UNE-EN IEC 61558-2-1:2026

Replacement

This document of the IEC 61558 series deals with safety of separating transformers for

general applications and power supply units incorporating separating transformers for

general applications. 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 separating

transformers for general applications and power supply units incorporating separating

transformers for general applications.

For power supply units (linear) IEC 61558-2-1 is applicable. For switch mode power

supply units, IEC 61558-2-16 is applicable.

IEC 61558-2-1 does not apply to transformers covered by IEC 60076-11.

IEC 61558-2-1 is applicable to stationary or portable, single-phase or polyphase, air-cooled

(natural or forced) independent or associated dry- type transformers. The windings may be

encapsulated or non-encapsulated.

The rated supply voltage does not exceed 1 000 V AC and the rated supply frequency and

the internal operating frequencies do not exceed 500 Hz.

The rated output does not exceed:

1 kVA for single-phase separating transformers and single-phase power supply units

incorporating separating transformers;

5 kVA for poly-phase separating transformers and poly-phase power supply units

incorporating separating transformers.

IEC 61558-2-1 is applicable to separating transformers without limitation of the rated

output subject to an agreement between the purchaser and the manufacturer.

NOTE 2 Transformers intended to supply distribution networks are not included in the scope.

The no-load output voltage or the rated output voltage does not exceed 1 000 V AC or

1 415 V ripple-free DC. For independent separating transformers and independent power

supply units, the no-load output voltage and / or the rated output voltage is not less than

50 V AC., or 120 V ripple-free DC.

IEC 61558-2-1 is not applicable to external circuits and their components intended to be

connected to the input terminals and output terminals of the transformers.

NOTE 3 Separating transformers covered by IEC 61558-2-1 are only used in applications where double or

reinforced insulation between circuits is not required by the installation rules or by the end product standard.

NOTE 4 Normally, the separating 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 earthing.

Attention is drawn to the following:

for separating transformers and power supply units incorporating separating

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 such as fungus, vermin , termites, solar-radiation, and icing should also be

considered;

the different conditions for transportation, storage, and operation of the separating

transformers and power supply units incorporating separating transformers should also

be considered;

additional requirements in accordance with other appropriate standards and national

rules may be applicable to separating transformers and power supply units incorporating

separating transformers intended for use in special environments, such as tropical

environment.

Future technological development of separating transformers and power supply units

incorporating separating transformers may necessitate a need to increase the upper limit of

the frequencies, until then IEC 61558-2-1 may be used as a guidance document.

This group safety publication is primarily intended to be used as a product safety standard for

the products mentioned in the scope, but shall also be used by technical committees in the

preparation of standards for products similar to those mentioned in the scope of this standard,

in accordance with the principles laid down in IEC Guide 104 and ISO/IEC Guide 51.

One of the responsibilities of a technical committee is, wherever applicable, to make use of

basic safety publications and/or group safety publications in the preparation of its

publications.