In electrical systems, the materials that make up the conductors and connectors are paramount to the effectiveness of power distribution, its longevity and safety. One of the most common challenges to this, in real life, is the connection of dissimilar metals, specifically aluminium and copper. Aluminium and copper are both popular conductors, frequently used throughout the electrical industry. However, they do not connect well with each other when directly connected. This is where bimetallic lugs become important.
Let us explore such lugs and when they should be used.
What Are Bimetallic Lugs?
Bimetallic cable lugs are electrical connectors that connect an aluminium conductor to a copper terminal or busbar. As the name suggests, these consist of aluminium and copper, which are two different metals, joined in one device. Primary aluminium is usually the barrel where the conductor is positioned and crimped, while the primary copper is the palm where the flat terminal end is fastened to copper equipment.
Alloy fittings for aluminium to copper have been around for a long time and almost always join the two metals through a solid-state welding process that is frequently friction welded. Friction welding and process results in a permanent join between the aluminium and copper portion of the lug without a filler material like solder. Depending on the bimetal lug manufacturer, friction welding uses one of three basic approaches to join the aluminium to the copper:
Electrical continuity and mechanical retention are essential features when designing lugs using aluminium or aluminium alloy as the conductive element. Bimetallic lugs and similar approaches were designed to minimise problems that generally arise with an aluminium-to-copper contact.
Bimetallic terminal lugs are not simply to “bridge” two conductors together; they provide a safe, stable interface that respects the design differences that exist with aluminium versus copper, such as their physical properties, their respective thermal expansion coefficients, conductivities, tendency to corrode, and reactivity to moisture or air.
When should you use bimetallic lugs?
To understand what bimetal cable lugs are needed for, we have to first understand the fundamental issue that they address: the problems associated with aluminium and copper when they are directly connected.
When two dissimilar metals are connected together and exposed to an electrolyte (like moisture in the air), a galvanic reaction can happen. With aluminium and copper, aluminium is the anode, meaning that it will corrode faster than it would otherwise.
There are also thermal expansion differences. Aluminium and copper do not expand and contract at the same rate when temperature changes. Over time, these differences can cause loosening of connections, micro-movements, causing arcing or fires.
Most common uses of bimetallic cable lugs
Bimetallic lugs aren’t used in all electrical connections—they’re only needed when aluminium conductors need to interface with any copper-based devices. These circumstances occur in a variety of applications, from residential wiring to industrial power.
The following are the most common cases in which a mix of copper and aluminium lugs is essential:
Aluminium conductors with copper terminals
Many electrical installations, particularly in instances where cost or weight are important considerations, use aluminium cables instead of copper. Aluminium is lighter and less expensive, making it an attractive electrical option for long-distance power distribution. However, most electrical equipment, such as circuit breakers, switchgear, relays, transformers, panels, etc, are manufactured with copper-type terminals or busbars.
You cannot simply connect an aluminium cable directly to a copper terminal with no bimetallic connection plate due to metallurgical compatibility concerns. With bimetallic lugs, you have a solid connection when the aluminium cable is inserted into an aluminium barrel while the copper palm is bolted onto the copper terminal or busbar, thus ensuring a stable interface.
Solar Energy Systems
The size of most solar installations means that aluminium cable is a very prevalent option for feeder lines in a solar array because of its lighter weight and attractive cost. Because most inverters, charge controllers, and distribution panels will have copper terminals, this difference must be addressed.
Bimetal cable lugs are used to join these aluminium cables with copper terminals in solar power installations, which is critical in achieving a long-term, reliable system and meeting the outdoor and variable weather conditions of typical solar farms or rooftop systems.
Industrial and Commercial Power Distributed Boards
It is common in a factory, commercial building, and large infrastructure projects characterised by commercial power distribution boards to have a combination of copper and aluminium wiring depending on design guidelines, space limitations, cost factors or load.
If aluminium conductors are installed entering into distribution boards with copper busbars or copper lugs in terminals, the electric circuit cannot be made directly because it would create a material conflict. This is why bimetallic lugs are used effectively in this capacity to bridge these dissimilar metals to allow the electrical system to function, while not making any material conflict in the scheme. The electrical system components must all be compatible, particularly under the applications of continuous load, or applicable to variable environmental conditions.
During system upgrades or retrofitting
On many older electrical installations, copper conductors were used throughout the entire installation. In the case of electrical upgrades or expansions, aluminium conductors may be chosen because of cost, leading to an incompatibility with existing copper conductors.
Bimetal cable lugs are typically used to ensure a safe and functional interface between the old and new components in the overall system. This is especially important for retrofit projects where full rewiring of the system was not feasible or worthwhile, where select components are replaced instead.
Utility & infrastructure projects
In large-scale infrastructure projects like substations, transmission towers, and rail electrification, aluminium conductors are often employed due to the sheer size and weight of the cabling that is required. The electrical systems in these projects often terminate at copper-based equipment and require a method of transition that can sustain high loads with a range of environmental stresses.
In these high-demand environments, bimetal lugs, made as a mix between copper and aluminium lugs, are a common solution for interfacing between field-run aluminium cables and copper terminals on equipment, maintaining operational efficiency and effective lifespan.
Marine, Oil & Gas, and Mining Applications
Marine, oil & gas, and mining are specialised industries that often consider the reality that electrical systems operate in challenging environments subject to moisture, chemical vapours, and extreme temperatures. These industries use aluminium conductors in some parts of the electrical system in order to lessen the weight or installation costs.
Due to the corrosive environment and a desire for long-term performance, the use of bimetallic lugs becomes paramount when transitioning from aluminium wiring to copper-based control or distribution devices.
Final thoughts
Bimetallic lugs are critical when connecting aluminium conductors to copper terminals or busbars. They resolve the metallurgical challenge of dissimilar metal combinations, as well as providing a safe, stable electrical transition across any materials with mismatched electrical and mechanical properties.
Bimetal lugs must be used to ensure compatibility between conductors and termination equipment, especially where cost, weight, and/or legacy context apply; working in solar power, an industrial facility, in large utility systems, or with system upgrades, bimetallic lugs make sure electrical systems will perform safely and reliably, even if its established that the metals do not like each other.
In conclusion, you should always use bimetal cable lugs whenever terminating an aluminium cable onto a copper terminal. Chetna Engineering offers bimetallic lugs of exceptional quality that ensure you do it right from an engineering and safety perspective.