Enamelled winding wire

Class 130 / 155 Polyester Enamelled Round Aluminium Wire

Polyester enamelled aluminium wire is annealed electrical aluminium coated with a baked polyester film rated to thermal class 130 (class B) or 155 (class F). It is the economical general-purpose winding wire for small and medium motors, transformers and household appliances. Metline supplies it in grades 1 to 3, from fine to heavy sizes, on spools matched to your winding equipment, to customers worldwide.

By Metline Technical Team · Updated 17 October 2026

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Polyester enamelled aluminium winding wire on spools for motor and transformer production — Photo: Kreuzschnabel, Wikimedia Commons, CC BY-SA 3.0

Thermal class: 130 (B) or 155 (F)
Insulation: Modified polyester
Diameter: 0.25 – 5.0 mm
Film grades: Grade 1, 2, 3

Overview

What polyester enamelled aluminium wire is

Polyester (often THEIC-modified polyester for class 155) was the first high-performance synthetic enamel and is still among the most widely used. It combines good dielectric strength, solvent resistance and adhesion with low cost.

The conductor is high-conductivity aluminium, drawn to size and annealed in-line to the soft O temper so it winds smoothly and holds shape. Enamel is applied by dies or felts in many thin coats, each baked, which builds a uniform, concentric film free of pinholes. A final surface lubricant reduces friction for high-speed automatic winding.

Class 130 polyester is used where winding temperatures are moderate; the modified class 155 version extends the hot-spot limit by 25 °C for motors and transformers that run harder. Where more margin is needed, the same conductor can be supplied with class 180 polyesterimide or class 200 dual-coat insulation.

Property	Class 130 polyester	Class 155 modified polyester
Temperature index	≥ 130	≥ 155
IEC insulation class letter	B	F
Typical heat-shock test temperature	155 °C	175 °C
Main uses	Small motors, fans, ballasts, appliance coils	General industrial motors, transformers, power tools

Conductor choice

Why use an aluminium conductor?

Annealed aluminium winding wire conducts about 61 % as well as annealed copper by volume, with a maximum resistivity close to 0.02826 Ω·mm²/m against 0.01724 for copper. Because it is less than a third as dense, an aluminium winding with the same resistance weighs only about half as much as the copper one.

For equal resistance	Copper winding	Aluminium winding
Conductor cross-section	1.00	about 1.64
Conductor diameter	1.00	about 1.28
Conductor mass	1.00	about 0.50
Material cost	Higher, and volatile	Typically much lower per amp

The trade-offs are larger coil size and more care at terminations, because aluminium forms a hard oxide skin and creeps under clamping pressure. Distribution transformers, appliance motors and ballasts are classic aluminium applications; compact, high-power-density motors usually stay with copper.

Dimensions

Diameters, film thickness and overall diameter

Nominal diameters and film limits follow the IEC 60317-0-3 R20 series. The table shows a selection of sizes for grades 1 and 2; grade 3 is available for higher voltage stress.

Nominal diameter (mm)	Tolerance (mm)	Min. film increase, grade 1 (mm)	Min. film increase, grade 2 (mm)	Max. overall diameter, grade 1 (mm)	Max. overall diameter, grade 2 (mm)
0.250	±0.004	0.017	0.032	0.281	0.297
0.400	±0.005	0.021	0.040	0.439	0.459
0.500	±0.005	0.024	0.045	0.544	0.566
0.630	±0.006	0.027	0.050	0.679	0.704
0.800	±0.008	0.030	0.056	0.855	0.884
1.000	±0.010	0.034	0.063	1.062	1.094
1.250	±0.013	0.035	0.067	1.316	1.349
1.600	±0.016	0.038	0.071	1.670	1.706
2.000	±0.020	0.040	0.075	2.074	2.112
2.500	±0.025	0.042	0.079	2.578	2.618
3.150	±0.032	0.045	0.084	3.233	3.276
4.000	±0.040	0.047	0.089	4.088	4.133
5.000	±0.050	0.050	0.094	5.093	5.141

North American orders can be supplied to NEMA MW 1000 AWG sizes in single or heavy build; aluminium constructions carry an "-A" suffix in the NEMA designation.

Test requirements

Mechanical and electrical requirements

Nominal diameter (mm)	Minimum elongation	Minimum tensile strength
up to 0.400	10 %	90 N/mm²
0.400 – 1.000	12 %	90 N/mm²
1.000 – 2.000	15 %	80 N/mm²
2.000 – 5.000	15 %	70 N/mm²

Nominal diameter (mm)	Breakdown voltage, grade 1 (V rms, min.)	Breakdown voltage, grade 2 (V rms, min.)
0.250	2,100	3,900
0.315	2,200	4,100
0.400	2,300	4,400
0.500	2,400	4,600
0.630	2,600	4,800
0.800	2,600	4,900
1.000 – 2.500	2,700	5,000

Other routine tests include continuity (pinholes), adherence and flexibility (mandrel winding after elongation), springback, heat shock, cut-through, solvent resistance and minimum scratch force: at least 1.95 N mean for grade 1 and 3.15 N for grade 2 at 0.40 mm, rising with diameter.

Options

Self-bonding and special versions

Self-bonding (bondcoat)

A thermoplastic outer layer fuses turns together when heated by oven or current, or activated by solvent. It removes the need for varnish in voice coils, deflection coils and some small transformers.

Lubricated for automatic winding

Low-friction surface for high-speed needle and flyer winders and for slot insertion, reducing film damage and broken wires.

Thicker film (grade 3)

For higher inter-turn voltages or extra mechanical protection in rugged coils.

Upgrade path

Where the motor runs hotter than class 155, move to class 180 PEI or class 200 dual-coat wire on the same aluminium conductor.

Quality

How the wire is made and checked

DrawElectrical-grade aluminium rod is drawn through diamond or carbide dies to the bare diameter.
AnnealIn-line annealing restores full softness and elongation, then the wire is cooled and cleaned.
Enamel and bakePolyester enamel is applied in repeated thin coats and cured in a vertical or horizontal oven to the specified grade.
Lubricate and testA surface lubricant is applied; on-line instruments monitor diameter and pinholes continuously.
Spool and certifyThe wire is wound onto spools, and each lot is tested and documented before dispatch.

Applications

Typical applications

Windings of small and medium general-purpose motors
Distribution, control and instrument transformers and reactors
Household appliance motors: fans, washing machines, refrigerators (outside the hermetic system), microwave ovens
Ballasts, chokes, relay and solenoid coils
Power tools and small generators where cost and weight matter

For hermetic refrigeration compressors, specify wire qualified for refrigerant compatibility, such as a class 200 dual-coat construction.

Sources

References and standards

IEC 60317-0-3 – General requirements: enamelled round aluminium wire
IEC 60851 series – Winding wires: test methods
NEMA MW 1000 – Magnet wire
IEC 60085 – Electrical insulation: thermal evaluation and designation

FAQ

Polyester enamelled aluminium (aluminum) wire: FAQs

What is the difference between class 130 and class 155 polyester wire?

Class 155 uses a modified (usually THEIC) polyester with a temperature index of at least 155, compared with 130 for standard polyester. It tolerates higher winding temperatures and has better heat-shock performance.

How is enamelled aluminium wire made?

Aluminium rod is drawn to size, annealed, coated with enamel in many thin passes that are each baked, lubricated, tested on line and wound onto spools.

Can I replace copper wire with aluminium wire of the same size?

Not directly. For the same resistance, aluminium needs about 1.64 times the cross-section, or about 1.28 times the diameter. Check slot fill, temperature rise and terminations before converting.

Which film grade should I choose?

Grade 1 for compact, low-voltage coils; grade 2 for most motors and transformers; grade 3 where inter-turn voltage is high or extra mechanical protection is needed.

What spools are available?

Plastic and wooden spools of standard PT-series sizes, conical spools and payoff drums, with net weights up to about 150 kg depending on diameter.

Is self-bonding polyester wire available?

Yes. Bondcoat versions activated by heat, current or solvent can be supplied for coils that must hold shape without varnish.