Industrial Electrical Insulation

Orientation for industrial electrical insulation materials: assembly stage, grade and form distinctions, evidence to request. Safety-critical: specialist review required.

Buyer summary

What it is: Insulating films, papers, laminates, tapes and composites used in electrical equipment. This is a safety-critical choice that belongs to a qualified engineer.
Main applications: Transformer windings and cores, motor slot liners and phase separators, switchgear barriers, busbar wrapping, cable tapes, capacitor films, battery packs and power electronics.
Critical purchasing specifications: Voltage, thermal class and the equipment standard
Dielectric strength with the procedure used (ASTM D149)
Tracking resistance (CTI) and flammability
Short-term versus continuous temperature, stated separately
Listing evidence where claimed (for example a UL file)
Qualification considerations: A material's thermal class cannot be applied to an insulation system without proof (IEC 60085). Short-term heat resistance is not a thermal class.
First step: Have your engineer state the voltage, the thermal class, the construction and the certification requirements.
How PAXOMER can assist: Electrical insulation must be selected by a qualified engineer against documented test data. PAXOMER can help assemble the voltage, thermal class, construction and certification requirements as a written brief, identify manufacturers able to document them, and coordinate samples for your own testing. Commercial discussions follow only after the documentation route is clear. Manufacturer identification, qualification support and pricing discussions depend on manufacturer confirmation, specifications, quantities and terms.

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Detailed technical guidance, data tables, FAQs and technical references follow below.

Safety-critical electrical material. Insulation and winding materials must be selected by a qualified electrical engineer against documented test data and, where required, an evaluated insulation system. Material thermal class, short-term temperature survival and system approval are different things. Nothing here selects or qualifies a material.

General technical information published by PAXOMER Inc. to support preliminary material evaluation. It is compiled from the sources cited on this page and has not been independently reviewed or certified by a professional engineer, laboratory or certification body. Values marked typical, illustrative or requiring confirmation are not specifications. Confirm properties, standard editions, regulatory status and suitability for your specific application with the manufacturer and, where the use is regulated or safety-related, with a qualified professional or the relevant authority.

Electrical insulation materials separate conductors from each other and from earth: films, papers, pressboard, laminates, tapes, sleeving and varnish-impregnated structures used in transformers, motors, switchgear, cables, capacitors and busbar systems. Selection is a safety-critical engineering decision. A material’s dielectric strength, thermal class or tracking resistance describes the material under defined test conditions; it does not qualify the material for a particular electrical system, which depends on voltage, frequency, temperature, humidity, contamination, mechanical stress, ageing and the other materials in the insulation system.

This page is general technical orientation to help buyers and engineers ask better questions. It explains the vocabulary and test methods, shows how thermal class and dielectric strength are defined in the sources read, and sets out what evidence to request. It does not select, size or qualify any insulation. A qualified electrical engineer and documented test data decide, and a generic material must never be assumed qualified for a specific system. PAXOMER does not state that it stocks, represents or has qualified any insulation material.

A. Product identity and terminology

1. What does electrical insulation do?

It prevents unwanted current paths, withstands the voltage stress between conductors, and often provides mechanical support, spacing and thermal management. Materials are chosen as part of an insulation system: conductor, enamel or film, tapes, papers or laminates, varnish or resin, and the surrounding medium such as air, oil or gas. Related polymer-film and adhesive-tape topics appear in the guide Industrial material specification and supplier qualification checklist; this page concentrates on the insulation questions.

2. Which four temperature and approval concepts must be kept apart?

Four concepts that are often confused
Concept	What it means	Where the evidence comes from
Material thermal class	A designation of the maximum use temperature for which a material or system is appropriate under defined ageing criteria	Thermal evaluation according to the classification standard (IEC 60085 and the IEC 60216 ageing methods it relies on) or a listing such as a UL relative thermal index
Short-term temperature survival	How long a material tolerates a higher temperature (for example minutes during soldering or overload)	Manufacturer test statements for the exact product; usually much higher than the class temperature and not a substitute for it
Insulation system approval	Evidence that the combination of materials in a motor, transformer or device performs at a given class	System evaluation of the specific construction; a material's class cannot be applied to a system without that proof
Specific grade performance	Dielectric, mechanical and thermal values for one product and thickness	That manufacturer's current data sheet, with test method, conditioning and edition; typical values are not specification limits

This page keeps these apart. Short-term figures quoted below come from one tape maker's explanatory page and are labelled as such; grade values come from one aramid-paper data sheet and apply only to that product.

3. Which material families are used?

Insulation material families and points to confirm
Family	Reported features	Points to confirm
Polyester (PET) film and tape	Common insulating film. Short-term exposure example from one tape maker (not a thermal class): roughly 220 °C for 30 minutes (S2)	Continuous thermal class; thickness; adhesive
Polyimide film	Short-term exposure example from one tape maker (not a thermal class): about 400 °C for one hour (S2)	Continuous rating; adhesive; cost
Aramid paper (for example Nomex type 410)	Eleven thicknesses 0.05–0.76 mm; UL-recognised at 220 °C; full data sheet read (S5)	Values are averages, not specification limits; check the grade and your system
Cellulose paper and pressboard	Traditional transformer insulation, usually oil-impregnated	Moisture content; impregnation; ageing
Laminates and composites	Resin-bonded fibre layers for structural insulation	Resin system; thermal class; tracking
Varnishes, resins, tapes	Impregnation and wrapping	Compatibility with enamel and other plastics

Source basis: S2, S5 (one product); other rows are general descriptions without cited data.

4. Where are insulation materials used?

Transformer windings and cores, motor slot liners and phase separators, switchgear barriers and supports, busbar wrapping, cable tapes, capacitor films, battery packs and power electronics. Each use has its own standards and the choice belongs to the equipment designer.

5. When is a material suitable, and when not?

Reasonable candidates: materials with a documented thermal class and dielectric data under the conditions of the application, tested as part of the insulation system or accepted by the equipment standard.

Weak candidates: a material with only a general-purpose data sheet, a system change (for example a new varnish or tape) without re-evaluation, or a material chosen only for its room-temperature breakdown voltage when humidity, contamination or ageing govern.

6. Which terms will I meet?

Dielectric strength, breakdown voltage, partial discharge, thermal class, relative thermal endurance (RTE), insulation system, tracking, comparative tracking index (CTI), proof tracking index (PTI), performance level category (PLC), flashover, puncture, creepage and clearance, impregnation, UL 1446, IEC 60085, IEC 60216, ASTM D149. Glossary: density.

B. Properties and performance

7. What is a thermal class?

A catalogue listing of IEC 60085:2004 says a thermal class designates an insulating material or system by the numerical value of the maximum used temperature in °C for which it is appropriate, based on relative thermal endurance (RTE) against a control of known service performance. Its Table 1 lists classes 70, 90, 105, 120, 130, 155, 180, 200, 220 and 250, with the former letter classes Y, A, E, B, F and H. The listing’s status fields conflict (it shows the 2004 edition as published but also as deleted, with a 2007 revision), so the current edition must be checked (S1). A tape maker’s page lists the same letters with maximum temperatures and UL 1446 equivalents, and notes inconsistent entries for the top class (S2).

Thermal classes as listed

From an IEC 60085:2004 catalogue listing and a tape maker's table. The listing's status is internally inconsistent and the tape table has an inconsistent top-class entry. Not material data.

Thermal classes as listed
Property	Value or range	Unit	Test conditions	Test method	Grade or construction	Source	Verification status
Class Y (class 90)	90	°C	Maximum used temperature	IEC 60085	Classification label	S1, S2	Confirm against the cited standard or source
Class A (class 105)	105	°C	Maximum used temperature	IEC 60085	Classification label	S1, S2	Confirm against the cited standard or source
Class E (class 120)	120	°C	Maximum used temperature	IEC 60085	Classification label	S1, S2	Confirm against the cited standard or source
Class B (class 130)	130	°C	Maximum used temperature	IEC 60085	Classification label	S1, S2	Confirm against the cited standard or source
Class F (class 155)	155	°C	Maximum used temperature	IEC 60085	Classification label	S1, S2	Confirm against the cited standard or source
Class H (class 180)	180	°C	Maximum used temperature	IEC 60085	Classification label	S1, S2	Confirm against the cited standard or source
Class 200	200	°C	Maximum used temperature	IEC 60085	Classification label	S1, S2	Confirm against the cited standard or source
Class 220	220	°C	Maximum used temperature	IEC 60085	Classification label	S1, S2	Confirm against the cited standard or source
Class 250	250	°C	One tape-maker table lists 240 for this class; confirm against the current IEC 60085 edition	IEC 60085	Classification label	S1, S2, S7	Confirm against the cited standard or source

8. What does a thermal class not tell me?

A tape maker’s page states the heat classes give no information on maximum short-term load temperature, which is usually much higher, citing polyester at about 220 °C for 30 minutes and polyimide at about 400 °C for one hour as examples, and describes a classification criterion in which breakdown voltage must remain at 50% of the initial value after 20,000 hours at maximum operating temperature (S2). IEC 60085, per the listing, also says a material’s class cannot be applied to a system containing it without proof (S1). A thermal class is therefore a starting point for ageing, not a statement about a particular device. A UL relative thermal index such as the 220 °C quoted for one aramid paper (S5) is a rating of the material in the UL programme; it is not an IEC 60085 system class.

9. How is dielectric strength tested, and how should it be read?

ASTM D149-25 (active, last updated September 2025 on the store listing) covers procedures for the dielectric strength of solid insulating materials, mostly through-thickness puncture and also flashover. It has three voltage-application methods (A short-time, B step-by-step, C slow rate-of-rise); a default frequency of 60 Hz and suitability from 25 to 800 Hz; and states it is not for intrinsic or DC dielectric strength or thermal failure. Results rarely predict behaviour in an actual application directly. A citing document must specify method, specimen preparation, medium, temperature and electrodes, so a figure without these conditions is not comparable. The method is similar to IEC 60243-1 (S3). The value in kV/mm also depends strongly on thickness, so compare like thicknesses only.

Dielectric strength test parameters

From the ASTM D149-25 store listing. Describes the test method; contains no material values.

Dielectric strength test parameters
Property	Value or range	Unit	Test conditions	Test method	Grade or construction	Source	Verification status
Voltage application method A	short-time	not applicable	Voltage raised at a uniform rate	ASTM D149	Test procedure	S3	Verified reference value (published source)
Voltage application method B	step-by-step	not applicable	Stepped voltage	ASTM D149	Test procedure	S3	Verified reference value (published source)
Voltage application method C	slow rate-of-rise	not applicable	Slower ramp	ASTM D149	Test procedure	S3	Verified reference value (published source)
Default test frequency	60	Hz	Suitable 25–800 Hz	ASTM D149	Test procedure	S3	Verified reference value (published source)

10. What is tracking resistance?

Tracking is the formation of a conductive carbonised path along an insulator surface. A 3M technical brief on its tapes describes the IEC-based comparative tracking index (CTI) test: a drop of 0.1% ammonium chloride electrolyte every 30 seconds, ending after 50 drops or when tracking occurs, on a 3 mm specimen (tapes are stacked to thickness), at up to 600 V; on a failure the voltage is typically lowered by 25 V and the test repeated, the passing voltage must hold at five sites and a further 100 drops at 25 V lower, and both sides of a tape are tested. It cites IEC 60112, 4th edition (2003), and gives material groups I (CTI 600 or above), II (400 to below 600), IIIa (175 to below 400) and IIIb (100 to below 175, eliminated after 2008); higher CTI permits smaller creepage distances; and the values on that page are 3M’s own testing, with UL verification of a subset (S6). An encyclopaedia article gives the performance level categories PLC 0 to 5 used in UL 746A (S4), the scheme under which the Nomex data sheet reports category 3 (S5). Electrode spacing was not stated in either source and should be taken from IEC 60112.

Tracking classification as cited

Performance levels from an encyclopaedia article; material groups from a 3M technical brief citing UL 1950 and IEC 60112. The standards were not read. Not product data.

Tracking classification as cited
Property	Value or range	Unit	Test conditions	Test method	Grade or construction	Source	Verification status
PLC 0	600 and greater	V	CTI test	IEC 60112 / ASTM D3638	Classification	S4	Confirm against the cited standard or source
PLC 1	400 to 599	V	CTI test	IEC 60112 / ASTM D3638	Classification	S4	Confirm against the cited standard or source
PLC 2	250 to 399	V	CTI test	IEC 60112 / ASTM D3638	Classification	S4	Confirm against the cited standard or source
PLC 3	175 to 249	V	CTI test	IEC 60112 / ASTM D3638	Classification	S4	Confirm against the cited standard or source
PLC 4	100 to 174	V	CTI test	IEC 60112 / ASTM D3638	Classification	S4	Confirm against the cited standard or source
PLC 5	less than 100	V	CTI test	IEC 60112 / ASTM D3638	Classification	S4	Confirm against the cited standard or source
Material group I	600 or above	V	CTI test	IEC 60112 as cited in UL 1950	Classification	S6	Typical illustrative range
Material group II	400 to below 600	V	CTI test	IEC 60112 as cited in UL 1950	Classification	S6	Typical illustrative range
Material group IIIa	175 to below 400	V	CTI test	IEC 60112 as cited in UL 1950	Classification	S6	Typical illustrative range
Material group IIIb	100 to below 175	V	CTI test	IEC 60112 as cited in UL 1950; eliminated after 2008	Classification	S6	Typical illustrative range

11. Why does moisture sensitivity matter?

Absorbed moisture lowers breakdown voltage, raises dielectric loss and can promote tracking. Papers, pressboard and some laminates are hygroscopic and are dried and impregnated before use; films absorb little. Ask for moisture content limits, drying conditions and storage requirements. This page gives no numbers.

12. What mechanical and flame characteristics matter?

Tensile strength, tear, elongation, stiffness and creasing behaviour for processing; compressive creep for supports; and flame classification such as a UL 94 rating where the equipment standard requires it. The one aramid paper data sheet read gives tensile, elongation and tear values by thickness, UL 94 ratings and a limiting oxygen index of 27–32% at room temperature (S5). Flame and smoke requirements belong to the equipment standard.

13. What does a full manufacturer data sheet look like for one product?

The DuPont data sheet for Nomex 410 aramid paper (form K-20612-2, 04/16) is a useful example of what to ask for. Its values are averages measured at 23 °C and 50% RH, not specification limits, and the sheet says the dielectric values are not recommended for design purposes. It gives eleven nominal thicknesses from 0.05 mm (2 mil) to 0.76 mm (30 mil) with basis weight, density, tensile strength and elongation (ASTM D828), tear (TAPPI 414 and ASTM D1004), AC rapid-rise dielectric strength (ASTM D149, 60 Hz, 10–20 s, 50 mm electrodes), full-wave impulse strength (ASTM D3426), dielectric constant and dissipation factor (ASTM D150), thermal conductivity (ASTM E1530), UL 94 ratings and a UL relative thermal index of 220 °C (electrical and mechanical), based on Arrhenius ageing plots (S5). It also gives humidity effects for the 0.25 mm grade, and states DuPont’s recommendation that continuous stress in transformers designed with this paper not exceed 1.6 kV/mm (40 V/mil) (S5). Internal inconsistencies are present (a 0.076 mm label for the 30 mil grade and a density of 1.13 g/cm³ for 0.61 mm that exceeds the 0.76 mm value), so even a primary sheet needs reading with care. Nothing here qualifies the material for any system.

Selected values from one aramid paper data sheet

From the DuPont Nomex 410 technical data sheet (form K-20612-2, 04/16). Averages at 23 °C and 50% RH, not specification limits, not for design. Grade-specific; do not apply to other products or thicknesses.

Selected values from one aramid paper data sheet
Property	Value or range	Unit	Test conditions	Test method	Grade or construction	Source	Verification status
Thickness, nominal grades	0.05 to 0.76 (2 to 30 mil)	mm	Eleven grades	ASTM D374	Nomex 410	S5	Manufacturer-specific value (one grade)
AC rapid-rise dielectric strength, 0.05 mm grade	18 (460 V/mil)	kV/mm	60 Hz, 10–20 s, 50 mm electrodes	ASTM D149	Nomex 410, 0.05 mm	S5	Manufacturer-specific value (one grade)
AC rapid-rise dielectric strength, 0.25 mm grade	33 (845 V/mil)	kV/mm	60 Hz, 10–20 s, 50 mm electrodes	ASTM D149	Nomex 410, 0.25 mm	S5	Manufacturer-specific value (one grade)
AC rapid-rise dielectric strength, 0.76 mm grade	27 (680 V/mil)	kV/mm	60 Hz, 10–20 s, 50 mm electrodes	ASTM D149	Nomex 410, 0.76 mm	S5	Manufacturer-specific value (one grade)
Dielectric strength, 0.25 mm, oven dry / 50% RH / 96% RH	33.5 / 33.2 / 30.7	kV/mm	Conditioned as stated	ASTM D149	Nomex 410, 0.25 mm	S5	Manufacturer-specific value (one grade)
Dielectric constant, 0.25 mm, oven dry / 50% RH / 96% RH	2.5 / 2.7 / 3.2	not applicable	60 Hz	ASTM D150	Nomex 410, 0.25 mm	S5	Manufacturer-specific value (one grade)
Volume resistivity, 0.25 mm, oven dry / 50% RH / 96% RH	6×10^16 / 2×10^16 / 2×10^14	ohm·cm	Conditioned as stated	ASTM D257	Nomex 410, 0.25 mm	S5	Manufacturer-specific value (one grade)
Tensile strength MD / XD, 0.25 mm	296 / 161	N/cm	23 °C, 50% RH	ASTM D828	Nomex 410, 0.25 mm	S5	Manufacturer-specific value (one grade)
UL relative thermal index (electrical and mechanical)	220	°C	Arrhenius ageing plots	UL 746B	Nomex 410, all thicknesses	S5	Manufacturer-specific value (one grade)
Recommended maximum continuous stress in transformers	1.6 (40 V/mil)	kV/mm	Designs using this paper	Manufacturer recommendation	Nomex 410	S5	Manufacturer-specific value (one grade)
Comparative tracking category (UL 746A)	3	performance level	All thicknesses	UL 746A	Nomex 410	S5	Manufacturer-specific value (one grade)

C. Manufacturing and processing

14. How are insulation materials made?

Films are extruded and often biaxially oriented; papers are formed from fibres or fibrids and calendered; laminates are layered and bonded with resin under heat and pressure; tapes are coated with adhesive; varnishes and resins are applied and cured. Processing steps determine thickness uniformity and voids, which matter for partial discharge. Details are proprietary.

15. What processing issues arise in use?

Cutting, slitting, punching and forming without cracking or fibre dust; winding and lapping tension; impregnation and cure schedules; and avoiding contamination. Keep processing environments clean and dry as the supplier states.

16. What failures appear and how are they diagnosed?

Failures, possible causes and checks
Observed problem	Possible cause	Check
Premature breakdown	Voids, contamination, moisture, thickness variation	Inspect for defects; moisture content; thickness map
Thermal ageing failure	Operating temperature above the thermal class of the system	Operating profile; system class evidence
Surface tracking	Contamination and humidity on the surface; low CTI	CTI data; creepage design; environment
Partial discharge	Voids or sharp edges at high stress	Partial-discharge test; impregnation quality
Delamination	Adhesive or resin incompatible with other materials	Compatibility and cure review
Brittle cracking after ageing	Thermal or chemical ageing	Ageing data for the system

Source basis: general engineering practice; no figures are drawn from the sources.

D. Applications and qualification

17. How should insulation be selected?

The equipment designer defines voltage, frequency, temperature profile, environment (humidity, oil, gas, contamination), mechanical loads, expected life and the applicable equipment standard. Candidates are then limited to materials with documented evidence for those conditions, and the insulation system is evaluated as a whole.

18. How should an insulation material be qualified?

Define the requirements from the equipment standard and design.
Obtain datasheet values with methods and conditions (dielectric strength, thickness, thermal class, CTI, moisture, mechanical).
Check the thermal class evidence (IEC 60216 ageing or UL listing) against the operating temperature.
Qualify the material as part of the insulation system with its tapes, varnish or resin.
Run application tests: dielectric withstand, partial discharge, ageing and environmental tests as the equipment standard requires.
Control change: re-evaluate when the material, supplier or process changes.

Source basis: S1 to S3; the sequence is general practice and not a replacement for the equipment standard.

19. Which documents should be requested?

Technical data sheet with test methods and conditions; thermal class or listing evidence (for example a UL file number where claimed); CTI and flammability data; moisture and storage statements; compatibility information; certificates of analysis; and change-notification terms.

20. What acceptance criteria are sensible?

Incoming checks usually include thickness, appearance, moisture or water content and, where agreed, a breakdown test on samples. Limits come from the design and specification; this page provides none.

21. How should insulation be stored and handled?

Dry, clean, wrapped and within the temperature range the supplier states; hygroscopic papers and laminates may need conditioning before use. General practice statements only.

E. Procurement, comparisons and decisions

22. Which commercial formats are common?

Rolls and slit tapes, sheets and sheeted stock, precut parts, laminates in plates and tubes, and impregnation resins in drums. Specify thickness, width, form and packaging.

23. What information is needed to request a quotation?

Equipment type and applicable standard; voltage and frequency.
Operating temperature and thermal class required; environment.
Material form, thickness, width and tolerances.
Required properties and test methods; documents needed.
Annual volume, packaging and destination.

Use the RFQ brief tool to assemble this in the browser.

24. What do purchasing teams usually ask?

What evidence supports the stated class; whether the material is used in qualified systems; lead time and minimum order; whether the supplier will notify of changes; and the manufacturer’s identity. Never accept a substitute grade without engineering approval.

25. How should cost and performance be compared?

Compare the cost of the insulation in the finished device with the cost of a failure and of re-qualification. A cheaper material that needs a derated system or re-testing may cost more overall.

26. What regulatory and sustainability questions arise?

Equipment standards, listings such as UL where relevant, flame and smoke rules, substance restrictions and end-of-life handling. This page makes no compliance declaration for any product.

27. What supplier qualification questions should be asked?

Who manufactures the material; what quality system applies; how lots are traced; what ageing and listing evidence exists; and how changes are notified. See the supplier qualification checklist. PAXOMER does not confirm any supplier’s approvals or capacity on this page.

Guide: Industrial material specification and supplier qualification checklist
Related page: Industrial desiccants and moisture control
Related page: PET spunbond roofing carriers
Tool: Solution Finder

Manufacturing Regions & International Supply

No country-level manufacturing evidence specific to Industrial Electrical Insulation was confirmed in the review.

If you are evaluating manufacturers abroad, list in your RFQ brief the destination market, the documents you require and the delivery terms.

Engineering and purchasing FAQs

Each answer is general technical information, not a specification or a quotation.

Can I use a material because it has a high thermal class?

Not on its own. A thermal class describes a material or system under defined ageing criteria. IEC 60085 states a material’s class cannot be applied to a system containing it without proof.

What does dielectric strength mean?

It is the voltage a specimen withstands before breakdown, usually in kV per unit thickness, under a specified test. ASTM D149 notes results rarely predict behaviour in service directly, and the figure depends on thickness, method and conditions.

What is the comparative tracking index?

A measure of surface tracking resistance using an ammonium chloride solution under voltage, with performance levels from PLC 0 (600 V and above) to PLC 5 (below 100 V). It is separate from dielectric strength.

Does a short-term temperature rating equal a thermal class?

No. A tape maker notes thermal classes give no information on short-term load temperature, which is usually much higher.

Why does moisture matter?

Absorbed water lowers breakdown voltage and promotes tracking and loss. Hygroscopic papers and laminates need drying and controlled storage.

Is aramid paper always the right choice for high temperature?

No. Choice depends on the system, voltage and environment. The one aramid paper data sheet read (S5) shows dielectric strength, thermal index and tracking category that apply only to that product and thickness, and says its values are averages, not design values.

Can a substitute material be used if the data sheet looks similar?

Not without engineering approval and re-evaluation of the insulation system. Similar single-point values do not show equivalence.

What information is needed for a quotation?

Equipment standard, voltage and frequency, operating temperature, environment, material form and thickness, required properties and documents, volume and destination.

Does PAXOMER supply specific electrical insulation materials?

This page does not confirm stock, representation, supply or qualification for any material, and it does not qualify any insulation for an electrical system. PAXOMER works in technical supply and manufacturer development; describe your application in an inquiry to discuss whether a suitable qualified manufacturer can be identified.

Technical References

References below were opened on the access date shown. A source supports only the statement it is cited for. Standards are cited by number and title from public catalogue entries; their full text was not read unless stated.

S1. IEC 60085:2004, Electrical insulation: thermal classification. iTeh Standards (IEC 60085:2004 listing), 2004. standards.iteh.ai/catalog/standards/iec/4bf9e47a-9ec6-4a56-a033-5f2011b1a319/iec (opens in a new tab) standard catalogue · accessed 2026-10-27
Catalogue mirror; status fields conflict (published and deleted); the standard was not read.
S2. Insulation classes / thermal classes. CMC Klebetechnik (insulation classes page). www.cmc.de/en/waermeklassen-klebeband (opens in a new tab) manufacturer literature · accessed 2026-10-27
Tape maker's explanatory page; table inconsistent for the top class; not a standard.
S3. ASTM D149-25, Dielectric breakdown voltage and dielectric strength of solid electrical insulating materials. ASTM International store (D149-25), 2025. store.astm.org/d0149-25.html (opens in a new tab) standard catalogue · accessed 2026-10-27
Store listing; scope read, standard not purchased.
S4. Comparative Tracking Index. Wikipedia (Comparative Tracking Index). en.wikipedia.org/wiki/Comparative_Tracking_Index (opens in a new tab) reference database · accessed 2026-10-27
Encyclopaedia article; secondary source; IEC 60112 and ASTM D3638 not read.
S5. Nomex 410 technical data sheet. DuPont (Nomex 410 technical data sheet, K-20612-2), 2016-04. blog.jbc-tech.com/media/1283/dpt16_21668_nomex_410_tech_data_sheet_me03_referenc (opens in a new tab) manufacturer datasheet · accessed 2026-10-27
Primary manufacturer sheet, hosted by a distributor (jbc-tech.com), form dated 04/16; the current DuPont/Arclin sheet may differ; two typographical inconsistencies noted.
S6. Comparative tracking index test. 3M (technical brief: comparative tracking index test). multimedia.3m.com/mws/media/1289893O/tech-brief-comparative-tracking-index-test. (opens in a new tab) manufacturer literature · accessed 2026-10-27
Manufacturer technical brief on its tapes citing UL 1950 and IEC 60112 (2003); undated; marketing disclaimers apply.
S7. IEC 60085:2007 Electrical insulation — Thermal evaluation and designation. IEC, 2007. webstore.iec.ch/en/publication/666 (opens in a new tab) standard catalogue · accessed 2026-10-29
Webstore entry opened 2026-10-29: current listed edition is 2007; full text not read.
S8. Nomex 410 and Nomex 400 Series. DuPont. www.pp.dupont.com/products/nomex-400-series.html (opens in a new tab) manufacturer literature · accessed 2026-10-29
Manufacturer product page opened 2026-10-29; links the current Type 410 data sheet, which was not compared with S5.

Evidence notes and limitations

What the information on this page does not establish. Confirm these points with the manufacturer, the current standard or the relevant authority before relying on them.

The 240 versus 250 °C top-class conflict is unresolved; the current IEC 60085 edition (2007 per the IEC webstore, S7) was not read. Specialist confirmation required.
The official DuPont Nomex 400-series page (S8) links the current Type 410 data sheet; the 2016 distributor-hosted sheet (S5) used for the table has not been compared with it.
IEC 60085, IEC 60216, IEC 60112, IEC 60243-1, ASTM D3638 and UL 1446 were not read; the IEC 60085 listing’s status is inconsistent and the current edition must be confirmed.
The tape maker’s thermal class table has an inconsistent top-class entry (240 vs 250 °C) and is a manufacturer explanation, not a standard.
The Nomex 410 sheet is a 2016 form hosted by a distributor; the manufacturer’s current sheet was not compared, and the values are averages, not specification limits. Its figures apply only to that product.
CTI performance level categories come from an encyclopaedia article; the 3M brief gives UL 1950 material groups; electrode spacing and the current IEC 60112 edition were not checked.
No data are given for polyester, polyimide, pressboard or laminate grades on this page; the film and tape short-term temperature statements come from the tape maker (S2).
Failure and selection tables are general practice.
This page does not qualify any material for any electrical system.
This page has not been independently technically reviewed or certified.

Facts checked against the cited sources

Thermal class definition, class list and the conflicting status were read in S1; temperatures and short-term caveats in S2.
ASTM D149-25 scope, methods and limits were read in S3.
Performance level categories were read in S4.
The Nomex 410 data sheet tables, test methods and recommendation were read in S5.
The CTI test conditions and material groups were read in S6.

Where this connects to the full guide

The primary technical guide behind this page is Switchgear & Electrical Assembly Insulation Materials. All its topics are indexed below.

Topics in the full guide

See all 22 topics in the guide

Glossary: Coefficient of thermal expansion · Dielectric breakdown · G10 · G11 · Tracking resistance · Arc resistance · Creepage distance · Electrical clearance · Busbar insulation · Partial discharge

Tools: Product Finder (Switchgear and electrical-assembly insulation materials; PCB prepreg and copper-clad laminates; Copper magnet wire and winding materials) · Solution Finder (Electrical insulation concern (specialist review required)) · Manufacturer Finder

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Describe your application, the specifications above and the qualification stage. The material and this page are carried into the form for you. PAXOMER replies by email; the form does not confirm stock, representation or qualification.

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