How to Specify Flexible Copper Busbars for Battery Racks and PCS

A flexible laminated copper busbar is a compact high-current connection made from multiple thin copper foils arranged into a flexible stack, with rigid terminal areas at the connection points. In battery energy storage systems, this structure is especially useful where high current, limited installation space, vibration, assembly tolerance, and thermal movement must all be managed at the same time.

For BESS engineers and sourcing teams, the challenge is not simply choosing “a copper busbar.” A production-ready specification needs to define the electrical load, available installation envelope, required flexibility, terminal geometry, surface finish, insulation, and operating environment.

This guide explains how to turn those requirements into a practical specification for battery racks, power conversion systems (PCS), switchgear, and other high-current DC assemblies.

What Are Flexible Copper Busbars for Battery Racks?

Within a battery rack, flexible laminated copper busbars can connect battery modules, rack-level distribution points, disconnect devices, contactors, or the DC interface leading toward the PCS.

Unlike a rigid solid busbar, the conductive section is formed from multiple thin copper foils. This allows the connection to accommodate limited movement between two terminals while retaining a compact, flat geometry.

In many designs, the terminal regions are consolidated into rigid connection zones so that holes and bolted interfaces can be accurately positioned. The exact terminal construction and manufacturing process should, however, be confirmed against the supplier's production method and the approved drawing.

The important point is that the busbar should be designed around the actual BESS assembly rather than selected as a generic off-the-shelf conductor.

Where Do Flexible Laminated Busbars Fit in a BESS?

A typical battery energy storage system contains several different high-current connection environments.

Inside the battery rack, compact geometry is usually important because modules, protection devices, sensing circuits, and structural components compete for space. Between a rack and a DC distribution point, the connection may need to accommodate assembly tolerance or relative movement. At the PCS interface, current, thermal conditions, terminal geometry, and installation space may become even more demanding.

These positions may all use flexible copper connections, but they do not necessarily require the same cross-section, foil structure, terminal design, or insulation system.

For that reason, a flexible busbar should be treated as a drawing-based electrical component, not simply a copper strip with two holes.

Why Use Flexible Busbars in Battery Rack Connections?

Copper expands and contracts as temperature changes. Battery racks, enclosures, terminals, and support structures may also move slightly during transportation, installation, thermal cycling, or operation.

A rigid connection transfers more of this movement directly into the bolted interfaces. A flexible laminated section can absorb part of that displacement, helping reduce mechanical stress at the terminals.

This makes flexible busbars particularly useful when the design needs to accommodate:

thermal expansion between connected components;

minor terminal misalignment or assembly tolerance;

vibration from transportation or operating equipment;

compact routing within a restricted enclosure;

high-current connections where a large cable bend radius would be inconvenient.

Flexibility should still be engineered rather than assumed. The required direction and amount of movement should be defined on the drawing wherever possible.

Flexible Laminated Busbar vs Cable

Both cables and laminated busbars can carry high DC current, but they solve different packaging and connection problems.

Neither solution is universally better.

Inside battery racks and PCS cabinets, laminated busbars can offer a clean, repeatable connection geometry. For longer cable runs or locations requiring substantial multidirectional movement, cable may be more practical.

Flexible copper braid provides another option where very high mechanical flexibility is required.

What Copper Material Should You Specify?

The conductor material should be clearly stated on the drawing or purchasing specification.

For AVANTAR projects, T2 copper or another project-specified copper grade can be considered depending on conductivity requirements, customer standards, and manufacturing compatibility.

Rather than relying only on a nominal purity value, engineering and sourcing teams should confirm the actual material specification and request appropriate material documentation when required.

Copper conductivity directly influences resistive losses and temperature rise. The Copper Development Association's published busbar data also demonstrate that ampacity depends on more than conductor cross-section alone: dimensions, spacing, surface condition, temperature rise, and cooling conditions all matter. copper.org

How Should Foil Thickness and Layer Count Be Selected?

There is no single foil thickness suitable for every flexible busbar.

Thinner foils generally allow greater flexibility, while thicker foils can produce a stiffer assembly with fewer layers. The final stack should balance:

foil flexibility, total conductor cross-section, terminal construction, required movement, manufacturing process, available installation space, and thermal performance.

Instead of specifying foil thickness based only on a generic online recommendation, provide the electrical and mechanical requirements and allow the proposed construction to be reviewed during drawing approval.

How Should Busbar Size Match Battery Current?

Current is an important starting point, but current alone does not determine the final busbar size.

A preliminary electrical relationship can be written as:

Required copper area ≈ continuous current ÷ preliminary current-density assumption

This can be useful during early packaging studies, but the assumed current density is not a universal design rule.

Final allowable current depends on:

ambient temperature, enclosure airflow, conductor geometry, copper grade, surface condition, terminal design, nearby heat sources, allowable temperature rise, duty cycle, and applicable assembly requirements.

For example, a 250 kW DC rack operating at 1,000 V would draw approximately:

250,000 W ÷ 1,000 V = 250 A

That gives the engineer a starting current, but it does not by itself determine the final width and thickness.

The next step is to evaluate the actual thermal and mechanical design.

Where the busbar forms part of a low-voltage switchgear or controlgear assembly, the applicable IEC 61439 requirements may also need to be considered at assembly level. IEC 61439-1 covers construction and verification requirements for low-voltage assemblies and includes DC and temperature-rise considerations; it should not be described as a standalone certification for an individual custom busbar. IEC Webstore

Check the Terminal Area, Not Only the Middle Section

One common mistake is sizing only the flexible copper stack while ignoring the terminal.

Bolt holes remove conductive material. Narrow areas around holes, slots, bends, or formed terminals can therefore become thermal bottlenecks.

The drawing should be reviewed for:

net copper section around holes, terminal width, hole-to-edge distance, mating contact area, bolt arrangement, surface finish, and mechanical support.

The connection interface is part of the electrical design.

How Much Flexibility Does a PCS Connection Need?

A PCS connection may need to accommodate several forms of movement at once.

Instead of specifying a vague requirement such as “highly flexible,” define the movement the connection actually needs.

Useful drawing inputs include lateral displacement, axial movement, angular movement, available free length, preferred bend direction, and the minimum available installation envelope.

Do not copy a standard offset value from another project. A busbar connecting two rigid terminals 150 mm apart has a very different mechanical requirement from one spanning a larger gap between independently mounted assemblies.

The flexible section should be engineered around the actual geometry.

How Should Insulation Be Specified?

Insulation should be selected according to the electrical system and the actual material grade being used.

Possible solutions include heat-shrink systems, polymer sleeves, insulating films, or other project-specific constructions.

Do not specify temperature capability simply by writing “PVC,” “heat shrink,” or “polyimide.” Different grades of the same material family can have different electrical, thermal, flammability, thickness, and environmental characteristics.

A useful insulation specification should therefore define:

material or approved material family, rated voltage or dielectric requirement, required operating temperature, insulation thickness where relevant, color, exposed terminal length, and any project-specific flammability or environmental requirement.

What Terminal Details Belong on the Drawing?

The terminal interface should be fully dimensioned.

For bolted BESS and PCS connections, the drawing should normally identify hole diameter, hole quantity, center-to-center spacing, edge distance, terminal width, terminal length, thickness, required bends, and mating hardware information where relevant.

Surface finish should also be stated.

Common options include bare copper, tin, or silver, depending on the contact interface, corrosion environment, performance requirement, and customer specification.

Avoid automatically specifying a particular plating simply because the current is high. The finish should be chosen as part of the overall connection design.

What About UL, CE, and Other Compliance Requirements?

Compliance requirements should be defined project by project.

UL 486A-486B is a standard for wire connectors and specific connector applications. It should not automatically be presented as a general certification requirement for every custom laminated busbar. If a project requires UL-related performance, the scope and applicability should be checked against the exact product and connection design. UL Standards Online

The same principle applies to CE marking.

CE marking is mandatory only for products that fall within the scope of applicable EU legislation; the European Commission explicitly states that not all products require CE marking, and CE should not be applied to products outside the relevant legislative scope. 内部市场、工业与创业

For this reason, a professional busbar specification should identify the actual project compliance requirements rather than listing ISO 9001, CE, RoHS, or UL as a universal package.

How Should Temperature Rise Be Verified?

Preliminary calculations help establish a starting geometry. Testing or validated thermal analysis provides greater confidence in the final design.

For a new high-current connection, a temperature-rise evaluation may include:

mounting the busbar between representative terminals, applying the required current, monitoring temperature until a stable condition is reached, and measuring critical locations such as the flexible section, terminal region, and bolted interface.

The test configuration should represent the actual installation as closely as practical.

Enclosure temperature, airflow, conductor orientation, terminal torque, neighboring heat sources, and insulation can all influence the result.

What Should a Flexible Busbar Specification Include?

A good RFQ should give the supplier enough information to quote and prepare an approval drawing without repeatedly asking basic engineering questions.

Electrical requirements: continuous current, peak or overload current if relevant, system voltage, duty cycle, target temperature rise, and known short-time current requirements.

Installation envelope: maximum length, width and thickness, available space around the connection, and the position of the two mating terminals.

Required movement: lateral, axial or angular displacement that the flexible section must accommodate.

Conductor requirements: copper grade if specified, preferred foil construction where already defined, and any customer material standard.

Terminal geometry: hole diameter, hole quantity, center spacing, edge distance, terminal dimensions, bend geometry, and interface drawing.

Surface treatment: bare copper, tin, silver, or another approved finish based on the project requirement.

Insulation: material requirement, rated voltage, temperature requirement, color, coverage area, and exposed terminal length.

Operating environment: ambient temperature, enclosure conditions, humidity, corrosion exposure, cooling conditions, and relevant environmental requirements.

Documentation: dimensional drawing, material documentation, inspection requirements, testing requirements, and any project-specific compliance documents.

Drawing files: a dimensioned 2D drawing and, where available, a STEP or other 3D file.

Providing this information early makes it much easier to turn an engineering concept into a production-ready component.

A Practical Specification Example

Consider a BESS designer who already knows the rack current and terminal locations but has not finalized the busbar.

Instead of sending:

“Need flexible busbar for 500 A.”

A much better RFQ would define:

Application: BESS rack DC connection
Continuous current: project value
System voltage: project value
Terminal center distance: according to drawing
Available width and thickness: defined installation envelope
Required movement: specified lateral/axial tolerance
Terminal holes: drawing-defined
Surface finish: project requirement
Insulation: project requirement
Operating ambient: site or enclosure value
Drawing: attached

This gives the supplier enough engineering context to propose a construction for review rather than guessing from current alone.

FAQ

What is the difference between a flexible laminated busbar and a copper braid connector?

A laminated flexible busbar uses stacked flat copper foils and normally provides a controlled, low-profile connection geometry. Copper braid uses interwoven strands and generally allows greater multidirectional movement. Laminated busbars are often well suited to battery racks, PCS and switchgear power connections, while braid can be useful where greater mechanical flexibility is needed.

How do I calculate flexible busbar size for a battery rack?

Start with continuous operating current, then consider temperature rise, ambient temperature, airflow, enclosure conditions, conductor geometry and terminal design. A current-density calculation can be used for preliminary sizing, but the final cross-section should be verified against the real thermal and installation conditions.

Which surface finish should I use for BESS busbars?

There is no single finish for every application. Bare copper, tin and silver may all be appropriate depending on the mating terminal, corrosion environment, contact requirements and customer specification. The finish should be selected as part of the complete connection design.

Can AVANTAR manufacture from a customer drawing?

Yes. AVANTAR supports drawing-based supply of flexible laminated copper busbars. Customers can provide electrical requirements together with 2D or 3D drawings covering dimensions, terminal geometry, surface treatment, insulation and installation constraints for technical review.

What information should I send before requesting a quotation?

At minimum, provide continuous current, system voltage, approximate dimensions or installation space, terminal-hole arrangement, required flexibility or movement, preferred surface finish, insulation requirement and the operating environment. A dimensioned drawing is strongly recommended.

Conclusion

Specifying a flexible laminated copper busbar for a battery rack or PCS is not simply a question of choosing copper width and thickness.

A production-ready design should define the electrical load, installation envelope, required movement, terminal interface, surface finish, insulation, and operating environment.

Preliminary calculations are useful during early design, but final geometry should be verified against temperature rise, actual assembly conditions and the applicable project requirements.

For BESS projects, this approach gives engineering and procurement teams a much stronger basis for comparing proposals and approving a repeatable production part.

Turn Your Busbar Drawing Into a Production-Ready Part

AVANTAR supplies drawing-based flexible laminated copper busbars for BESS, battery racks, PCS, switchgear and other high-current power connections.

Send your current requirement, installation dimensions and 2D/3D drawing to:

[email protected]

Our team can review the required geometry, terminal interface, surface finish, insulation and project documentation requirements before quotation.

AVANTAR
AVANTAR (GUANGDONG) INDUSTRIAL HOLDINGS CO., LTD.