Connecting aluminum wire to copper, while a simple process, involves safety considerations due to the distinct properties of these two metals. Aluminum wire and copper wire differ in their electrical conductivity, thermal expansion, and reactivity, which can lead to serious safety hazards if connections are not made properly. The direct connection of aluminum wire to copper without the correct measures can lead to galvanic corrosion and increased electrical resistance, potentially resulting in overheating, system failure, or electrical fires.
Understanding these risks and the correct methods to mitigate them is important for maintaining the safety of your electrical infrastructure.
Aluminum Wire vs Copper Wire
Before discussing anything else, it is important to understand the basic properties of aluminum wire vs copper wire, and the challenges that arise when these metals are connected in electrical systems.
The 4 principles below outline the reasons why special methods must be used in order to safely connect aluminum and copper wire:
Conductivity of Aluminum Wire vs Copper Wire
Copper:
Of all metals, copper is among the best conductors of electricity, second only to silver. The conductivity of copper is about 59.6 million Siemens per meter (Siemens/m) at 20°C.
Its low resistivity (approximately 1.68 microohm-centimeters at 20°C) makes it highly efficient for carrying electrical current with minimal voltage drop & heat generation.
Aluminum:
Aluminum’s conductivity is approximately 61% that of copper, with about 37.7 million Siemens per meter at 20°C.
Aluminum has higher resistivity than copper, about 2.82 microohm-centimeters at 20°C, meaning it has higher resistance and less efficiency in conducting electricity compared to copper.
This means that if an Aluminum wire and Copper wire of the same size are used with the same electrical load, the aluminum wire will generate more heat. This heat leads to thermal expansion of the wire, which we discuss below.
Thermal Expansion of Aluminum Wire vs Copper Wire
Copper:
Copper has a coefficient of thermal expansion of approximately 16.5 x 10^-6 per degree Celsius. This property indicates how much the length of the material changes with temperature.
In practical terms, this moderate rate of expansion affects how copper wiring behaves when heated, which can potentially loosen connections over time if not properly accounted for. But is not typically of great concern.
Aluminum:
Aluminum’s coefficient of thermal expansion is about 23.1 x 10^-6 per degree Celsius, which is significantly higher than that of copper.
This higher rate of thermal expansion means that aluminum will move significantly when heated. This can lead to a greater degree of mechanical stress at connections in response to temperature changes, increasing the risk of connection failures.
Oxidation of Aluminum wire vs Copper Wire
Copper:
While copper does oxidize over time, forming a green patina (copper carbonate) when exposed to air, it does so much more slowly than aluminum. While this oxidation layer is protective against further corrosion, it is not conductive and can impair electrical connections.
In environments where copper is exposed to sulfur compounds, it can undergo rapid corrosion, leading to formation of copper sulfide which also hinders electrical conductivity.
Aluminum:
Aluminum oxidizes rapidly in the presence of oxygen to form aluminum oxide, a very hard, protective layer that is highly resistant to further corrosion.
The aluminum oxide layer forms almost instantly when aluminum is exposed to air. Although highly protective, this oxide layer is non-conductive and impairs electrical connections, as it must be penetrated or removed to ensure a good conductive path.
Galvanic Corrosion
The combination of aluminum and copper in electrical connections introduces a risk of galvanic corrosion. This occurs because when two dissimilar metals are in contact, especially in the presence of an electrolyte (which can be as common as moisture in the air), the more reactive metal (in this case, aluminum) corrodes faster than it would have on its own. This corrosion leads to increased resistance at the joint and the buildup of heat, which will lead to damage and potential fire if unchecked.
In the case of connecting aluminum wire to copper, galvanic corrosion is managed by a pair of different methods which are discussed below.
Methods of Connecting Aluminum Wire to Copper Wire
To mitigate the risks associated with direct metal-to-metal contact between aluminum and copper, various approved methods and specialized connectors have been developed. These solutions are designed to ensure stable, long-lasting connections that minimize the potential for corrosion and overheating. Here is a look at the most effective techniques:
Specialized Wire Connectors
CSA-Approved Wire Connectors: It is crucial to use connectors that are specifically designed and CSA-listed for aluminum-to-copper wire connections. Products like AlumiConn Connectors are a popular choice because they feature separate ports for aluminum and copper wires, eliminating the risk of direct metal contact and providing a secure mechanical connection.
Crimp Sleeves and Connectors
Mechanical Crimps: Another effective method involves using crimping tools with special aluminum-to-copper crimp sleeves. There are several different brands and methods of this, with Copalum Crimps being a popular choice. These crimp sleeves are designed to hold the wires securely together without requiring twisting or soldering.
Antioxidant Compounds
Application of Antioxidant Paste: Before making a connection, applying an antioxidant compound such as Noalox to the aluminum wire can significantly reduce oxidation at the connection point. This paste inhibits corrosion of the metal and helps to ensure a safe, low resistance electrical path.
The antioxidant compound should be applied liberally over the stripped part of the aluminum wire and inside the connector before the wires are inserted. This ensures that the entire surface susceptible to oxidation is protected.
Making Safe Connections of Aluminum Wire to Copper Wire
It is important that best practices are followed when connecting aluminum wire to copper wire to ensure a safe, low resistance electrical connection. The following is a step-by-step guide to doing the job properly.
Preparation
Strip the Wires: Begin by stripping the insulation from the ends of both the aluminum and copper wires, exposing enough metal to ensure a secure connection within the connector. Typically, about ¾ inch of bare wire is needed, more if the wires being used are of a larger gauge. Ensure the amount stripped is enough to push bare metal all the way into or through the connecting lug being used, with little to no wire visible at the point of entry.
Clean the Wires: Using a wire brush or special cleaning tool, gently clean the aluminum wire to remove any existing oxidation. This step is crucial as aluminum oxidizes quickly when exposed to air.
Application of Antioxidant Compound
Apply Antioxidant Compound: Generously apply antioxidant compound to the stripped portion of the aluminum wire. Ensure the compound covers all exposed metal, as this will help prevent future oxidation and ensure good electrical conductivity.
Insert the Wires into the Connector: Carefully insert the prepared aluminum wire into its designated port in the connector. Follow by inserting the copper wire into its respective port.
Installation of Connectors
Secure the Connection: For screw-type connectors like AlumiConn, tighten the screws firmly to the manufacturer’s recommended torque. This prevents any movement that could lead to wear or poor contact.
Crimp Connectors: If using crimp connectors, position the crimp sleeve over the wire junction and use the appropriate crimping tool to apply pressure. Ensure the crimp is tight and secure, providing a stable mechanical connection that will not easily loosen.
Final Inspection: Double-check each connection to ensure it is tight and secure. There should be no movement at the wire junction, and all metal should be adequately covered by antioxidant compound. Wiggle the wires back and forth repeatedly where they enter the connector and re-tighten if necessary.
These wires have been properly stripped and entered into this connector.
Testing the Connection
Conductivity Test: Once connections are made, it is advisable to test the circuit for proper conductivity and to ensure there are no short circuits. Use a multimeter to test continuity and resistance across the connection.
Visual Inspection: Regularly inspect the connections for any signs of corrosion, overheating, or loose fittings, especially during the initial period after installation.
Maintaining the Connection
Scheduled Inspections: Set a schedule to periodically check the connections, especially in environments that may accelerate corrosion (e.g., high humidity areas). Inspections should include a physical check and a test for electrical integrity.
Reapply Antioxidant Compound: During inspections, consider reapplying antioxidant compound if any drying or wear is observed.
By following these detailed steps, you can create safe and reliable electrical connections between aluminum and copper wires, minimizing the risk of electrical failures and ensuring compliance with safety standards. This proactive approach to installation and maintenance will contribute to the long-term safety of your electrical system.
While there is nothing wrong with performing electrical work DIY, you should contact a professional should you have any concerns regarding the safety of your electrical project. Celtex Electric & Automation are your local Calgary electrical specialists, with extensive experience in making aluminum to copper wire connections, aluminum remediation and more. Call our team for an obligation free consultation today.