Coiled aluminium busbar is flat or shaped conductor wound into coils instead of cut into straight lengths, so that it can be fed continuously into straightening, cutting, punching and bending lines. It is made in high-conductivity 1xxx grades such as 1350, 1060 and 1070, and in heat-treatable 6101 where more strength is needed. This guide covers alloys, tempers, conductivity, sizes, insulation and how to decide between coil and straight bar.
A busbar is a solid conductor that carries large currents between components: from a transformer to switchgear, between battery cells, or along a distribution run. Supplying it as a coil rather than as 3 – 6 m straight bars changes how it is processed, not what it is.
Busbar fabricators traditionally buy straight bar, cut it to length, then punch and bend each piece. That works for low volumes, but high-volume production of battery-pack connectors, switchgear links, motor and inverter conductors or busway sections favours a continuous process. A coil can be loaded on a pay-off reel, straightened in-line and fed into a progressive tool or CNC bender that produces finished parts at a constant rate, with only a few metres of offcut per coil instead of an offcut at the end of every bar.
Coiled busbar is possible only because high-conductivity aluminium is soft and ductile in its as-fabricated or lightly worked condition. It can be wound on a drum without cracking, then straightened back to a flat, consistent bar. Heat-treatable 6101 is also supplied in coil in tempers chosen to keep enough ductility for coiling and later bending.
Two manufacturing routes produce coiled busbar, and the route decides which cross-sections and sizes are practical.
Electrical-grade rod is rolled or drawn through shaped rolls into a rectangular section and wound into coils. Typical products are 1350, 1060 and 1070 in the H112 or similar as-fabricated condition, from roughly 2 – 10 mm thick and 5 – 100 mm wide. Edges can be rounded to reduce field concentration and protect insulation.
Feedstock rod is gripped in the groove of a rotating wheel, heated by friction and forced through a die. The process runs without stopping, so it produces very long lengths with uniform properties. It suits rectangular, obround and round sections in 1xxx grades and 6101, and wider conductors with cross-sections of several hundred mm².
Billet is pressed through a die on a hydraulic press. It makes complex profiles and large sections but in finite lengths, so it is normally used for straight busbar rather than long coils.
Both continuous routes give clean, dense conductors with close dimensional control. The practical difference for buyers is that continuous extrusion can produce shaped and larger sections, while rolled flat conductor is usually the economical choice for standard rectangular sizes.
Electrical conductivity is the main selection criterion, followed by strength, formability and resistance to creep at bolted joints. Conductivity is expressed as a percentage of the International Annealed Copper Standard (% IACS), where annealed copper is 100 %.
| Alloy | Type | Typical conductivity | Strength | Typical use |
|---|---|---|---|---|
| 1350 (EC grade) | Al ≥ 99.50 %, impurities that harm conductivity tightly limited | About 61 – 62 % IACS | Low | Power distribution, switchgear, busway, transformer leads |
| 1370 | Al ≥ 99.70 %, electrical grade | About 61 – 62 % IACS | Low | High-conductivity conductors made by continuous extrusion |
| 1060 | Al ≥ 99.60 % | About 61 – 62 % IACS | Low | General electrical bar, battery connectors |
| 1070 | Al ≥ 99.70 % | About 61 – 62 % IACS | Low | Connectors where conductivity is the priority |
| 6101 | Al-Mg-Si, heat-treatable | About 55 – 60 % IACS, depending on temper | Medium | Conductors that must carry mechanical load, EV and charging conductors |
Conductivity values for 1xxx grades are typical figures for the soft or as-fabricated condition. Specified minimums depend on the order standard and temper; the mill certificate reports measured conductivity for each lot.
The 1xxx grades are effectively pure aluminium. Their conductivity is high but their strength is low, so they are used where the conductor is well supported and does not carry mechanical load. 6101 adds small amounts of magnesium and silicon; heat treatment produces fine precipitates that raise strength, with a small loss of conductivity. Choosing the temper lets the designer move along that trade-off.
ASTM B317 covers 6101 extruded bar, rod, tube and profiles for electrical conductors. The minimum properties below are the values commonly published for thin sections (about 3 – 12 mm); thicker sections have lower strength minimums in some tempers.
| Temper | Min. tensile strength | Min. yield strength | Min. conductivity | Character |
|---|---|---|---|---|
| 6101-T6 | 200 MPa (29 ksi) | 172 MPa (25 ksi) | 55.0 % IACS | Strongest, lowest conductivity |
| 6101-T63 | 186 MPa (27 ksi) | 152 MPa (22 ksi) | 56.0 % IACS | High strength, slightly better conductivity |
| 6101-T65 | 172 MPa (25 ksi) | 138 MPa (20 ksi) | 56.5 % IACS | Balanced strength and conductivity |
| 6101-T61 | 138 MPa (20 ksi) | 103 MPa (15 ksi) | 57.0 % IACS | Good conductivity with moderate strength |
| 6101-T64 | 103 MPa (15 ksi) | 55 MPa (8 ksi) | 59.5 % IACS | Highest conductivity and best formability |
For coiled conductors that will be bent tightly after straightening, T61 or T64 is usually the starting point because their higher elongation tolerates coiling and forming. Where the conductor must support itself or resist vibration, T63, T65 or T6 gives more strength. Typical delivered values are often better than these minimums; design to the minimums and check the certificate.
The table lists common rectangular sizes with weight and calculated DC resistance at 20 °C. Resistance is calculated from the cross-section and the stated conductivity, ignoring corner radii, so treat it as a planning figure rather than a guaranteed value.
| Size (t × w, mm) | Area (mm²) | Weight (kg/m) | DC resistance at 61 % IACS (µΩ/m) | DC resistance at 57 % IACS (µΩ/m) |
|---|---|---|---|---|
| 3 × 20 | 60 | 0.162 | 471 | 504 |
| 3 × 25 | 75 | 0.203 | 377 | 403 |
| 3 × 40 | 120 | 0.324 | 236 | 252 |
| 4 × 30 | 120 | 0.324 | 236 | 252 |
| 4 × 40 | 160 | 0.432 | 177 | 189 |
| 5 × 30 | 150 | 0.405 | 188 | 202 |
| 5 × 50 | 250 | 0.675 | 113 | 121 |
| 6 × 60 | 360 | 0.972 | 79 | 84 |
| 8 × 80 | 640 | 1.728 | 44 | 47 |
| 10 × 100 | 1000 | 2.700 | 28 | 30 |
Exact size combinations depend on alloy, temper and route; confirm with your enquiry.
Aluminium is replacing copper in many busbar systems because of weight and cost, but it cannot be swapped at the same dimensions. The physics is straightforward:
| Property | Copper (C11000) | Aluminium 1350 | What it means |
|---|---|---|---|
| Conductivity | About 100 % IACS | About 61 % IACS | Aluminium needs about 1.6 × the cross-section for the same resistance |
| Density | 8.89 g/cm³ | 2.70 g/cm³ | Aluminium is about 30 % of copper by volume weight |
| Mass for equal resistance | 1.0 | About 0.5 | An equal-resistance aluminium bar weighs roughly half |
| Thermal expansion | 17 µm/m·°C | 23 µm/m·°C | Joint design must allow for greater movement |
| Oxide film | Conductive oxide | Hard insulating oxide | Contact surfaces need preparation or plating |
| Creep at joints | Low | Higher | Use spring washers and correct torque, or harder alloys |
Because the aluminium bar is larger, it also has more surface to shed heat, which helps temperature rise. The design should be checked for the actual current, permitted temperature rise, ambient temperature and available space rather than by converting a copper size directly.
Polyamide (PA12), PVC, polyethylene or other polymers can be extruded continuously over the conductor. PA12 is common for EV high-voltage conductors because of its toughness and temperature rating.
Epoxy powder or dip coatings insulate cut and bent parts, leaving contact areas bare for bolting.
Plating the contact areas gives stable, low contact resistance and protects against galvanic corrosion when bolted to copper terminals.
Clean the contact face to remove oxide, apply a suitable contact compound, and use spring (Belleville) washers so the joint keeps its clamping force as aluminium creeps and cycles thermally.
TIG, MIG, friction stir, laser and ultrasonic welding join aluminium busbar without bolts. Ultrasonic and laser welding are widely used for battery cell connections.
Where aluminium meets copper, use plated contacts or bimetallic transition pieces to prevent galvanic attack in humid environments.
| Situation | Better choice | Reason |
|---|---|---|
| Automated stamping or CNC bending at volume | Coil | Continuous feed, fewer changeovers and less offcut |
| Many part lengths from one section | Coil | Cut to exact part length instead of nesting in fixed bars |
| Long unbroken conductor runs | Coil | Avoids joints and splices |
| Small batches or prototypes | Straight | No straightening equipment needed |
| Thick, wide or high-strength sections | Straight | Too stiff to coil and straighten without residual curvature |
| Long straight runs used as cut | Straight | Simpler handling, no straightening step |
A common mistake is to order coiled conductor without checking the straightener and pay-off capacity. Coil inner diameter, outer diameter, weight and winding direction must suit the line, and the temper must be soft enough to straighten without leaving a set.
High-conductivity grades 1350, 1370, 1060 and 1070 for most distribution and connector work, and 6101 in tempers such as T61, T63, T64 and T65 where more strength is needed.
About 61 – 62 % IACS for 1xxx grades and about 55 – 60 % IACS for 6101 depending on temper. ASTM B317 minimums for 6101 range from 55.0 % IACS (T6) to 59.5 % IACS (T64).
For the same DC resistance, about 1.6 times the cross-section of a copper bar. It will still weigh roughly half as much as the copper bar.
Yes. Insulation such as PA12, PVC or PE can be extruded over the conductor, or bare coil can be supplied for coating after forming. Specify the insulation material, thickness and temperature rating.
Soft 1xxx grades and ductile 6101 tempers straighten well on a suitable roller straightener. Very thick or high-strength sections are better ordered straight.
Conductivity can be measured with an eddy-current meter or by resistance testing and reported on the mill test certificate, together with dimensions and tensile results.
Send your section, alloy, coil limits and insulation needs. We will propose a suitable conductor and send a delivered quotation.
