# Insulation system > Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Insulation_system > Markdown URL: https://mediated.wiki/source/Insulation_system.md > Source: https://en.wikipedia.org/wiki/Insulation_system > Source revision: 1341527780 > License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) {{short description|System for classifying electrical insulation based on maximum safe operating temperature}} The '''electrical insulation system''' for [wire](/source/wire)s used in [generator](/source/Electric_generator)s, [electric motors](/source/electric_motors), [transformer](/source/transformer)s, and other wire-wound electrical components is divided into different classes by [temperature](/source/temperature) and temperature rise. The electrical insulation system is sometimes referred to as ''insulation class'' or ''thermal classification''. The different classes are defined by [NEMA](/source/NEMA),{{cite web|url=https://www.engineeringtoolbox.com/nema-insulation-classes-d_734.html|title=NEMA Insulation Classes|website=www.engineeringtoolbox.com}} [Underwriters Laboratories](/source/Underwriters_Laboratories) (UL),E. Alfredo Campo (ed.), ''Selection of polymeric materials: how to select design properties from different standards'' William Andrew, 2007 {{ISBN|0-8155-1551-0}} page 170 and [IEC](/source/International_Electrotechnical_Commission) standards. For complete electrically operated appliances, the "insulation system" is the overall design of electrical insulation of the energized components to ensure correct function of the device and protection of the user from [electric shock](/source/electric_shock). ==Temperature classes== {| class="wikitable" |- ! IEC 60085
Thermal class''International Electrotechnical Commission Standard 60085 Electrical Insulation- Thermal Evaluation and Designation'', 3rd edition, 2004, page 11 table 1 ! Old IEC 60085
Thermal class'''IEC 60085:2007 Table 1''' ! NEMA ClassNEMA standard MG-1 Motors and Generators ! NEMA/UL
Letter class ! Maximum hot spot
temperature allowed ! Relative thermal
endurance index (°C) ! Typical materials |- |90 || Y || || || 90 °C || >90 - 105||Unimpregnated paper, silk, cotton, vulcanized natural rubber, thermoplastics that soften above 90 °CM. A. Laughton, D. F. Warne (ed), ''Electrical engineer's reference book, 16th edition'' Newnes, 2003 {{ISBN|0-7506-4637-3}}, page 7-3 |- |105 || A || 105 || A || 105 °C || >105 - 120|| Organic materials such as [cotton](/source/cotton), [silk](/source/silk), [paper](/source/Electrical_insulation_paper), some synthetic fibersDonald G. Fink and Wayne H. Beaty (ed), ''Standard Handbook for Electrical Engineers, Eleventh Edition'', Mc Graw Hill, 1978, {{ISBN|0-07-020974-X}}, page 7-12 |- |120 || E || || || 120 °C || >120 - 130|| Polyurethane, epoxy resins, polyethylene terephthalate, and other materials that have shown usable lifetime at this temperature |- |130 || B || 130|| B || 130 °C || >130 - 155|| Inorganic materials such as mica, glass fibers, [asbestos](/source/asbestos), with high-temperature binders, or others with usable lifetime at this temperature |- |155 || F || 155|| F || 155 °C || >155 - 180|| Class 130 materials with binders stable at the higher temperature, or other materials with usable lifetime at this temperature |- |180 || H || 180|| H || 180 °C || >180 - 200|| Silicone elastomers, and Class 130 inorganic materials with high-temperature binders, or other materials with usable lifetime at this temperature |- |200 || N|| || N || 200 °C || >200 - 220|| As for Class B, and including [teflon](/source/teflon) |- |220 || R||220|| R || 220 °C || >220 - 250|| As for IEC class 200 |- | || || || S || 240 °C || || Polyimide enamel or Polyimide films |- |250 || || || || 250 °C || >250|| As for IEC class 200. Further IEC classes designated numerically at 25 °C increments. |} The maximum hot-spot [operating temperature](/source/operating_temperature) is reached by adding the rated ambient temperature of the machine (often 40 °C), a temperature rise, and a 10 °C hot-spot allowance. Electrical machines are usually designed with an average temperature below the rated hot-spot temperature to allow for acceptable life. Insulation does not suddenly fail if the hot-spot temperature is reached, but useful operating life declines rapidly; a rule of thumb is a halving of life for every 10 °C temperature increase. Older editions of standards listed materials to be used for the various temperature classes. Modern editions of standards are proscriptive, only indicating that the insulation system must provide acceptable life at the specified temperature rise. In large machines, different systems may be used according to the predicted temperature rise of the machine; for example, in large [hydroelectric](/source/hydroelectric) generators, stator windings may be Class B but the more difficult to cool rotor winding may be Class F. == Categories of insulation == In IEC standards, the insulation system is a classification based on the level of electrical shock protection given to a user. Functional insulation that is required to prevent short circuits within the equipment. Basic insulation is any material added to protect a user from accidental contact with energized parts. Supplemental insulation is rated to withstand 1500 volts AC. Double insulation is a design concept where failure of one insulation system will not expose the user to a shock hazard due to the presence of a second independent layer of insulation. Reinforced insulation is a supplemental insulation system that is strong enough to effectively perform as if a double insulation system was present. Selection of the insulation system is coordinated with the choice of [appliance class](/source/Appliance_classes).{{cite news |title= Understanding IEC Appliance Insulation Classes: I, II and III |url= http://www.fiduspower.com/news/understanding-iec-appliance-insulation-classes-i-ii-and-iii |work= Fidus Power |date= 6 July 2018 |access-date= 16 October 2018 |archive-date= 17 February 2020 |archive-url= https://web.archive.org/web/20200217041731/http://www.fiduspower.com/news/understanding-iec-appliance-insulation-classes-i-ii-and-iii |url-status= dead }} ==See also== * [Insulator (electricity)](/source/Insulator_(electricity)) * [Electrical insulation paper](/source/Electrical_insulation_paper) ==References== {{Reflist}} ==Further reading== * Greg Stone (ed.), ''Electrical insulation for rotating machines: design, evaluation, aging, testing, and repair'', Wiley-IEEE, 2004 {{ISBN|0-471-44506-1}} Category:NEMA standards Category:Electrical safety --- Adapted from the Wikipedia article [Insulation system](https://en.wikipedia.org/wiki/Insulation_system) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Insulation_system?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.