IEC 61558-2-6:2021

Overview

IEC 61558-2-6:2021 is the IEC product safety standard for safety isolating transformers and power supply units (PSUs) incorporating safety isolating transformers for general applications. This third edition (2021) is a technical revision aligned with IEC 61558-1:2017, updating structure, references and symbols (including a new symbol for linearly regulated outputs). It is a Group Safety Publication (IEC Guide 104) and is to be used in conjunction with Part 1 (IEC 61558-1:2017).

Key scope points:

• Applies to stationary or portable, single- or polyphase, air-cooled dry-type transformers (natural or forced ventilation), with encapsulated or non-encapsulated windings.
• Rated supply voltage ≤ 1 000 V AC and frequencies (supply and internal) ≤ 500 Hz.
• Rated outputs normally limited to 10 kVA (single-phase) and 16 kVA (polyphase) unless agreed between purchaser and manufacturer.
• No-load output voltage ≤ 50 V AC or 120 V ripple‑free DC.
• Covers transformers incorporating electronic circuits and linear power supply units (switch‑mode PSUs are covered by IEC 61558-2-16).

Key Topics and Requirements

The standard supplements Part 1 with particular requirements and tests focused on safety isolation and practical use. Main technical topics include:

• Protection against electric shock and SELV requirements for isolated outputs.
• Ratings, classification and marking (including symbols and output voltage ratios).
• Electrical tests: insulation resistance, dielectric strength, leakage current.
• Thermal performance: heating, temperature rise and thermal protection.
• Short‑circuit and overload protection, short‑circuit voltage characteristics.
• Mechanical and environmental robustness: mechanical strength, ingress protection, resistance to rusting and external influences.
• Construction and components: internal wiring, terminals, earthing provisions, creepage and clearance distances, resistance to heat, fire and tracking.
• Special considerations for transformers with electronic circuits and power supplies with linear regulation.

Applications and Who Uses It

IEC 61558-2-6 is used by:

• Transformer and PSU manufacturers for design, testing and product compliance.
• Test laboratories and certification bodies performing safety assessments.
• OEMs and system integrators specifying safe isolating power sources for equipment.
• Regulatory and procurement teams ensuring compliance with SELV and isolation requirements. Typical applications include control circuits, SELV supplies, medical-adjacent equipment (where isolation is required by end-product standards), industrial control systems and other equipment needing double or reinforced insulation.

Related Standards

• IEC 61558-1:2017 (General requirements) - to be used together with this part.
• IEC 61558 series (other particular parts).
• IEC 61558-2-16 (switch-mode power supplies).
• Standards referenced for SELV and safety rules: IEC 61140, IEC 60364-4-41, and product/installation standards relevant to the end application.

Keywords: IEC 61558-2-6, safety isolating transformers, power supply units, transformer safety, SELV, IEC 61558-1:2017, transformer testing, linear power supply.