IEC 61558-1:2017

Overview

IEC 61558-1:2017 - Safety of transformers, reactors, power supply units and combinations thereof (Part 1: General requirements and tests) is the third edition (technical revision) of the international safety standard for stationary and portable dry-type transformers, reactors and power supply units (including switch‑mode power supplies) that are not part of the distribution network. It replaces the 2005 edition and its 2009 amendment and is a group safety publication in accordance with IEC Guide 104. The 2017 edition (with corrigendum included) updates test methods, marking symbols and insulation requirements to reflect modern constructions and use cases.

Key topics and technical requirements

• Scope and classification: Safety requirements for dry‑type transformers, reactors and power supply units (encapsulated or non‑encapsulated windings), for both stationary and portable types.
• Electrical, thermal and mechanical safety: General requirements, protective earthing, touch current limits, insulation coordination and mechanical strength.
• Insulation and dielectric testing: New overvoltage categories (1–4) for clearances and dielectric strength tests; partial discharge testing introduced for fully insulated winding (FIW) constructions above 750 V.
• Winding and material requirements: Introduction of tests and tables for fully insulated winding (FIW) constructions and updated requirements for toroidal cores and division of basic/supplementary insulation.
• Temperature and ageing tests: Alternative temperature‑rise measurement and simulated load / back‑to‑back methods aligned with IEC 60076‑11; accelerated ageing provisions for undeclared insulation classes.
• Short‑circuit & overload: Updated short‑circuit and overload protection test methods (including simulated and back‑to‑back approaches per IEC 60076‑11).
• Mechanical & environmental tests: Increased emphasis on IP‑code modifications, vibration tests for vehicle and railway applications, tumbling barrel (pin‑damage) test for plug‑in PSUs, and symbols for minimum temperature and maximum altitude (>2 000 m).
• Components and connectors: Dimensioning rules for rectangular cross‑section connectors and updates to repetition dielectric testing (80% of required test voltage).

Practical applications and who uses the standard

IEC 61558-1:2017 is used by:

• Manufacturers and designers of transformers, reactors, and power supply units (including switch‑mode PSUs) to design safe products and prepare technical files for certification.
• Test laboratories and conformity assessment bodies for type and routine testing, dielectric and temperature‑rise verification, and mechanical/environmental testing.
• Safety engineers, product compliance managers and regulatory authorities assessing compliance with international safety requirements.
• Industries deploying transformers in industrial equipment, consumer electronics, railway and vehicle systems, and medical or control systems where safety isolation and performance under overload/fault conditions are critical.

Related standards

• IEC 60076‑11 (temperature and short‑circuit test methods for power transformers) - referenced for alternative test methods.
• IEC Guide 104 (group safety publications) and CENELEC Guide 29 (alignment on temperature adjustments).
• Other parts of the IEC 61558 series for specific product types and application‑specific requirements.

Keywords: IEC 61558-1:2017, transformer safety standard, power supply safety, dielectric strength, FIW, overvoltage categories, temperature‑rise test, transformer testing, IP-code, short‑circuit protection.