Aluminum as a conductor material: a lighter and more economical alternative

2021-11-11 08:53:52 By : Ms. Teresa Sun

Choosing conductive metals for different industries and applications can be a challenge. Copper is often used in cables and wires due to its excellent conductivity and ductility. But compared to aluminum, it is relatively heavy and expensive. In many cases, switching to aluminum, which is lighter and less expensive than copper, is a viable option. The successful use of aluminum is a matter of understanding the capabilities of this conductive metal and how to deal with the challenges it poses. The price of copper is US$4,323 per ton, which is currently more than twice that of aluminum, and the price of aluminum is US$2,043 per ton (as of February 2, 2015). Compared with copper, the availability of the raw material aluminum is higher, which is a significant difference in price. After oxygen and silicon, aluminum is the third most common element in the earth's crust, and copper ranks 25th in availability on the list of raw materials. The volatility of the raw material market has further strengthened the assessment of current prices. If you look at the figures for the past five years (2010-2014), the price of copper fluctuated in the range of US$3,674 to US$5,980 per ton. In 2004, the average annual price was still US$1,895 per ton. This kind of fluctuation range does not exist in the aluminum industry, and material planning can be better. If aluminum is used as a conductor material, its lower conductivity requires a wire diameter that is about one-third larger than that of copper wire. However, in the end, the insulating material used with the wire plays a crucial role in performance, and the aluminum wire can have the same current-carrying capacity as the H07RN-F copper wire. The larger wire diameter of aluminum will only be disadvantageous in applications that require close spacing, such as when installed in a densely packed control box. When it comes to weight, the fact of aluminum speaks for itself. As a raw material, aluminum is about 70% lighter than copper. This contributes to the efforts of many applications that seek to reduce the weight of all components. Naturally, when used in cables, their lighter weight makes them easier to install. For a long time, high-voltage wires have been made of aluminum; the lighter weight significantly reduces the tension on the wires and masts. But even industries such as automobile manufacturing and the aviation industry are turning to aluminum wire. This is why the entire aluminum wiring harness has been installed on the Airbus A380. Aluminum wire is 60% lighter than similar current-carrying copper wire. Even for applications that require flexible cable connections, copper is no longer the first choice. HELUWIND® WK POWERLINE ALU series provides fine wiring solutions, including connection technology. The material properties of aluminum are very different from those of copper. These differences must be considered when handling cables and selecting connecting components.

When exposed to oxygen, the aluminum surface will form a hard and corrosion-resistant oxide coating in a short time. The coating protects the underlying material from further corrosion. This effect makes aluminum a highly durable material. However, when it comes to electrical engineering, a protective oxide coating on the surface of the material is not desirable. It reduces the conductivity of aluminum and makes contact difficult. If the oxidized conductor is connected without any pretreatment (removal of the coating), the contact resistance between the aluminum conductor and the connector assembly will increase. This will cause the temperature to rise, and in the worst case can cause the cable to catch fire. To prevent such problems, the oxide coating must be destroyed or physically removed. This can be done by brushing the bare aluminum conductor ends before contact and during the crimping process: aluminum conductor connector assemblies are factory equipped with special contact grease, usually a granular abrasive material such as corundum. Combined with high pressure, the corundum particles will have an abrasive effect, destroy the non-conductive oxide coating on the aluminum, and improve the contact performance and electrical connection. Grease also prevents moisture and oxygen from entering and causing new corrosion at the contact points. Better quality cable lugs are usually equipped with plastic plugs to prevent contact grease from drying out or leaking during storage.

The aluminum/copper hybrid cable lug has been fixed on the fine stranded aluminum conductor using C8 crimping.

Use C8 crimp for best contact

For the design of thin-wire conductors, we recommend IEC 61238-1 Cl. Due to the large oxidized surface of the conductor, use C8 crimping that has passed the A test. The C8 crimp profile is inserted very deeply into the stranded wire harness, tearing the individual strands evenly, so as to achieve the best contact of all strands, even in bundled conductors. Use C8 crimping (which has been developed as part of the POWERLINE aluminum series) to achieve the best electrical value (low contact resistance) and mechanical pull-out force.

Compatibility with electrochemical precious metals

When specifying electrical connection components, the corrosion reaction of aluminum in the presence of other metals (mainly copper) must also be considered. When aluminum comes into contact with more precious metals (metals with higher potential), such as copper, iron, or brass, electrochemical reactions may occur by forming contact elements. The reaction is activated by conductive liquid-mainly activated by condensed water (condensation) in the field. In this process, the potential difference generated by the electrochemical voltage sequence plays a vital role. The copper electrode (anode), electrolyte (water) and aluminum electrode (cathode) form a contact element. Any voltage on these components will be short-circuited by the contact between copper and aluminum. The resulting current produces a decomposition process in the aluminum, which is a visible radiant oxidation point, revealing the pollution of tiny copper particles. However, copper will not decompose. However, the decomposition process will have a long-term negative impact on the electrical connection, and as the contact resistance increases, it will lead to a rise in temperature and even fire. Therefore, we recommend using aluminum/copper (Al/Cu) cable lugs to connect aluminum to copper peripherals. Bimetal connectors, such as aluminum/copper cable lugs, crimp connectors, and connecting bolt pins, are manufactured using a friction welding process. They are encapsulated to prevent liquid from penetrating the connection and causing any unnecessary creepage. Using aluminum/copper connectors and connections is the most sensible way to combat the effects of oxidation on aluminum. Another way to prevent moisture is to install secondary insulation in the contact area. Depending on the application field, mechanical load and environmental conditions, cold shrink tubing, roll shrink tubing or heat shrink tubing can be used. The best protection effect is achieved by shrink tube with internal adhesive. At the same time, electrical contacts should be thoroughly inspected during regular maintenance.

Reduced connection strength due to creepage

Finally, the creepage characteristics of aluminum must be considered. Aluminum is a softer metal than copper and will expand or stretch over time, especially when subjected to higher pressures and temperatures. Classic crimp connections that are affected by leakage will lose strength and are no longer reliable to ensure proper connection. HELUKABEL's C8 crimp has a filling degree of 95%, which cannot be achieved by traditional crimp connections. The described expansion/stretching process is compensated by excellent extraction values. At the same time, we recommend regular maintenance and inspection of all clamping points according to the load level.

Aluminum wire was used instead of copper wire in the 1970s. One of the schools we worked with often had fires, which would consume the entire ventilator. This was traced back to the aluminum wire, and all fires started from the connection of the equipment. The building was constructed and inspected in accordance with applicable state and national wiring codes. This article helps to understand why this happens. If it is built correctly, it must still be inspected regularly. We use a thermal infrared scanner that is bulky and uses nitrogen. From a maintenance point of view, both copper and aluminum wires must be thermally inspected, but the risk of aluminum wires seems to be greater. Is this assumption correct? We noticed that the extension of the aluminum wire requires regular re-tightening of all connectors. We usually do not use copper wire for this operation on a regular basis.

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