Aluminium winding wire is a fully annealed, high-purity aluminium conductor (normally 1350 or 1370), drawn to round or rectangular section and insulated with enamel, paper or fibre so it can be wound into coils. It carries about 61 % of the conductivity of copper at roughly one third of the density, so a winding of equal resistance is about half the weight. This guide explains how to choose it against copper and copper-clad aluminium, which insulation class to specify and how to size and terminate it.
Every motor, transformer, reactor, ballast, solenoid and relay contains a coil, and the coil is wound from winding wire (also called magnet wire). For most of the twentieth century that wire was copper. Aluminium has taken a growing share since the 1960s, first in distribution transformers and later in fan motors, compressors, air-conditioner motors and induction cookers, because it delivers the same electrical job for less weight and, at most points in the metal price cycle, for less money.
The conductor is electrical-conductor (EC) grade aluminium of at least 99.5 % purity, registered as alloy 1350 (EN AW-1350, UNS A91350), or the slightly higher-conductivity 1370. Wire rod is drawn down through a series of dies and then fully annealed so the conductor is soft enough to wind tightly without cracking the insulation. Insulation is applied in-line: several thin coats of enamel for round and small flat wire, or wrapped paper, polyester film, aramid or glass fibre for larger rectangular conductors used in oil-filled and dry-type transformers.
Three things decide whether aluminium is the right conductor for a coil: the space available for the winding, the importance of weight and material cost, and how the coil ends will be joined. The rest of this guide works through each of these, with the numbers you need for a first-pass design.
The table compares the three conductors used for winding wire. Values are typical for annealed conductor at 20 °C: copper is the International Annealed Copper Standard (100 % IACS), aluminium is EC-grade 1350, and CCA is aluminium wire with a metallurgically bonded copper skin of 10 % or 15 % by volume, as covered by ASTM B566.
| Property | Aluminium (1350-O) | Copper (annealed) | CCA (10 – 15 % Cu) |
|---|---|---|---|
| Conductivity | ≈ 61 – 62 % IACS | 100 % IACS | ≈ 62 – 65 % IACS |
| Resistivity at 20 °C | ≈ 0.028 Ω·mm²/m | 0.01724 Ω·mm²/m | Close to aluminium |
| Density | 2.70 g/cm³ | 8.89 g/cm³ | ≈ 3.3 – 3.6 g/cm³ |
| Temperature coefficient of resistance | ≈ 0.0040 /°C | ≈ 0.0039 /°C | ≈ 0.0040 /°C |
| Thermal conductivity | ≈ 230 W/m·K | ≈ 390 W/m·K | Between the two |
| Tensile strength (annealed) | Low; soft conductor | About 3 × aluminium | Slightly above aluminium |
| Termination | Needs oxide-breaking method | Solders and crimps easily | Solders like copper on the surface |
| Relative weight for equal resistance | ≈ 0.5 | 1.0 | ≈ 0.55 – 0.6 |
The practical consequence is a simple trade. To match the resistance of a copper winding, an aluminium conductor needs about 63 % more cross-sectional area, which means a diameter about 28 % larger. Even with that extra area, the aluminium winding weighs only about 49 % as much as the copper one, because aluminium is so much lighter. Designers therefore accept a slightly larger winding window in return for a much lighter, and usually cheaper, coil.
CCA sits between the two. Its copper skin gives a solderable surface and slightly better high-frequency behaviour, because at high frequency current crowds into the outer layer of the conductor. It is widely used for voice coils, small appliance motors and some telecommunication coils. For low-frequency power windings, where current flows through the whole section, CCA behaves almost like aluminium electrically and costs more, so solid aluminium is usually the better value.
Ratios above are calculated from conductivity and density, taking aluminium at 61.5 % IACS. Check the exact conductivity on the wire certificate for your design.
The standard form for motors, small transformers, ballasts and coils. Typical nominal diameters run from about 0.2 mm to 5 mm. Grade 1, 2 or 3 refers to enamel build: thicker builds give higher breakdown voltage at the cost of a little winding space.
Fills the winding window far better than round wire because there are no gaps between turns. Used in traction and EV motors, welding transformers, reactors and compact dry-type transformers. Edge radius and aspect ratio must suit the winding machine.
Rectangular or round aluminium wrapped in layers of kraft or crêpe paper, then impregnated with transformer oil in service. The traditional insulation for oil-filled distribution and power transformers. See our paper-covered magnet wire guide.
Glass yarn, polyester film or aramid paper wraps for dry-type transformers, traction motors and high-temperature coils, often over an enamel base coat and bonded with varnish.
Uninsulated round or flat wire, plus aluminium strip and foil for foil-wound low-voltage transformer windings. Foil windings are covered in our transformer foil and strip guide.
Self-bonding wire has a thermoplastic top coat that fuses turns together when heated, removing the need for varnish. Litz wire bundles many fine insulated strands to reduce AC losses at high frequency; aluminium Litz is used in some induction-heating and wireless-charging coils.
The thermal class of a winding wire is the temperature, in °C, at which the insulation is expected to give a satisfactory life under continuous operation. Classes follow IEC 60085 and the temperature index tests in IEC 60172. Choose a class at least one step above the hot-spot temperature calculated for the coil, so that overloads and ambient extremes do not shorten its life.
| Thermal class | Letter | Typical enamel chemistry | Typical use |
|---|---|---|---|
| 130 °C | B | Polyester, polyurethane | Small motors, relays, general coils |
| 155 °C | F | Modified polyester, polyurethane (solderable) | Appliance motors, ballasts, small transformers |
| 180 °C | H | Polyesterimide | Industrial motors, compressors, dry-type transformers |
| 200 °C | N | Polyesterimide base with polyamide-imide overcoat | Hermetic compressors, high-load motors, traction |
| 220 °C | R | Polyamide-imide or polyimide | High-temperature motors, aerospace and specialist coils |
A dual-coat construction (a polyesterimide base with a polyamide-imide top coat) is the workhorse of modern motor winding because the hard top coat resists the abrasion of high-speed automatic winding and the base coat gives good adhesion and thermal life. For hermetic refrigeration compressors, the enamel must also resist refrigerants and compressor oil, which is a separate qualification test.
Polyurethane enamels are "solderable": the coating burns off in a hot solder bath, which is convenient on copper. On aluminium the bath removes the enamel but not the tough natural oxide, so solderable enamel does not by itself make aluminium wire easy to solder. Plan the termination method before choosing the enamel (see the fabrication section below).
IEC 60317-15 (polyesterimide, class 180), IEC 60317-25 (dual coat, class 200) and IEC 60317-89 (polyesterimide, class 200) are examples of the IEC parts written specifically for enamelled round aluminium wire.
The table gives the conductor area and bare mass for preferred nominal diameters in the IEC R20 series. Mass is calculated from a density of 2.70 g/cm³; enamel adds a few per cent depending on grade. Use it to estimate coil weight and to compare spool quantities in a quotation.
| Nominal diameter (mm) | Area (mm²) | Bare mass (kg/km) |
|---|---|---|
| 0.40 | 0.1257 | 0.34 |
| 0.50 | 0.1963 | 0.53 |
| 0.63 | 0.3117 | 0.84 |
| 0.80 | 0.5027 | 1.36 |
| 1.00 | 0.7854 | 2.12 |
| 1.25 | 1.2272 | 3.31 |
| 1.60 | 2.0106 | 5.43 |
| 2.00 | 3.1416 | 8.48 |
| 2.50 | 4.9087 | 13.25 |
| 3.15 | 7.7931 | 21.04 |
| 4.00 | 12.5664 | 33.93 |
| 5.00 | 19.6350 | 53.01 |
Resistance at 20 °C is the resistivity divided by the area: for 1350 annealed wire, roughly 0.028 ÷ area (mm²) ohms per metre. A 1.00 mm wire is therefore about 0.036 Ω/m (36 Ω/km). Correct for operating temperature with the temperature coefficient, which adds about 4 % resistance for every 10 °C rise.
Wire gauges in North America are usually given in AWG and in older British and Indian specifications in SWG. Aluminium wire is drawn to the same gauge tables as copper, so a gauge number refers to the same diameter in either metal; only the resistance and mass per metre differ.
In motors the larger conductor can raise slot fill or reduce turns, which affects efficiency classes under IEC 60034-30-1. Many appliance and fan motors run comfortably on aluminium; premium-efficiency industrial motors more often stay with copper because they need maximum conductivity in a fixed frame size. In distribution transformers both conductors meet the same loss standards; the choice is usually economic.
Aluminium forms a hard, insulating oxide film within seconds of exposure to air. It also creeps under sustained pressure and expands more with heat than copper. A joint that ignores these three facts can loosen and overheat over time.
TIG, resistance, cold-pressure and ultrasonic welding are the most reliable ways to join aluminium winding ends to each other or to copper leads. Friction-welded aluminium-copper transition pieces are common in transformers.
Use connectors designed for aluminium, with serrations that break the oxide and, where specified, an oxide-inhibiting compound. Crimp tooling must be matched to the conductor size.
Possible with special aluminium fluxes and solders or ultrasonic soldering baths that scrub the oxide away. Standard tin-lead or lead-free baths used for copper are not sufficient.
Annealed aluminium is softer than copper, so set winding tension lower, check guide rollers and nozzles for sharp edges, and avoid kinks that thin the conductor.
Keep spools in their packaging in a dry store and use first-in, first-out. Enamel absorbs some moisture; condensation from cold transport should be allowed to clear before winding.
| Standard | Scope |
|---|---|
| IEC 60317-0-3 | General requirements for enamelled round aluminium winding wire |
| IEC 60317 product parts | Individual enamel types and thermal classes, e.g. parts 15, 25 and 89 for aluminium |
| IEC 60851 series | Test methods: dimensions, elongation, springback, flexibility, adherence, heat shock, cut-through, breakdown voltage, continuity |
| NEMA MW 1000 | North American magnet wire standard, including aluminium wire types |
| ASTM B609 | 1350 round wire, annealed and intermediate tempers, for electrical purposes (bare conductor) |
| ASTM B566 | Copper-clad aluminium wire |
| IEC 60085 / IEC 60172 | Thermal classification and temperature index testing of insulation |
A useful order specification states the conductor (1350 annealed), nominal size and tolerance, insulation type and build, thermal class and the governing standard. Ask for a test certificate that reports, per lot, conductor diameter, overall diameter, resistance, elongation, breakdown voltage, pinhole or continuity results and heat-shock results. For transformer conductor, add the proof stress or hardness if the design relies on it for short-circuit strength.
Electrically it does the same job once it is sized correctly: about 1.6 times the copper cross-section gives the same resistance at about half the weight. Copper is preferable where the winding space is fixed and small, or where maximum efficiency in a given frame size is required.
Electrical-conductor grade 1350 (EN AW-1350), and sometimes 1370, supplied fully annealed. These have at least 99.5 % aluminium and a conductivity of about 61 – 62 % IACS. General-purpose alloys are not used because their conductivity is much lower.
Not with an ordinary solder bath. Aluminium oxide prevents wetting, so you need special aluminium solder and flux, ultrasonic soldering, or a welded or crimped joint. Welding to a copper lead is the most common approach in transformers and motors.
CCA has a thin copper layer bonded to an aluminium core. It is slightly heavier and more expensive than solid aluminium but solders like copper and performs a little better at high frequency. For low-frequency power windings, solid aluminium usually offers better value.
Choose a class above the coil hot-spot temperature: class 155 (F) for many appliance motors, class 180 (H) for industrial motors and dry-type transformers, and class 200 (N) or higher for hermetic compressors and heavy-duty service.
Yes. Metline supplies aluminium conductor in wire rod, bare wire, insulated wire, strip and foil to customers worldwide from Mumbai, with test certificates and export packing. Send your specification to sales@metline.in.
Send the conductor size, insulation, thermal class, spool type and quantity. We will confirm availability, the test standard and a delivered price.
