IEC 61558-2-2:2022

Overview

IEC 61558-2-2:2022 - "Safety of transformers, reactors, power supply units and combinations thereof - Part 2-2" - defines particular safety requirements and tests for control transformers and power supply units incorporating control transformers. This third edition (2022) replaces the 2007 edition, constitutes a technical revision and is published as a group safety publication (IEC Guide 104). It applies mainly to dry-type, air-cooled control transformers (including those with electronic circuits) used for control and safety extra-low-voltage (SELV) applications.

Key topics and requirements

The standard supplements IEC 61558-1:2017 and covers practical safety and test topics, including:

• Scope and classification - applicability to stationary/portable, single- or poly-phase devices; dry-type constructions; limits on voltages and frequencies.
• Rated limits - rated supply voltage ≤ 1 000 V AC and rated/internal frequency ≤ 500 Hz; no‑load or rated output voltage ≤ 1 000 V AC (or 1 415 V ripple‑free DC). Typical rated thermal output limits: 25 kVA (single-phase) and 40 kVA (polyphase), unless otherwise agreed.
• Electrical safety - protection against electric shock, insulation, creepage/clearance distances, dielectric strength, leakage current.
• Performance tests - output voltage/current under load, no-load voltage, short‑circuit voltage, short‑circuit and overload protection.
• Thermal and mechanical tests - heating, mechanical strength, resistance to fire/tracking and rusting.
• Construction and components - internal wiring, terminals, earthing provisions, components selection and marking.
• Ingress protection - protection against dust, solid objects and moisture.
• Specific symbols and markings - introduction of a new general symbol for control transformers and a new symbol for power supplies with linearly regulated outputs.
• Coordination with switch‑mode supplies - linear power supply units are covered here; switch‑mode power supplies are addressed by IEC 61558-2-16 in conjunction with this part - where requirements conflict, the more stringent applies.

Applications and who uses this standard

IEC 61558-2-2:2022 is used by:

• Transformer and power-supply manufacturers designing and marking control transformers and linear control PSUs.
• Product design and safety engineers ensuring compliance with electrical, thermal and mechanical safety requirements.
• Test laboratories and certification bodies performing safety and type tests.
• Procurement and compliance teams specifying safe control transformers for industrial control panels, machine tools, building automation, and SELV control circuits.
• Electrical installers and maintenance teams referencing safe limits and markings.

Related standards

• IEC 61558-1:2017 (general requirements)
• IEC 61558-2-16 (switch‑mode power supplies)
• IEC 60076-11 (other transformer types - excluded)
• SELV and control-circuit references: IEC 61140, IEC 60364-4-41, IEC 60204-1

This standard is essential for ensuring the safety, marking, testing and correct selection of control transformers and associated power supply units in industrial and control applications.