EN IEC 61558-1, “Safety of transformers, reactors, power supply units and combinations thereof – Part 1: General requirements and tests”, sets the electrical, thermal and mechanical safety rules for small dry-type transformers and power supplies. It gives the general rules and is applied with the relevant part of the EN IEC 61558-2 series for the type of transformer. It is the basic standard for this product group in LVD testing.
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EN IEC 61558-1 at a glance
| Edition cited in the EU Official Journal | EN IEC 61558-1:2019 |
|---|---|
| Official title | Safety of transformers, reactors, power supply units and combinations thereof – Part 1: General requirements and tests |
| Legislation supported | Low Voltage Directive 2014/35/EU |
| Type of standard | Product standard |
Products covered
The standard covers dry-type transformers, reactors, power supply units and their combinations, whether sold on their own or built into other equipment. Typical examples:
- Isolating transformers
- Safety isolating transformers supplying extra-low voltage
- Control transformers
- Auto-transformers
- Switch mode power supply units and adapters
- Small reactors
Power transformers used in network distribution are outside this standard; they follow the EN 60076 series. For a transformer inside an appliance, the product standard of the appliance usually refers to this standard.
Main requirements of the standard
- Classification and ratings: Transformers are classified by protection class, type of short-circuit protection, IP rating and manner of use.
- Short-circuit and overload protection: Separate rules apply to inherently short-circuit proof, non-inherently short-circuit proof, non-short-circuit proof and fail-safe transformers.
- Protection against electric shock: Access to live parts is prevented; the insulation between input and output windings (basic, double or reinforced) depends on the type of transformer.
- Heating: The temperature of windings and other parts must stay within the limits for the thermal class of the insulation system.
- Insulation and dielectric strength: Insulation resistance and dielectric strength must be adequate after humidity conditioning.
- Construction: Rules are given for separation of windings, terminals, supply cords and earthing.
- Clearances and creepage distances: Clearance, creepage and distance through insulation depend on working voltage and pollution degree.
- Resistance to heat, fire and tracking: Insulating parts must resist heat, ignition and tracking.
- Marking: Ratings and the symbols showing the type of transformer appear on the product.
EN IEC 61558-1 tests
The tests are type tests on samples, carried out in the order given by the standard.
| Test or check | What is verified? |
|---|---|
| Output voltage and current | Output voltage on load and at no load agrees with the declared values |
| Heating test | Winding and surface temperatures stay within the permitted limits |
| Short-circuit and overload test | The transformer causes no hazard, according to its declared type of protection |
| Insulation resistance and dielectric strength | Insulation between windings and to the body is adequate |
| Mechanical strength | The enclosure withstands impact and stress; where needed, the IP degree of protection |
| Measurement of insulation distances | Clearances and creepage distances meet the required values |
| Heat and ignition tests | The insulating material resists heat and flame |
Its place in CE marking
- Risk assessment: Hazards are identified and the applicable standards selected.
- Design: The transformer is designed to EN IEC 61558-1 and the Part 2 for its type; the insulation system and the protection are fixed.
- Verification tests: Type tests are carried out on samples and reported.
- Technical file: Diagrams, the parts list and the test report go into the technical file.
- Declaration of conformity: EN IEC 61558-1 is listed among the standards applied and the CE marking is affixed.
Conformity with a harmonised standard gives presumption of conformity with the corresponding safety objectives of the Low Voltage Directive 2014/35/EU.
Standards applied together
- EN IEC 61558-2-4: Isolating transformers for general applications
- EN IEC 61558-2-6: Safety isolating transformers
- EN IEC 61558-2-16: Switch mode power supply units
- EN 61347-1: Lamp controlgear
- EN 62368-1: Audio/video and ICT equipment
- EN 61010-1: Measurement, control and laboratory equipment
Frequently asked questions
Is Part 1 enough on its own?
In most cases no. Part 1 gives the general rules and tests; the Part 2 for each type, such as isolating, safety isolating or switch mode units, adds its own rules and the two are applied together.
What is the difference between a safety isolating and an isolating transformer?
In both, input and output windings are separated by protective separation. A safety isolating transformer also supplies a safety extra-low voltage at its output.
Which edition applies?
The edition cited in the EU Official Journal under the Low Voltage Directive is EN IEC 61558-1:2019. Check the current citation before testing starts.
Other standards in this group
- EN 61439-2: Power Switchgear and Controlgear Assemblies
- EN IEC 62040-1: Uninterruptible Power Systems
- EN IEC 62031: LED Modules
- EN 61347-1: Lamp Controlgear
