, power supply

units and combinations thereof such as electrical, thermal and mechanical safety.

This standard covers the following independent or associated stationary or portable types of

dry-type transformers, power supply units, including switch mode power supply units,

reactors and combinations thereof in the field of safety and EMF. The windings may be

encapsulated or non-encapsulated. They are not forming a part of the distribution network.

NOTE 1 The distinction between transformers, power supply units and switch mode power supply units 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 supply units, 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 supply units, 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 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 poly

phase 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 poly315

phase 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 2 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 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 3 Separating transformers are used where double or reinforced insulation between circuits is not

required by the installation rules or by the appliance specification.

NOTE 4 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 supply units and switch mode power supply units

incorporating one or more transformer(s) of type a) or b) 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 supply units not exceeding 500 Hz and for

switch mode power supply units not exceeding 100 MHz;

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