IEC 61558-2-4:2009

Overview

IEC 61558-2-4:2009 is an international standard developed by the International Electrotechnical Commission (IEC) that specifies the safety requirements and tests for isolating transformers and power supply units incorporating isolating transformers used for general applications. The standard applies to products with supply voltages up to 1,100 V, covering both stationary and portable, single-phase or polyphase, air-cooled, dry-type transformers. It addresses transformers with or without electronic circuits, incorporating both encapsulated and non-encapsulated windings.

This second edition updates the requirements based on developments in IEC 61558-1 (2005) and reflects higher permissible supply voltages, ensuring harmonization with related standards and modern installation environments.

Key Topics

• Scope and Applicability

  • Applies to isolating transformers and power supply units for general use
  • Covers electrical, thermal, and mechanical safety aspects
  • Suitable for devices with rated output not exceeding 25 kVA (single-phase) or 40 kVA (polyphase)
  • Includes transformers with incorporated electronic circuits

• Safety Requirements

  • Double or reinforced insulation required between input and output circuits
  • Protection against electric shock, overload, mechanical stresses, moisture, and dust
  • Specific requirements for no-load and load output voltage ranges
  • Detailed marking and information requirements, including symbols for transformer type

• Testing and Compliance

  • Standardized testing procedures for electrical and mechanical safety
  • Tests for insulation resistance, dielectric strength, and leakage current
  • Output voltage and current measurements under various load and no-load conditions
  • Mechanical strength and resistance to environmental factors

• Construction and Marking

  • Mandatory separation of input and output circuits, and earth connections
  • Defined requirements for internal wiring, terminals, supply cables, and protective earthing provisions
  • Marking requirements include supply and output ratings, symbols, and compliance information

Applications

IEC 61558-2-4:2009 is essential for manufacturers and users of isolating transformers and associated power supply units in a variety of sectors:

• Industrial Equipment: Ensures safety in control panels, machine tools, and industrial automation systems
• Commercial Installations: Powers lighting systems, office equipment, and electronics requiring galvanic isolation
• Building Services: Used in lifts, medical operating rooms, and where isolation from mains supply is required
• Portable Power Supply Units: Guarantees safety and compliance in hand-held or mobile applications
• General Electrical Installations: Suitable where electrical isolation and safety barriers are necessary between input and output circuits

The standard helps reduce electrical hazards, supports the reliability of complex electronic systems, and assists compliance with both national and international regulations.

Related Standards

IEC 61558-2-4:2009 is part of the broader IEC 61558 series addressing the safety of transformers, reactors, and power supply units. Related standards include:

• IEC 61558-1: General requirements and tests for power transformers, power supplies, and reactors – this is the foundational standard used alongside Part 2-4.
• IEC 61558-2-16: Particular requirements and tests for switch mode power supply units and transformers for switch mode power supply units, relevant for applications utilizing switch-mode technology.
• IEC 60664-1: Touches on insulation coordination in low-voltage systems, referenced for clearances and creepage distances.
• IEC Guide 104: Guidelines for the preparation and use of safety publications.

Manufacturers and testing laboratories are strongly advised to use the latest editions of all related standards for full compliance and to ensure global acceptance of their products.

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