IEC 60085 is an international standard that defines the thermal classification of electrical insulation systems. The standard specifies permissible continuous operating temperatures at which electrical insulating materials and insulation systems retain their functional properties over a defined service life.
IEC 60085 is a fundamental reference standard in electrical engineering, particularly for electric motors, generators, transformers, chokes and electrical equipment. The standard is used worldwide for the design, evaluation and comparability of insulation systems.
Technical Properties and Fundamentals
Purpose and Scope of IEC 60085
IEC 60085 specifies:
- Thermal classes for electrical insulating materials and insulation systems
- Maximum permissible continuous temperatures
- Uniform designations for thermal classes
The standard applies to electrical insulating materials, insulating components and complete insulation systems. IEC 60085 makes no statements on electrical dielectric strength or mechanical properties.
The Concept of the Thermal Class
A thermal class describes the maximum permissible temperature at which an insulation system can be operated over an economically defined service life. The service life is thermally limited and is based on ageing mechanisms such as oxidation, polymer degradation or embrittlement.
The thermal class is not an instantaneous value but a continuous operating value.
Thermal Classes according to IEC 60085
Overview of the Standardised Thermal Classes
IEC 60085 defines the following thermal classes:
| Thermal class | Maximum continuous temperature |
|---|---|
| Y | 90 °C |
| A | 105 °C |
| E | 120 °C |
| B | 130 °C |
| F | 155 °C |
| H | 180 °C |
| N | 200 °C |
| R | 220 °C |
| S | 240 °C |
These values represent the maximum continuous temperature of the insulation system.
Relevance for Insulation Systems
An insulation system is always considered as a whole. The thermal class of the system is determined by its thermally weakest component. Individual insulating materials with higher temperature resistance do not automatically raise the system class.
Insulating Material versus Insulation System
Insulating Materials
Insulating materials are individual materials such as films, papers, varnishes or resins. Their thermal classification is based on material-specific tests or manufacturer data.
IEC 60085 itself does not classify individual products but provides the reference system for their categorisation.
Insulation Systems
An insulation system consists of several insulating materials in a defined combination and processing. The thermal class of a system is determined through system tests or empirical values.
The standard explicitly distinguishes between material properties and system behaviour.
Application in Practice
Electric Motors and Generators
IEC 60085 is frequently used to specify the thermal class of winding insulation systems. Typical classes are F and H. The thermal class influences:
- Permissible winding temperature
- Power density
- Service life
Transformers and Chokes
In transformers, too, IEC 60085 serves as a reference for the thermal design of insulation systems. The operating temperature results from losses, cooling and ambient conditions.
Influence on Design and Purchasing
Specifying the thermal class is a key criterion in:
- Material selection
- Supplier selection
- Comparison of insulation systems
- Quality assurance
Distinction from Related Standards
IEC 60085 is a basic standard. It does not replace product-specific or machine-specific standards. Other standards govern:
- Test methods
- Service life determination
- Safety requirements
The thermal class according to IEC 60085 must always be considered in the context of the respective product standard. A practical overview is also provided in the article on insulation material classes.
Limits of IEC 60085
IEC 60085 makes no statements on:
- Short-term overtemperatures
- Electrical dielectric withstand strength
- Mechanical load capacity
- Environmental conditions such as humidity or chemicals
The standard exclusively describes thermal classification.
GOBA Takeaway
IEC 60085 is the central reference standard for thermal classes of electrical insulation systems. The standard creates a uniform basis for evaluating the thermal load capacity of insulation systems in electrical engineering.
For design, manufacturing and purchasing, the correct interpretation of the thermal class is decisive. The actual performance always results from the complete insulation system and the real operating conditions.