Distribution transformers
Low- and high-voltage layer windings in oil-immersed and dry-type units, often alongside aluminium foil windings.
Guide · Rectangular winding wire
Enamelled Aluminium Flat Wire
Enamelled aluminium flat wire is a rectangular aluminium conductor with rounded corners and a thin baked-on polymer insulation, used to wind transformers, reactors, motors and inductors. The flat shape packs more conductor into a winding window than round wire, and aluminium cuts winding weight and material cost compared with copper. This guide covers conductor sizes, insulation classes, the governing IEC and NEMA standards and how to specify the wire.
- Conductor
- EC aluminium, annealed
- Thickness × width
- About 1.0 – 5.6 × 2 – 16 mm
- Thermal class
- 120 – 220
- Standard
- IEC 60317-0-9 · NEMA MW 1000
What enamelled aluminium flat wire is
Flat (rectangular) magnet wire is drawn or rolled to a precise thickness and width, given radiused corners so the enamel covers the edges evenly, then passed repeatedly through an enamelling line that applies and cures thin layers of insulating resin. The result is a conductor that can be wound tightly in layers with very little wasted space.
Compared with round wire, a rectangular conductor fills the winding space much more completely, because round wires leave gaps between turns. In a transformer or reactor this means either a smaller core window for the same rating or more conductor area and lower losses in the same window. The flat faces also give larger contact between layers, which improves heat transfer to the cooling ducts.
Using aluminium instead of copper changes the design rules. Annealed EC aluminium has about 61 % of the conductivity of copper, so the cross-section must be about 1.6 times larger for the same resistance, but the conductor weighs about half as much and costs considerably less. Aluminium flat wire is well established in distribution and dry-type transformers and reactors, and is used in motors and generators where weight and cost outweigh the need for the most compact winding.
Conductor material and dimensions
The conductor is high-purity electrical aluminium (typically 1350, 1060 or 1070) in the fully annealed condition, which gives maximum conductivity and the ductility needed for edgewise and flatwise bending. Conductor dimensions are specified as thickness (a) × width (b), with a corner radius chosen to suit the thickness.
Typical conductor range
- Thickness (a)
- About 1.0 – 5.6 mm
- Width (b)
- About 2.0 – 16 mm; larger sections by arrangement
- Width-to-thickness ratio
- Usually between about 1.4 and 8, to keep the wire stable during winding
- Corner radius
- Rounded edges sized to the thickness, commonly 0.5 mm up to about 1 mm, to protect the enamel at the edges
- Resistivity
- About 0.0283 Ω·mm²/m at 20 °C (approximately 61 % IACS)
- Elongation
- High, typically 30 % or more in the annealed condition
The table shows calculated conductor area, weight and DC resistance for representative sizes. The area allows for the corner radii, which remove a small amount of metal from each corner.
| a × b (mm) | Corner radius (mm) | Area (mm²) | Conductor weight (kg/km) | DC resistance at 20 °C (Ω/km) |
|---|---|---|---|---|
| 1.0 × 4.0 | 0.50 | 3.79 | 10.2 | 7.47 |
| 1.5 × 6.0 | 0.50 | 8.79 | 23.7 | 3.22 |
| 2.0 × 8.0 | 0.65 | 15.64 | 42.2 | 1.81 |
| 2.5 × 10.0 | 0.80 | 24.45 | 66.0 | 1.16 |
| 3.0 × 12.0 | 0.80 | 35.45 | 95.7 | 0.80 |
| 4.0 × 12.5 | 0.80 | 49.45 | 133.5 | 0.57 |
| 5.0 × 16.0 | 0.80 | 79.45 | 214.5 | 0.36 |
Area = a × b − (4 − π) r². Weight excludes enamel; the insulation adds roughly 1 – 3 % depending on build. Resistance uses 0.02826 Ω·mm²/m.
Insulation types and thermal classes
The enamel system decides the thermal class, chemical resistance and how the wire behaves in varnish, oil or refrigerant. Thermal class is the temperature in °C at which the insulation gives a defined service life in thermal-endurance testing.
| Thermal class (IEC 60085 letter) | Typical enamel | Typical use |
|---|---|---|
| 120 (E) | Polyvinyl acetal (polyvinyl formal) | Oil-filled transformers, where acetal resists transformer oil well |
| 130 (B) | Polyester | General motors and small transformers |
| 155 (F) | Modified polyester | Industrial motors, dry-type transformers |
| 180 (H) | Polyesterimide | Higher-temperature motors and dry-type transformers |
| 200 | Polyesterimide with polyamide-imide overcoat | Inverter-fed motors, hermetic and high-overload windings |
| 220 | Polyamide-imide | Severe thermal and mechanical duty |
Grade refers to insulation build. Grade 1 is a thinner film for maximum conductor area; Grade 2 is a thicker film with higher breakdown voltage and better resistance to mechanical damage during winding. Rectangular wires are normally offered in Grade 1 and Grade 2, with thicker builds possible for special high-voltage windings. Choose the grade from your turn-to-turn voltage, the winding method and whether additional paper or film insulation is used between layers.
- For oil-immersed transformers, confirm compatibility of the enamel with transformer oil and with the impregnation varnish.
- For inverter-fed motors, consider dual-coat 200-class systems for resistance to voltage spikes and partial discharge.
- For hermetic compressors, the enamel must be qualified for the refrigerant and oil in use.
Standards and routine tests
| Standard | What it covers |
|---|---|
| IEC 60317-0-9 | General requirements for enamelled rectangular aluminium winding wire |
| IEC 60317 specification sheets | Particular enamel types and thermal classes, e.g. polyvinyl acetal class 120 rectangular aluminium |
| IEC 60851 series | Test methods for winding wires: dimensions, elongation, springback, flexibility, breakdown voltage, heat shock, solvent resistance |
| IEC 60172 | Determining the temperature index of enamelled winding wires |
| NEMA MW 1000 | North American magnet wire standard, including aluminium rectangular wires |
| IEC 60085 | Thermal classification of electrical insulation |
Routine production tests normally include conductor dimensions and corner radius, insulation thickness, elongation, flexibility and adherence (bending the wire edgewise and flatwise around mandrels and checking for cracks), breakdown voltage at room and elevated temperature, continuity of the film, and DC resistance. Ask for the test report with each lot.
Where aluminium flat wire is used
Reactors and inductors
Air-core and iron-core reactors, filter chokes and line reactors where weight and cost dominate.
Motors and generators
Stator coils in industrial motors and generators where the frame size allows the larger aluminium section.
Traction and rail equipment
Transformers and inductors where reducing mass on the vehicle is valuable.
Welding and power supplies
Transformer and inductor windings in welding sets, UPS and inverter equipment.
Electric vehicles
Most traction-motor hairpins are copper today; aluminium flat wire is evaluated for on-board inductors, transformers and cost-focused motors.
Aluminium vs copper flat wire
| Factor | Aluminium flat wire | Copper flat wire |
|---|---|---|
| Conductivity | About 61 % IACS | About 100 % IACS |
| Cross-section for equal resistance | About 1.6× copper | Reference |
| Weight for equal resistance | About 50 % | Reference |
| Winding size | Larger window or coil | Most compact |
| Material cost | Lower and steadier | Higher and more volatile |
| Terminations | Needs welding, crimping or cold-pressure methods suited to aluminium | Brazing and soldering are straightforward |
Aluminium makes most sense where the winding can grow slightly and weight or cost is a priority; copper keeps the edge where space is fixed. Metline supplies the aluminium flat wire; for terminations to copper leads, bimetallic connectors or welding methods designed for aluminium avoid galvanic problems.
How to specify and order
- ConductorThickness × width and corner radius, with tolerances, and the conductor grade if specified.
- InsulationEnamel type, thermal class and grade (insulation build), plus any compatibility needs such as oil or refrigerant.
- StandardIEC 60317-0-9 with the relevant specification sheet, NEMA MW 1000 or your own specification.
- PackagingSpool type (for example PT-series) and maximum weight per spool to suit your winding machines.
- DocumentsTest report per lot covering dimensions, breakdown voltage, elongation and resistance; terms EXW, FOB, CIF or DAP.
References and standards
- IEC 60317-0-9 – Winding wires: general requirements, enamelled rectangular aluminium wire
- IEC 60851 – Winding wires: test methods
- IEC 60172 – Test procedure for the determination of the temperature index of enamelled winding wires
- NEMA MW 1000 – Magnet Wire
- IEC 60085 – Electrical insulation: thermal evaluation and designation
Enamelled aluminium (aluminum) flat wire: frequently asked questions
What is the advantage of flat wire over round wire?
Rectangular wire leaves far fewer gaps between turns, so more conductor fits in the same winding window. That lowers losses or allows a smaller core, and the flat faces transfer heat better between layers.
How much larger must aluminium flat wire be than copper?
About 1.6 times the cross-section for the same DC resistance, because annealed aluminium has roughly 61 % of copper's conductivity. The aluminium winding still weighs about half as much.
Which thermal class should I choose?
Match it to the hot-spot temperature of the winding: 120 for many oil-immersed transformers, 155 or 180 for dry-type transformers and industrial motors, and 200 or 220 for inverter-fed or high-overload duty.
What is the difference between Grade 1 and Grade 2 enamel?
Grade 2 has a thicker insulation build than Grade 1, giving higher breakdown voltage and better resistance to winding damage, at the cost of slightly less conductor in the window.
Which standard covers enamelled rectangular aluminium wire?
IEC 60317-0-9 sets the general requirements, with individual IEC 60317 sheets for each enamel type. In North America, NEMA MW 1000 is used.
Can you supply custom sizes and spools?
Yes. Conductor size, corner radius, enamel system, grade and spool type can be specified, with test reports per lot and export packing for delivery worldwide.
Need aluminium flat wire for a winding project?
Send conductor size, enamel class, grade, spool type and quantity. We will reply with a matched specification and delivered price.
