Magnet Wire Insulation Types: Enamel Systems Compared

Magnet wire insulation type is the chemistry of the enamel film: polyurethane, polyester, polyester-imide, polyamide-imide or polyimide. The chemistry decides whether the wire can be soldered, which chemicals it tolerates and the thermal class it can reach.

This guide covers the enamel coating types Jingda supplies on round magnet wire: how datasheets name them, how they compare and how to choose one.

What “insulation type” means on a magnet wire datasheet

On a datasheet, insulation type names the enamel chemistry, and thermal class names the temperature rating that chemistry earned in thermal endurance testing. The two are linked but not interchangeable.

The thermal class belongs to a specific chemistry and construction, tested on a specific conductor. The same basecoat and topcoat chemistry, for example, is rated Class 200 on copper (NEMA MW 35-C) and Class 220 on aluminum (NEMA MW 35-A) in the Jingda range. A thicker film does not raise the class.

Datasheets usually identify the insulation type in three or four ways at once:

• IEC 60317 part number. IEC 60317 is the international specification series for particular types of winding wire. Each part covers one insulation system and one thermal class, so the part number alone tells you both.
• NEMA MW type. ANSI/NEMA MW 1000 is the North American magnet wire standard. Its Annex C cross-references MW type numbers to the corresponding IEC 60317 parts.
• JIS type code. JIS C 3202 uses short codes that name the chemistry directly: PEW (polyester), EIW (polyester-imide), AIW (polyamide-imide), PIW (polyimide) and UEW (polyurethane).
• Type designation. Chinese GB codes such as QZY-*/180 or QY-*/240 combine a chemistry code with the thermal class.

When two documents disagree, go back to the standard part number. This guide deals with chemistry. Thermal classes and their test basis are covered in our guide to magnet wire insulation class.

What the enamel film has to do

The enamel film does four jobs at once.

• Separate adjacent turns. Without the film, touching turns in a coil would short, and current would bypass the winding instead of following the conductor.
• Withstand voltage. The film’s dielectric properties and thickness set how much voltage the wire can take between turns before breakdown, including transient spikes.
• Survive winding. High-speed winding drags the wire over tooling and neighboring turns, so the film has to resist abrasion and stretching without cracking.
• Resist the environment. Moisture, varnishes, oils, refrigerants and cleaning agents all reach the film. How well a chemistry tolerates them is often what separates two insulation types that share a thermal class.

No single chemistry is best at all four. That is why several insulation types exist, and why overcoated constructions combine two of them.

The insulation systems Jingda supplies

Jingda supplies polyurethane, polyester, polyester-imide, dual-coat polyester-imide with a polyamide-imide overcoat, polyamide-imide and aromatic polyimide enamels, plus self-bonding and corona-resistant grades. Each system below follows the same order: chemistry, thermal class, solderability, typical use and standard designations.

Polyurethane (UEW): solderable, Class 155 and 180

Polyurethane enamel decomposes at soldering temperature, so coil terminations can be tinned without mechanically stripping the film. It is the usual choice when a coil has many terminations or the wire is too fine to strip reliably.

• Thermal classes: 155 and 180.
• Solderability: direct solderable. The exact solder-bath temperature and immersion time are stated in the product specification and depend on conductor size and film build.
• Typical applications: small motor coils, relays and solenoids, sensor coils and other magnetic coils.
• Standard designations: IEC 60317-20 (Class 155) and IEC 60317-51 (Class 180); NEMA MW 79-C (155) and MW 82-C (180); JIS UEW; type designations QA-*/155 and QA-*/180.
• Aluminum conductor: solderable grades are also offered on aluminum (NEMA MW 79-A and MW 82-A); see the product page for scope.

The trade-off is the thermal ceiling. Where a winding has to be rated above Class 180, a non-solderable system is needed. See our solderable magnet wire for available grades.

Polyester and polyester-imide (PEW / EIW): Class 155 and 180

Polyester (PEW) and polyester-imide (EIW) are single-coat enamels for general home-appliance motor and transformer windings. Modifying the polyester resin with imide groups raises the thermal class from 155 to 180 (Class H).

• Thermal classes: 155 for polyester, 180 for polyester-imide.
• Solderability: not direct solderable.
• Typical applications: general home-appliance motors and transformer coils; polyester is also used for magnetic coils.
• Standard designations: polyester to IEC 60317-3, NEMA MW 5-C, JIS PEW, type designation QZ-*/155; polyester-imide to IEC 60317-8, NEMA MW 30-C, JIS EIW, type designation QZY-*/180.

Polyester-imide is also the basecoat of the dual-coat 200-class system below. When a design needs more abrasion or chemical margin than a single coat gives, the overcoated version is the next step. Round copper grades in both systems are listed on our copper magnet wire page.

Polyester-imide with polyamide-imide overcoat (EI/AIW): Class 200 copper, Class 220 aluminum

This dual-coat system uses a polyester or polyester-imide basecoat for thermal and chemical resistance and a polyamide-imide topcoat for abrasion and winding stress. In the Jingda range it is one of the most widely used high-temperature constructions.

• Thermal classes: 200 on copper; 220 on aluminum.
• Solderability: not direct solderable. Terminations are stripped mechanically or chemically.
• Chemical resistance: refrigerant resistance for hermetic compressor systems (copper) and refrigeration compressor windings (aluminum).
• Typical applications (copper, Class 200): hermetic compressors, power tool motors, automotive motors and water pump motors.
• Typical applications (aluminum, Class 220): refrigeration compressors, industrial motors, appliance motors and transformers.
• Standard designations, copper: IEC 60317-13; NEMA MW 35-C and MW 73-C; JIS EI/AIW; type designation Q(ZY/XY)-*/200.
• Standard designations, aluminum: NEMA MW 35-A and MW 73-A; JIS EI/AIW; type designation Q(ZY/XY)-*/220. Aluminum grades follow the general requirements of IEC 60317-0-3, with test methods per IEC 60851.

The lubricated polyamide-imide surface is what makes this construction suit automatic winders. Grade 1, 2 and 3 builds are available on the copper version. Specifications are on the 200 class enameled copper wire page and, for aluminum conductor, the aluminum magnet wire page.

Polyamide-imide (AIW): Class 220 copper

A single polyamide-imide enamel reaches Class 220 on copper. It is used where a winding needs more thermal margin than the dual-coat 200-class system but does not call for polyimide.

• Thermal class: 220.
• Standard designations: IEC 60317-57; NEMA MW 81-C; JIS AIW; type designation QXY-*/220.
• Properties: good heat resistance and good mechanical strength of the film.
• Typical applications: general industrial motors, open-type home-appliance motors and transformer coils.
• Solderability: not direct solderable. Chemical resistance: see datasheet.

Aromatic polyimide (PIW): Class 240

Aromatic polyimide is the highest-rated enamel in the Jingda range, at Class 240. It resists common solvents, but it is not designed for direct soldering through the film.

• Thermal class: 240.
• Solderability: not direct solderable.
• Chemical resistance: excellent resistance to common solvents.
• Typical applications: aerospace motors and actuators, smoke-extraction fans, high-temperature automotive motors and high-temperature sensors.
• Standard designations: IEC 60317-46; NEMA MW 16-C; JIS PIW; type designation QY-*/240.

See our polyimide magnet wire for sizes and builds.

Self-bonding overcoat

A self-bonding wire carries an extra bonding layer over its base insulation. After winding, heat or solvent activates the layer and fuses adjacent turns, so the coil holds its shape without a bobbin, tape or varnish impregnation.

• How it is used: the coil is wound, then bonded, typically by passing current through the winding, oven curing or solvent activation. The bonding method has to suit the bonding layer’s chemistry.
• Typical applications: automotive motors, power tools and motor coils. More generally, self-bonding wire suits any winding that must stay self-supporting after forming, such as air-core coils.
• Jingda grade: polyester-imide / polyamide-imide base (SBEIAIW), Class 200 (type designation Q(ZY/XY)N-*B/200), NEMA MW 102-C.

Self-bonding round copper grades are listed on our copper magnet wire page.

Corona-resistant and inverter-duty grades

Corona-resistant enamels are made for windings driven by inverters, where fast voltage rise times and overshoot at the motor terminals can cause partial discharge between turns. The enamel contains inorganic fillers that slow erosion when partial discharge occurs.

• When they are needed: when the peak voltage between turns, including inverter overshoot, can exceed the winding’s partial discharge inception voltage. Common cases are variable-frequency drives, electric vehicle traction motors and fast-switching power electronics.
• When they are not: mains-fed motors and transformers without fast switching transients rarely need them. A standard grade with an adequate build is usually sufficient.
• Jingda supply: two corona-resistant copper grades: polyamide-imide, Class 220 (type designation BP-*/220), and polyester-imide with a polyamide-imide overcoat, Class 200 (Q(ZY/XY)BP-*/200). Listed uses include new energy vehicle drive motors, wind power generators and industrial variable-frequency motors.

Partial discharge behavior depends on the whole insulation system, including slot liners, varnish and winding layout, so wire selection is one input to that evaluation.

Magnet wire insulation types compared

The table compares each insulation system by thermal class, direct solderability, solvent and refrigerant resistance, corona resistance, typical applications, type designation and standards. Values come from Jingda’s product pages and product documents.

Read the table as a starting point. Grades within one insulation type differ in build, lubricant and test values; design against the product datasheet.

How to choose a magnet wire insulation type

Start from the application: its hot-spot temperature, how the coil is terminated and what chemicals the winding will meet. Then choose the insulation type that meets all three.

Wire thermal class is one input to system evaluation; the insulation system as a whole is evaluated separately.

Industrial motors. In the Jingda range, the dual-coat EI/AIW system and single-coat polyamide-imide are the main candidates. For inverter-fed industrial motors, the corona-resistant grades apply. For OEM motor programs, see motor winding wire.

Compressors and home appliances. In hermetic compressors the film sits in refrigerant and oil for the life of the unit, so chemical resistance weighs as much as thermal class. See compressor winding wire.

Electronics. Fine coils with many terminations favor polyurethane, because each termination can be soldered without stripping. See fine magnet wire.

Electric vehicles. Traction motors combine high thermal class with inverter drive, so partial discharge is part of the insulation decision from the start. See electric motor wire.

Insulation build (Grade 1 / 2 / 3) vs insulation type

Build is how thick the enamel film is; insulation type is what the film is made of. Grade 1, 2 and 3 (Single, Heavy and Triple builds) increase film thickness but do not change the thermal class.

The two are often confused because both appear in the same line of a datasheet: for example, a Class 200 wire in Grade 2 build. The class comes from the chemistry. For each nominal conductor diameter, the standard sets the minimum increase in diameter due to the enamel and the maximum overall diameter for each grade.

A heavier build has costs as well as benefits. It raises breakdown voltage and partial discharge inception voltage, and it gives more tolerance to winding damage. It also increases overall diameter, which lowers how much conductor fits in a given slot or window. Jingda supplies Grade 1 to Grade 3 builds, with diameters specified in metric and AWG sizes.

Uniformity matters as much as thickness

A film is only as strong as its thinnest point. Variation in coating thickness, pinholes and poor adhesion to the conductor all create sites where breakdown starts early under electrical or thermal stress.

Multi-pass coating, in which the film is built up in several thin layers with a cure between passes, is the industry’s standard way to keep the film uniform. Inline high-voltage continuity testing then detects faults before the wire is spooled. Adhesion matters for the same reason: film that lifts during bending or thermal cycling leaves voids where discharge can start.

Frequently asked questions

Request a quote or a datasheet

Send us the insulation type, thermal class, conductor, diameter and build, and we will reply with a quotation within 1 business day. Minimum order quantity is 600 kg per specification, and FOB is the default term.

Datasheets are available through View Datasheet on the individual product pages. The full range is on our magnet wire page.

Tongling Jingda Special Magnet Wire Co., Ltd. has manufactured enameled wire since 1990 to IEC 60317, NEMA MW 1000 and JIS C 3202. UL Recognized constructions are available, and the UL status of a specific grade is confirmed on request. Production runs under an ISO 9001 quality system.

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