How To Connect Copper and Aluminum Wire (The Correct Way)

Aluminum and copper are both commonly used materials for wiring and cables. Most electronic cables are made using copper, but it’s expensive. Aluminum wires have about 40% less carrying capacity than copper, so you’ll need more of it to do the same job as a copper wire. But the aluminum wire is cheaper and lighter, so it’s good for many applications. 

You can connect copper and aluminum wire together, but you’ll have to use the correct equipment to do it safely. Connect the wires using a splice connector or nut clamp rated for an AL/CU connection. Using pigtails or approved connectors will reduce the risk of problems and fire hazards. 

Before you dive into your next home improvement project, it’s important to understand how these two conductors work and how to use them both safely. This article will explain everything you need to know about copper and aluminum wires and share tips to connect them together. You’ll also learn about when not to connect copper to aluminum.  

The Differences Between Copper and Aluminum Wire

While copper and aluminum are both commonly used for electrical wiring, they have different properties and capabilities. The biggest difference between the two is that copper is more stable than aluminum. Aluminum is more susceptible to temperature fluctuations and oxidation than copper, especially over long periods of time. 

1. Copper Has Higher Conductivity

Compared to aluminum, copper wire has much higher conductivity. In fact, aluminum has about 40% less conductivity than copper. That means that electrical currents run much easier through copper wiring than aluminum. That means copper wires can be smaller to run the same amount of current, and the wires can withstand more electrical power running through them. 

What is thermal conductivity

The conductivity is because copper has lower resistivity than aluminum. That means the current can run through the wire with less resistance. The connection is better, more stable, and produces less heat to disperse. 

2. Aluminum Wires are Lighter

Aluminum is a very light metal, so wires made from aluminum are much lighter than copper wires. That means that aluminum is typically cheaper to use, but you’ll also need more wire to do the same job. In some applications, a heavier wire may be more appropriate. However, in other applications like in overhead power lines or aircraft, lightweight aluminum wires may be more suitable. 

3. Copper Wires Resist Thermal Effects

Electricity generates heat, which causes components (like wiring) to expand and contract with temperature changes. Copper has a lower coefficient of thermal expansion than aluminum. That means that copper is less likely to change in volume as the temperature increases or decreases. 

Over time, the expansions and contractions from temperature fluctuations can cause damage, especially at joints and junctions. At connection points, thermal effects can cause wires to come loose or have a bad connection, causing arcing. When electricity arcs off the wire, it could cause a fire or electrocution if it’s around an outlet or power switch. Using copper wires helps prevent those issues. 

4. Aluminum Wires are Corrosive 

Over time, metal surfaces tend to show the effects of their exposure to oxygen and other elements. Copper wire oxidizes and turns green, but the coloration doesn’t impact the connectivity of the wire. Copper is resistant to most organic chemicals, meaning it can resist corrosion and breakdown over time. 

Aluminum, on the other hand, begins to corrode over time and can develop a crusty buildup on the outside of the wire. That corrosion can impact the wire’s connectivity and cause it to malfunction over time. Corrosion can also cause a gap in the wire connections, which could lead to dangerous arcing. 

Tips for Connecting Copper and Aluminum Wire Together

If you have one type of wire already installed in your home and are looking to connect the other type of wire, you can safely connect them if you do it the right way. You must take the differences between aluminum and copper into consideration when connecting them together. Here are some tips to ensure you do the job correctly and safely. 

1. Only Use AL/CU Rated Connectors

Connectors are rated for their use, so you’ll know what kind to use for your project. When you connect copper and aluminum wires together, you’ll need to account for the risk of corrosion (aluminum) and the differences in resistance, thermal effects, and so on. 

The National Electrical Code (NEC) specifies that when you connect copper and aluminum wiring, you must use a specially-rated connection device. These will be marked as AL/CU rated. Using the correct connector will ensure a safe and secure connection between the two wires and reduce the risk of fire or injury. 

2. Use the Correct Connector Size

When you choose a connector, it needs to be the appropriate size to securely fasten the wires together and create a good connection. If you use a connector that’s too big or too small, the connection may not be secure, which could create an arc hazard. A weak connection is always a potential danger. 

For example, a connector that’s too big may allow the wire to wiggle around inside, or it may slip out. This would cause a live (hot) wire to potentially make contact with a surrounding surface. This could cause a fire, shock, electrocution, or damage to surrounding wiring. 

3. Use Corrosion Inhibitor Paste

Since the aluminum wire is much more susceptible to corrosion than copper, you’ll need to protect it against those effects. Corrosion inhibitors work as a protective coating to keep moisture, oxidation, and other environmental factors from affecting the wire. 

Since corrosion isn’t a concern with copper wire, you may not know how the area will affect aluminum wire. So, it’s best to apply the protective barrier to keep the aluminum in good condition for years to come. That way, oxygen won’t cause a corrosive buildup to develop on the wire, which could impact the connection and cause damage. 

4. Ensure Wires Are Secure

Having a good connection between wires is critical to keeping the electrical current contained. When connections become loose, there’s a risk of causing a short or dangerous power arc that could result in a fire or worse. 

When you’re connecting copper and aluminum wires, you’ll need to be sure your AL/CU-rated connector is fitted properly on the wires, and the connection is tight and secure. Check that the wires don’t easily pull out or shift around.   

Why Should I Not Connect Copper and Aluminum Wires? 

While it’s generally okay to connect copper and aluminum wires (as long as you do so using an approved connection device), there are some situations where you shouldn’t do so. 

When aluminum and copper wires are spliced together, it’s critical that the correct devices are used. Improperly connecting the two is a huge fire hazard and causes a big chunk of the house fires that happen each year. 

Since aluminum is already susceptible to oxidation and corrosion, the problem becomes even more serious when it’s connected directly with copper. Over time, the differences between the two metals can cause the connection or splice to become loose. The two metals expand and contract differently at different rates and react differently to electrical currents. Once the connection becomes loose, there’s a risk of an arc, overheating, and electrical fires. 

So, if you’re splicing the wires in a location that’s already susceptible to temperature fluctuations and excessive vibrations or jostling, you may not want to add to the risk by connecting aluminum and copper together. 

How to Connect Copper and Aluminum Wires Correctly? 

If you’re ready to go ahead with your project and need to connect copper and aluminum wires together, it’s important to do it properly. Incorrectly connecting these two conductors can lead to fire hazards or injuries. 

You should start by purchasing an approved AL/CU connector that complies with NEC Section 110.14. The connectors must be rated as AL/CU and have a genuine UL symbol.

Some examples include: 

  • Ideal Twister Connectors
  • King Innovation 2-port or 3-port connector lugs
  • King Innovation AlumiConn copper lugs
  • Quick splice connectors

Next, shut off the power at your circuit breaker and verify that no current is running to the wires you’re going to work on by using a voltage detector. 

Do a visual inspection of the wires. If they appear burnt, damaged, or heavily corroded, the wires and circuitry should be replaced, and you may need to call a professional to do the work. 

Next, apply corrosion inhibitor gel to the wires to prevent future corrosion, as we discussed earlier. 

Expose the wire by stripping away the insulation jacket so that you have at least ½” to one inch of wiring to work with. If you’re using an Ideal twister, use pliers to twist the copper and aluminum wires together, so they’re tight and secure. You don’t want to leave any gaps, so don’t try to twist it with your fingers. 

If you’re using a connector lug, insert the wire into the appropriate port and tighten the lug with a flathead screwdriver. Follow the manufacturer’s instructions for installation. 

When you’re done, give the wires a gentle tug or wiggle them around to make sure they’re securely fitted into the connector device. This will ensure you have a good connection, and they won’t fall out or come loose later on. When the job is complete, you can turn the power back on at the breaker to finish the work. 

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