What is Cuponal and How Does Bimetal Cladding Actually Work?

If you work with power distribution, switchgear, or high-current assemblies, you have probably heard the word ‘Cuponal’ mentioned in a design meeting or on a bill of materials.

It usually comes up when someone wants the surface benefits of copper but also wants to reduce weight and keep budgets under control by using aluminium where it makes sense.

At ILF, we get questions about Cuponal all the time. So, here’s a straightforward guide to what it is, how it is made, and what to watch out for when specifying it on real projects.

A Quick Definition

Cuponal is copper-clad aluminium. That means you have a copper outer layer that is metallurgically bonded to an aluminium core, creating a single composite material.

Bimetal cladding is the broader term. It simply means two different metals are permanently joined to create one combined section.

Why do Engineers use Cuponal?

Most people choose Cuponal for a practical reason: it can give you a useful balance of performance and handling.

In many electrical applications, the current tends to concentrate nearer the surface of the conductor. With Cuponal, the copper layer is doing a lot of the work electrically, while the aluminium core helps reduce overall mass. Done properly, it can be a sensible option when space is tight, weight matters, or you are looking for alternatives to solid copper.

You will often see Cuponal used in:

• Busbar systems and distribution boards.
• Earthing and bonding arrangements.
• Risers and rising mains.
• Transformer links and connectors.

How Does Bimetal Cladding Work?

The important thing to know is that Cuponal is not “glued together”.

The copper and aluminium are combined continuously using pressure and diffusion, creating a metallurgical bond at the interface. That bond is designed to resist peeling and separation under normal service conditions.

In plain terms, it behaves like a single piece of material in everyday use, rather than two layers that can easily split apart.

What Should you Consider when Specifying Cuponal?

This is where experience matters, because most problems with bimetal products are not caused by the material itself. They are usually caused by the way it is connected, supported, or protected in the real world.

1) Jointing and dissimilar metals

Copper and aluminium are dissimilar metals, so you always want to think about corrosion risk if moisture can get involved.

A good Covalent bond is tight and formed to minimise voids. That helps reduce pathways for electrolytes to enter the interface. In installation, correct joint design and suitable contact compounds can also help reduce risk, especially in environments where condensation or contamination may be present.

2) Thermal behaviour and connection reliability

Copper and aluminium expand differently with temperature changes. On high-current systems, this can influence joint pressure over time if the assembly is not designed well.

Good results come from getting the basics right:

• Choose the right section size for duty and fault conditions.
• Make sure joint faces are clean and correctly prepared.
• Use appropriate hardware and torque settings.
• Support long runs properly and allow for movement where required.

3) Processing and fabrication

Cuponal is commonly drilled, punched, sawn and bent in similar ways to copper bar, but the key is to protect the integrity of the cladding and keep contact areas in good condition.

If you are replacing an existing solid copper busbar with a composite alternative, it is worth checking the full assembly details early, including terminations, clearances, enclosure conditions, and how the joints will be maintained over time.

Advantages and Limitations, Explained Simply

Advantages

• Reduced weight compared with solid copper in many equivalent designs.
• A copper surface can support good termination behaviour and low contact resistance.
• Can help manage material cost exposure in copper-heavy builds.

Limitations

• Jointing needs the right method and attention to surface preparation.
• Incorrect hardware choices can increase heating at connections.
• Bend radii and support spacing matter if you want long-term reliability.

A Practical Note from the Shop Floor

If there is one theme we see again and again, it is this: most electrical issues start at the joint.

A well-designed busbar is only as good as its terminations, supports, and installation quality. A quick check of joint design, contact faces, torque procedures, and environmental protection can save a lot of downtime later.

If you are ever unsure, it is better to ask early and confirm what is achievable with your chosen materials, section sizes, and build constraints.

FAQ: Common Searches and Questions we Hear

What is Cuponal?

Ans: Cuponal is a copper-clad aluminium bimetal, where copper is metallurgically bonded to an aluminium core.

Is Cuponal the same as copper clad aluminium (CCA)?

Ans: In most electrical contexts, yes. You will often see Cuponal described as a type of CCA product, particularly when used for busbars.

How does bimetal cladding work?

Ans: The two metals are bonded using controlled processes such as pressure and diffusion (and, in some manufacturing routes, hydrostatic pressing). The aim is a permanent metallurgical join rather than an adhesive layer.

Can you connect copper to aluminium directly?

Ans: Direct copper-to-aluminium contact in dampness increases corrosion risk. To limit service risk, designers employ appropriate connectors, plating schemes, and joint protection. 

Is Cuponal suitable for busbars?

Ans: Yes, it is commonly used for busbar systems where designers want a balance of copper surface properties with improved weight handling, subject to correct specification and jointing.

Cuponal vs copper busbar: which is better?

Ans: Depending on the job. Max conductivity and long-term performance are frequently prioritised with solid copper. Cuponal is good for weight, handling, and material efficiency. The best choice depends on workload, enclosure circumstances, jointing approach, and installation cost.

Want a quick stock and lead time check?

Ans: If you are pricing a build, replacing a busbar run, or planning an upgrade, we can help you confirm what is available and how quickly you can get it.

Ask us for a stock and lead time check on:

• Copper products (bar, profiles, busbars)
• Aluminium products (including common engineering alloys and busbars)
• Cuponal and other bimetal options, where appropriate

Call 01543 226816 or email sales@ilfproducts.co.uk

and let us know what sizes, quantities, and cut or fabrication requirements you are working with. If you have drawings, sharing those upfront helps us move faster.