What is the difference between Aluminum and copper in electrical applications?
One must take into account the differences in material properties, such as capacity, weight, and cost between Aluminum (Al) and copper (Cu) for an electrical application.
Aluminum (Al) was more common in the past for products such as bus bars, fuses, and circuit breakers. However, lately, some designers have changed components from Al to Cu (Copper). Today, due to cost stability and coating, some designers are going back to using Aluminum.
Misconceptions may arise about Al and Cu’s properties due to the different grades of metals used in various electrical applications. Cu (Copper) used in electrical cables and equipment is nominally pure.
Pure Aluminum, however, is often not strong enough for electrical applications. Also, keep in mind that different alloys have changed over time due to evolving applications.
The different alloy properties of Aluminum are also changing, depending on the processing. For example, Al 6101 is stronger than Al 1350. However, the Al6101 heat treatment hardens it and improves its strength. Different metal grades, such as Al 6101 and Al 1350, will vary in comparison with Cu. During the design process, it is essential to have the properties of the specific material used.
Properties of Copper and Aluminum
Weight, electrical capacity, and cost are important considerations when selecting Al or Cu for an electrical application. However, other factors are also important; for example, the resistance in electrical connectors can increase or decrease and expand a material.
When a connection is thermally cycled, expansion can increase the clamping force, deform contact points, and promote creep in materials. This will be a significant concern with Aluminum because its coefficient of thermal expansion, depending on the alloy, is approximately 42% greater than Cu, but Al can dissipate heat more quickly.
Taking advantage of the lower modulus of elasticity since the 1990s, extruded aluminum bus bars have increased surface area, keeping temperatures down. When designing in any of the materials, the connections must be robust to avoid poor connectivity over time due to deformation from thermal expansion and creep.
A common mistake is to consider that Aluminum is soft, and compression connectors should be used. However, with some design and plating changes, mechanical pressure connectors and compression connectors are no longer required. In some cases, alloys or processing are used to make Aluminum equal to Cu.
Aluminum may require a coating to reduce oxidation as this can affect the connection, even an Al to Al connection. Also, the coating often includes tin or silver. These materials reduce corrosion on Aluminum and Cu, as they are prone to oxidation when exposed to the atmosphere.
Corrosion is also a problem when there are two different metals in a system. Aluminum will react electrochemically with Cu if moisture (moisture that would act as an electrolyte) is introduced. Al to Cu cable clamps are connectors that have been friction-welded and encapsulated to prevent corrosion from damaging an Al to Cu connection.
Proper connections are essential, as corrosive wear is also a concern. Al and Cu are compatible metals, so contact can create a bond that can promote wear. Although corrosive wear is more of a problem for moving parts, a technician may need more time in the field if the wires get stuck to the busbar.
Weight and electrical capacity of copper and Aluminum.
Possibly, the main property of the material to decide between using Al or Cu in an electrical application is its conductivity.
Copper (Cu) offers a better electrical capacity by volume. However, Aluminum has a better capacity by weight. According to Uwe Schenk, global segment manager of Helukabel, “as a raw material, Al is approximately 70% lighter than Cu. For cables, Aluminum can be up to 60% more lightweight than cable with comparable copper current capacity “.
The weight is not a direct ratio as more Aluminum (Al) is needed to match the Cu capacity. Al carries approximately half of the Cu capacity (56% in Al6101). The difference in the weight/electrical capacity ratio means, in general, that one pound of Aluminum has an electrical conductivity equal to 1.85 pounds of Cu.
For example, a Cu busbar could weigh about 550 lbs. The same busbar in Aluminum would be about 300 lbs. Reducing the weight can help with shipping or even labor costs.
Other Considerations when comparing Aluminum and copper (Al vs. Cu)
Although installation and handling work is not a property of the material, it does affect the cost. Some projects may be more cost-effective if weight can be reduced, whether this translates into shipping, installation, or other expenses.
However, this may not be better in all applications. Consider the added diameter in an Aluminum cable to match the Copper (Cu) capacity. The National Electrical Code (NEC) gives rules about how much wire is allowed to fill a conduit.
There are more rules than this, but in general, when there are three or more wires, the pipe’s filling should be 40% or less. However, NEC Section 501 says that only 25% fill or less is acceptable if the conduit is in hazardous locations. This means that increasing the aluminum size may increase the labor cost for the additional or larger conduit that now needs to be run to meet the NEC.
For a general example, if the 14 AWG wire is changed from Cu to Al, the wire size is increased to 12 AWG, which will reduce the maximum amount of wires allowed in a conduit from ¼ inch (maximum fill: Cu = six wires, Al = three wires at 40% fill).
If this application requires four wires, you can reduce the fill by using two pieces of conduit or a larger size, which will use more energy for bending, materials, and installation. Any of these solutions could increase the labor and materials in the installation.
There have been other problems with Aluminum in electrical components. Historically, Aluminum was often used in switches (fuses and circuit breakers).
Unfortunately, in the past, welding was often necessary to hold the switches. Field soldered Aluminum may have been what prompted designers to switch to copper (Cu). Since this time, they have offered busbars with dovetail holes or slots that allow for easier installation and do not necessarily have to be soldered.
Despite addressing these processes, manufacturers like GE reported that many customers began ordering Cu bus bars instead of Aluminum (Al). Manufacturers will produce in the order of the designers, so the Cu was produced in greater volume. Some of the past problems with Aluminum, although corrected, gave a boost to Cu manufacturing.
Despite this trend, cost and planning remain vital factors when estimating projects. Aluminum is the third most abundant material in the earth’s crust, while Cu is the 26th. This has fluctuating Cu prices while the cost of Aluminum is more stable.