Joining aluminium to copper busbars requires particular care because the two materials behave differently in terms of electrical conductivity, electrochemical potential, and mechanical properties. If the joint is not properly designed, the connection can experience increased resistance, local overheating, corrosion, or in severe cases, failure.
For example, directly welding or bolting the two materials without appropriate mitigation may seem practical, but this approach can lead to problems depending on the exposure to the surrounding environment.
In addition to corrosion, joint performance is often governed more by contact resistance than by the bulk conductivity of the materials, particularly due to the formation of aluminium oxide (Al₂O₃), a stable but electrically resistive surface layer. As a result, even though aluminium performs excellent as a conductor, careful control of the interface is essential to ensure long-term electrical and mechanical reliability in aluminium-copper connections.
Busbars in switchgear, electrical panels and power distribution systems
Let me start out with this simple question: What exactly is a busbar?
Busbars are metallic bars, strips, tubes or rods, that conduct electrical currents from one place to another. They provide efficient power transfer with minimal resistance, while reducing the risk of overheating and short circuits. And by acting as conductive pathways, these metallic components are integral in switchgear, electrical panels and power distribution systems.
Busbars require conductive materials, either copper or aluminium, depending on the requirements of the distribution system. Because it is less conductive than copper, aluminium requires a larger cross-section to be able to match the conductance of the red metal. However, its lower density and cost enable aluminium to provide savings in weight, material usage, carbon footprint and cost.
Both materials are well established and perform effectively in service. While copper continues to dominate many applications, aluminium has a significant and growing share, particularly where weight and cost are critical factors.
Proven methods of joining aluminium to copper busbars
Today, aluminium and copper busbars are connected using established methods that control the interface between the two materials and thereby ensure safe and reliable operation. The five most commonly used methods include:
- Bimetallic transition plates. A bimetallic transition plate, also called bimetallic lugs, transition pads, or copper-aluminium adapters, is factory-bonded with one side copper and one side aluminium, joined using explosion welding, friction stir welding or diffusion bonding. This method is widely accepted as the industry standard. It is performed by bolting an aluminium busbar to the aluminium surface and bolting a copper busbar to the copper surface. This configuration avoids exposing a direct aluminium–copper interface to the environment. As a result, galvanic corrosion is effectively mitigated under normal operating conditions, while maintaining low electrical resistance and excellent long-term stability. This method is widely accepted by switchgear manufacturers and is considered one of the most robust and reliable solutions.
- Tin-plated interfaces. Tin-plated busbar interfaces use a layer of tin plating to create a stable, conductive surface between aluminium and copper, reducing oxidation and controlling galvanic interaction. This method is typically used if a bimetallic transition plate isn't feasible. Although tin does not eliminate the galvanic potential between the two metals, it reduces the effective driving force and creates a more uniform contact interface. Tin also forms relatively conductive surface oxides compared to aluminium, which helps maintain low contact resistance. To be effective, this method requires careful installation. All surfaces must be thoroughly cleaned before assembly, and an oxide-inhibiting joint compound should be applied to exclude moisture and limit oxide formation. Belleville washers or equivalent spring elements are used to maintain consistent contact
- Bolted joints with joint compound. Bolted joints with joint compound rely on an oxide-inhibiting compound, such as Penetrox or Noalox, applied after thoroughly cleaning all contact surfaces. This method is commonly used in field installations but requires strict adherence to installation procedures. Tin-plated hardware or intermediate conductive layers are typically used, in combination with Belleville washers, to maintain adequate contact pressure. Fasteners must be tightened according to manufacturer specifications to ensure consistent performance. While this method does not require specialized equipment, it is more sensitive to installation quality and environmental conditions. There is an increased risk of long-term corrosion and rising contact resistance if the joint is not properly maintained, making periodic inspection necessary.
- Welded bimetallic transitions. This approach is typically used in high-current systems such as enclosed busways or bus ducts. It involves the use of factory-produced bimetallic elements, such as explosion-bonded plates or friction stir welded transitions. Ultrasonic welding may also be used in applications involving thin conductors, such as electric vehicle systems. These solutions provide a permanent metallurgical bond with very low electrical resistance and high mechanical integrity. Environmental exposure of the copper-aluminium interface is prevented, effectively mitigating galvanic corrosion in service. However, they require specialized manufacturing processes and equipment, and are not suitable for field fabrication.
- Compression connectors (crimped bimetal lugs). This method is most commonly used for joining in cables or in systems with high amounts of cables, but it can also be a viable method for smaller busbars. The process involves a bimetal lug being crimped onto the aluminium parts (cables, busbars). The copper part or surface is then bolted to the copper part of the lug. These connectors are reliable and standardized, but their applicability is generally limited by conductor size and system design requirements.
One final point: Before assembling any aluminium–copper joint, all contact surfaces should be properly cleaned and an appropriate anti-oxidation compound applied. This helps limit oxide formation, exclude moisture, and reduce contact resistance, thereby improving the long-term electrical and mechanical stability of the connection.
