Connection of copper and aluminum conductors

About the connection of copper and aluminum wire goes a lot of rumors. Some say that there is nothing terrible in this, and they give examples when such compounds have served for decades, while others say that they know from practice how quickly they are destroyed. Who to believe and how to connect such wires correctly will be discussed in our article.

Why can not connect copper and aluminum wire

First of all, let's see why you can not connect these wires together, and what is needed for such a connection to serve for many years. To do this, we will have to immerse a little in theory and understand the structure of these metals.

Why can not connect copper and aluminum wire

To understand how to connect copper and aluminum wire, let's see what is in such a connection. After all, there are several theories about the inadmissibility of such a connection, and almost all of them have a rational grain.

Aluminum oxidation

Like any other metal, under the influence of oxygen, copper and aluminum are oxidized. As a result, an oxide film is formed on their surface. The oxide film of copper practically does not prevent the passage of electric current, but the oxide film of aluminum has a rather large resistance.

If we connect the copper and aluminum wires, then no matter how much we want, the metals will interact. Aluminum is a more active metal, therefore, when moisture appears between the compound, which is in any case present in the air, the electrolysis process begins, that is, aluminum ions are transferred to copper.

As a result, the aluminum conductor loses its mass. It forms voids and shells. They, in turn, also oxidize and accelerate the electrolysis process even more. And the more moisture in the compound, the faster this process occurs.

What is electrolysis?

As a result, we have almost destroyed aluminum conductor. Its cross section is reduced, which means the current density increases. The current density increases, the metal begins to heat up more, and as a result, it will lead either to aluminum burning out at the junction, or, in the worst case, to a fire.

How to connect copper and aluminum conductor

But copper wire can be connected with aluminum. To do this, it is sufficient to place a third material between these two conductors or completely eliminate the possibility of moisture penetrating to the place of contact of metals.

• Let's look at both of these options. Let's start with the simplest - to place a third metal between conductors. Usually, an inactive metal is also chosen for this, so that we again do not have an electrolysis process. And usually the instruction recommends using brass for this.

The connection of copper conductor and aluminum through a steel washer

In the photo the same connection after heating the washer

• This is due to the fact that this material has fairly good electrical properties. It is chemically resistant and interferes with the electrolysis process.
• Some suggest using regular steel or stainless steel. But this is not worth doing. The fact is that these materials have not very good conductivity. Therefore, when large currents pass through them, they will be very hot. As a result, we can again get a fire.

Brass washers

Note! If you still decide to stop at the bolted connection, then instead of a steel washer, you can use brass. If you have metal, you can cut it yourself. The variant with a steel washer is permissible to use only in networks with a not very large load.

• The second possible option is to exclude the ingress of water into the place of the connection of metals. Sealing the connection would be too expensive, and not always a reliable option. Therefore, in most cases, for this purpose, a special paste is used as in the video.

Contact grease

• Such a paste not only prevents moisture from entering the contact compound, but also oxygen. As a result, aluminum is oxidized very slightly, because for the formation of an oxide film it needs just a few seconds. And due to the absence of moisture at the junction, the most terrible process for such a compound does not occur - electrolysis.

How to connect copper and aluminum wires correctly

Knowing the causes and possible solutions to the problem, you can proceed to the analysis of the question of how to correctly connect the copper and aluminum wires. And here there are several quite logical answers, some of which we have already given in the section above.

Let's start with the question of lubrication. It can be technical petrolatum, lithol and any other lubricant that prevents metal oxidation and moisture ingress. But then the question arises with the subsequent isolation of such a connection. After all, the tape lies very poorly on the lubricant, and the heat shrinking can simply squeeze it out.

Note! In any case, twisting type connection is prohibited. And for such different metals, twisting can be doubly destructive.

Wire Terminals

Connect copper and aluminum wire using a variety of terminals. It can be spring, screw or any other types, but it should be borne in mind that aluminum and copper should not touch.

Brass Wire Lugs

If you are trying to connect single-core aluminum and stranded copper wire with a screw terminal, then it is advisable to use special brass tips. And they should be used for both metals.

Crimp terminals for screw connection

This is due to the fact that with a screw clamp aluminum, it can lose partially or even completely its cross section. Aluminum material is quite soft and high-quality twisted screw can fully transfer it.

The tip on the copper stranded wire

With stranded copper wires a similar situation. But only in this case, when tightening the screw, it can break a part of the wires in the conductor. Again - the reduction of the cross section. Therefore, these tips can be an excellent panacea for such accidents. Moreover, the price of such products is mere pennies.

Crimping sleeves

One of the possible options for how to connect the copper wire with aluminum, could be the use of special crimping sleeves. Now the market is widely represented sleeves made of brass. For a clearer demonstration, one of their edges is white and the other color is copper. They are specifically designed for crimping copper and aluminum wires.

Solder wire connection

Aluminum and copper wire can be connected by soldering. Only in this case, you need a special solder for aluminum and high-quality tinning of copper conductor. By the way, already one tinning of copper conductor will be enough to prevent electrolysis.

Welding wires

Welding for such compounds is usually not used due to the different melting points of metals. And it does not protect against the process of electrolysis. Therefore, it is better to forget about welding wires.

Tips for screw connection for wires of large cross section

Before connecting aluminum and copper wires of large cross-section, it is better to put special tips on them. They are dressed by pressing and usually have a brass contact part. This allows them to be further connected with a conventional screw connection without any problems.

Conclusion

When asked how best to connect copper and aluminum wire, there is no definite answer. After all, it all depends on local conditions and accessories available at hand. But in any case there are a lot of such options. Only direct stranding of them is not allowed, which is in any case prohibited by the rules of OLC.