Insulated aluminium flat conductor is a solid aluminium alloy bar with continuous insulation, supplied on reels so that busbar makers can straighten, cut, strip, bend and terminate high-voltage connections in-house. It replaces copper busbars and heavy cables in battery packs, junction boxes and the charging path of electric vehicles at roughly half the weight for the same resistance. This guide covers conductor alloys, insulation options, processing and validation.
A high-voltage battery electric vehicle moves hundreds of amps between the battery pack, the battery junction or disconnect unit (BJB / BDU), the inverter and the charging inlet. Rigid busbars carry that current along fixed routes; flexible cables are used where parts move.
Traditionally the rigid links were copper bars, stamped and then insulated one by one with heat-shrink tube or powder coating. A reel-fed insulated aluminium conductor reverses the sequence: the aluminium flat bar is insulated continuously first and supplied on a reel, and the busbar maker cuts it to length, strips the insulation only where the terminals go, and bends it into the final 3D shape. That removes a separate insulation step for every part and suits automated high-volume lines.
Metline supplies the aluminium conductor material. The customer, or the customer's busbar supplier, carries out forming, termination and assembly, so the material has to be specified around that downstream process as well as around electrical performance.
Aluminium conducts about 61 % as well as copper by volume, so a conductor needs a larger cross-section to reach the same resistance: about 1.64 times larger when comparing electrical-grade aluminium with annealed copper. Because aluminium is less than a third as dense, the larger aluminium bar still weighs about half as much. The table works this through for common copper sizes, using resistivity ratio and density only.
| Copper section (mm²) | Aluminium section for equal resistance (mm²) | Copper mass (kg/m) | Aluminium mass (kg/m) |
|---|---|---|---|
| 50 | 82 | 0.44 | 0.22 |
| 70 | 115 | 0.62 | 0.31 |
| 95 | 156 | 0.84 | 0.42 |
| 120 | 197 | 1.07 | 0.53 |
| 150 | 246 | 1.33 | 0.66 |
Calculated with 2.82 µΩ·cm for EC-grade aluminium, 1.72 µΩ·cm for annealed copper, and densities of 2.70 and 8.89 g/cm³. 6101 alloys have slightly lower conductivity than EC-grade aluminium, so add a margin and confirm with temperature-rise tests.
The penalty is space: the aluminium bar is wider or thicker. In practice designers often use the extra width as a cooling surface, because a flat bar sheds heat well. Where packaging space is tight, copper or copper-clad aluminium may still be the right choice for a short link.
Most insulated aluminium busbars use 6101, a heat-treatable Al-Mg-Si alloy developed for electrical conductors. It combines conductivity of roughly 55 – 60 % IACS with much higher strength than pure EC-grade aluminium, which matters when a bar has to hold its bent shape, carry bolt loads and survive vibration. ASTM B317 covers 6101 extruded bus conductor in several tempers.
| Temper | Treatment | Balance of properties | Typical use |
|---|---|---|---|
| 6101-T61 | Solution treated and over-aged for conductivity | High conductivity, moderate strength, good formability | Busbars that are bent in several planes |
| 6101-T63 | Aged for higher strength | Higher strength, slightly lower conductivity | Long unsupported spans, bolt-loaded terminals |
| 6101-T64 | Aged for maximum conductivity | Highest conductivity and best bendability, lowest strength | Current-dense links with tight bends |
| 6101-T65 | Intermediate ageing | Balanced strength and conductivity | General high-voltage routing |
| 1350 / 1060 (alternative) | Non-heat-treatable pure grades | About 61 – 62 % IACS, low strength | Supported routes where bend retention is less critical |
Minimum conductivity and strength for each temper are set by the applicable standard and the project specification and are reported on the mill certificate.
A continuous extruded jacket of PA12, PVC, PE or another polymer, typically from about 0.5 mm thick, chosen for dielectric strength, temperature class, abrasion resistance and how cleanly it strips. Suited to standard high-voltage routing inside the pack and junction box.
The aluminium core is wrapped with a fire or thermal barrier layer (for example mica-based or ceramifying materials) under an outer polymer jacket. Intended for bars that run close to cells or modules where flame or high heat from a thermal event must not cause a short circuit.
Heat-shrink tubing, powder epoxy coating or dip coating applied after forming. These suit low volumes or complex 3D parts but add a separate process for each part.
| Engineering situation | Insulation to evaluate first |
|---|---|
| Standard high-voltage routing where insulation, current and weight are the priorities | Polymer insulated |
| Dense BJB / BDU interfaces with many bends, strips and terminals | Polymer insulated |
| Routing next to cells, modules or another defined heat source | Fire-resistant thermal-barrier composite |
| Project requires a fire-resistance or thermal-barrier test on the busbar | Fire-resistant thermal-barrier composite |
| One route crosses zones with different thermal risk | Design to the highest-risk zone along the route |
| On-vehicle charging inlet to battery path | Decide from charge current, terminal temperature rise and surrounding heat |
Flame retardancy, fire resistance and thermal insulation are different properties. A material rating for flammability (for example UL 94) does not show that the complete bar keeps its insulation during a flame or thermal-runaway exposure; that has to be tested on a formed sample with the project's temperature, duration and measuring point.
A typical line runs: reel feeding, straightening, cutting to length, stripping, bending or forming, and terminal preparation. Each step puts its own demands on the material.
| Check | What to look for | Applies to |
|---|---|---|
| Bend integrity | No cracking, whitening, wrinkling or thinning of the insulation at bends | All types |
| Strip and terminal condition | Clean strip boundary, no residue on contact faces, no conductor nicks | All types |
| Dielectric withstand and insulation resistance | Pass the voltage and resistance levels set by the OEM specification | All types |
| Formed dimensions | Critical interfaces and hole positions within drawing tolerance | All types |
| Resistance and temperature rise | Joint resistance and temperature rise under rated continuous and peak current | All types |
| Layer continuity | No delamination; barrier layer continuous through bends | Composite type |
| Thermal or flame exposure | Insulation maintained for the required time on a formed sample | Composite type |
New projects normally start with samples built to the agreed conductor, insulation and reel configuration, which the customer runs through its own equipment and tests. Once approved, that configuration becomes the supply baseline, with reel or batch traceability, inspection records and an agreed change-control process for any material or process change.
There is no single value. It depends on the temper, the width-to-thickness ratio, whether the bend is flatwise or edgewise, the angle and the insulation material, and it should be confirmed by bending real samples on your equipment.
It should, but that must be proved on formed samples: check that the barrier layer stays continuous and undamaged through the bends and then run the thermal or flame test on the formed part.
It is removed locally by laser or mechanical stripping. The strip position, length, boundary quality and allowable residue are defined on the drawing, and contact faces are usually plated.
6101 keeps conductivity close to pure aluminium while giving much higher strength, so bent busbars hold their shape, resist vibration and carry bolt loads better.
Yes. For equal resistance the aluminium section is about 1.6 times larger, but because aluminium is about a third of the density of copper the bar weighs roughly half as much.
Mill test certificates with chemistry and properties, dimensional inspection records, agreed performance test results and reel or batch traceability. Additional automotive project documents are agreed at project start.
Send the application, drawing or target cross-section, insulation requirement and volume. We will review it and reply with a supply proposal.
