Why can't copper and aluminum wires be joined together? Why it is impossible to connect aluminum and copper wire by twisting The mechanism of interaction between two metals.

In order for the power supply in your homes to always be of high quality, uninterrupted and reliable, it is very important when installation work connect the wires correctly. There are a lot of ways, we will consider each one in detail with its advantages and disadvantages, with step by step instructions performing switching. We will also pay attention to the eternal question of electricians - how to connect wires whose cores are made of different metals (for example, copper and aluminum).

Removing the insulating layer from the wires

Immediately I would like to dwell on a question that will be common to any method. Before connecting the wires into a common electrical unit, they must be stripped from the upper insulating layer.

This can be done with a utility knife. This method is simple, but there is a high probability of damage to the conductive core. To do everything right, you must clearly follow the step-by-step instructions:

1. Place the wire on some flat surface (like a table).
2. Press it with the index finger of your left hand.
3. Take the knife with your right hand and lightly press it into the insulating sheath of the wire. In order not to hook the metal core, position it towards the cut at an angle. If the angle is right, there is a possibility of a circular notch in the core, as a result of which it may subsequently break.
4. Holding the knife in this position. index finger with your left hand, slowly rotate the conductor one full turn thus cutting the insulation all around.
5. It remains only to pull off the cut piece of insulation.

Professional electricians now already have in their arsenal such a device as a stripper. This is a multifunctional tool, with it you can strip the insulation from the wire or cut the cable. It can be simple, semi-automatic and automatic. Most importantly, when stripping the insulation with a stripper, the conductive core is not damaged. For each standard core diameter, such a tool has a calibrated hole with a cutting edge.

The length to which it is necessary to strip the wire cores is different for each connection method.

Twisting

Let's start with the simplest and most well-known method - twisting. It can also be called the oldest, not for nothing that electricians among themselves call twisting the “grandfather method”.

We will not tell you that such a wire connection is durable and reliable. According to the main document in electrical engineering, PUE (“Rules for Electrical Installations”), twisting is generally prohibited, despite the fact that half a century ago it was used everywhere. The fact is that in those days, the load in the apartments consisted only of lighting, radio or TV. Considering the current load in modern apartments with a huge amount of household appliances used daily, then no old insulation, core cross-sections and wire connection methods are no longer suitable.

Nevertheless, we will talk about twisting, and even in the first place, because it is the main stage in such connection options as welding and soldering.

Positive sides

The most important advantage of twisting is that it requires absolutely no material costs. All you need is a knife to remove the insulating layer from the wire strands and pliers to make the connection.

The second indisputable advantage of twisting is ease of execution. No special knowledge or skills are needed, anyone who has ever held pliers in their hands can do it.

In a twist, several wires can be connected at the same time, but their total number should not exceed six.

Negative sides

The main disadvantage of twisting is its unreliability, it weakens over time. This is due to the fact that there is a residual elastic deformation in the cores of the cable or wire. In the place of twisting, the transition resistance increases, which is fraught with a breakdown in contact and heating. In the best case, you will find it in time and re-seal the junction, in the worst case, a fire may occur.

Using twisting, it is impossible to connect electrical wires made of different metals. As an exception, you can twist copper and aluminum wire, but only if the copper core is pre-tinned with solder.

In electrical engineering, there are concepts of a detachable or one-piece connection. So twisting does not apply to either one or the other. A detachable connection is characterized by the fact that its ends can be separated many times. In twisting, this cannot be fully done, each time after the next promotion and twisting of the cores, they will deteriorate. It is also impossible to call twisting an integral connection, because it does not have the concepts of strength, reliability and stability necessary for this. This is another disadvantage of the twisted connection.

Mounting

If for some reason you do not have the opportunity to use other methods of connecting electrical wires, you can use twisting, just do it with high quality. Very often it is used as a temporary option and is subsequently replaced by more reliable switching methods.

How to connect wires with a twist? To begin with, the veins are cleaned by 70-80 mm. The main thing is to twist all switched conductors into one single twist at the same time, and not wind one around the other.

Many mistakenly begin to twist the cores together from the place where the insulating layer ends. But it is better to clamp both wires in this place with one pair of pliers, and with the second, grab the ends of the wires and perform rotational movements in a clockwise direction.

If the wire section is small, you can twist it by hand. Align the conductors with the insulation shear and hold them firmly in this place with your left hand. Bend all switched tips into one single bend at an angle of 90 degrees (a bend length of 10-15 mm will be enough). Hold this fold with your right hand and rotate it clockwise. This must be done firmly and firmly. If it is already difficult to twist with your hands at the end, use the pliers, as described above. As soon as the twist becomes even and beautiful, you can cut the bend.

You can also connect several wires in this way, but then, to make it easier to twist them, make the bend longer, somewhere around 20-30 mm.

How to properly twist the wires is shown in this video:

There is also a way to twist wires with a screwdriver, see about it here:

For twisting wires with a special tool, see here:

Now the resulting twist must be carefully insulated. For this, electrical tape is used. Do not spare it, wind it in several layers, and isolate not only the connection itself, but also step 2-3 cm over the core insulation. Thus, you will ensure the insulating reliability of the twist and protect the contact connection from moisture.

You can also insulate the connection of wires with the help of thermotubes. The main thing is not to forget to put the tube on one of the wires to be connected in advance, and then put it on the place of the twist. Under heat, the thermal pipe shrinks, so slightly heat its edges, and it will firmly wrap around the wire, thereby providing reliable insulation.

If the twisting is done with high quality, it is likely that it will serve you for many years, provided that the load current in the network is normal. But still, it is better not to stop at this stage and strengthen the junction by welding or soldering.

Soldering

Soldering is when electrical wires are connected using molten solder. This type of connection is most suitable for copper wires. Although there are now various fluxes for aluminum, experienced electricians prefer to refrain from such soldering. But if necessary, you can use special fluxes and even solder copper with aluminum.

Positive sides

This type of connection with twisting can no longer be compared, soldering is much more reliable (in terms of reliability, it is second only to welding).

With the help of soldering, it is possible to connect stranded and solid wires, as well as conductors of various sections.

This type of connection does not require any maintenance during the entire period of operation.

Soldering is considered low in cost, only a soldering iron is needed from the fixtures, and flux and solder are quite inexpensive, and their consumption is very meager.

Negative sides

The disadvantages of this method include high labor intensity. Soldering requires certain preparatory work, the cores of the wires must first be tinned before twisting. The surfaces to be soldered must be free from oxides and absolutely clean before starting work.

And of course, you need experience in owning a soldering iron, that is, the one who will connect the wires by soldering must have a certain qualification. Indeed, in the process of soldering, it is very important to maintain the required temperature conditions. An underheated soldering iron will not warm up the connection well; overheating is also unacceptable, because the flux will burn out very quickly, not having time to do its job.

Soldering is not a fast process, but this minus is compensated by the reliability that is obtained from the contact connection.

Mounting

The soldering process is as follows:

1. Remove the insulation from the cores by 40-50 mm.
2. Clean the exposed areas of the veins to a shine with sandpaper.
3. Dip a heated soldering iron into the rosin and run it over the cleaned surfaces several times.
4. Perform a twist.
5. Bring the tip of the soldering iron to the solder.
6. Now immediately heat the twist with solder, the tin should melt and fill the gaps between the turns.
7. Thus, the entire twist is enveloped in tin, after which it is allowed to cool.
8. Wipe hardened solder with alcohol and insulate.

Soldering wires with a soldering iron is shown in this video:

Soldering wires with a gas soldering iron:

Soldering twists by immersion in molten solder:

Welding

In order for the connection of electrical wires to be as reliable as possible, the considered method of twisting must be further fixed by welding. It is similar to soldering, only now a welding machine is used instead of a soldering iron.

Positive sides

This method is most preferable over all the others, as it meets all regulatory requirements in terms of reliability and quality.

The welding method is based on the contact heating of the ends of the wires with a carbon electrode until a ball (contact point) is formed. This ball is obtained as a single whole from the fused ends of all connected wires, which ensures safe and reliable contact, it will not weaken and oxidize over time.

Negative sides

The disadvantage of welding is that certain knowledge, experience, skills and special devices are needed to carry out such work, and you often have to turn to specialists.

Mounting

In order to connect wires by welding, you will need the following fixtures, tools and materials:

• welding inverter with a power of at least 1 kW, its output voltage must be up to 24 V;
• carbon or graphite electrode;
• glasses or a mask to protect the eyes;
• welding leather gloves for hand protection;
• fitter's knife or stripper for removing the insulating layer from the conductors;
• sandpaper (for cleaning the connected conductive surfaces);
• insulating tape for further insulation of the welding joint.

The sequence of work is as follows:

1. Free each connected wire from insulation by 60-70 mm.
2. Clean bare veins to a shine with sandpaper.
3. Twist, after biting off, the length of its tips should be at least 50 mm.
4. Fasten the ground clamps on top of the twist.
5. To ignite the arc, bring the electrode to the bottom of the twist and lightly touch the connected wires with it. Welding is very fast.
6. It turns out a contact ball, which is given time to cool, then insulate with tape.

As a result, an almost solid wire is obtained at the end, that is, the contact will have the lowest transition resistance.

If you connect copper wires in this way, then choose a carbon-copper electrode.

I would like to recommend that if you buy a welding machine (after all, it will come in handy not only for connecting wires, but also for many other purposes), then choose the inverter option. With small dimensions, weight and power consumption, it has a wide range of welding current adjustment and produces a stable welding arc. And this is very important to be able to regulate the welding current. If it is chosen correctly, the electrode will not stick, and the arc will hold steadily.

How welding is performed, see this video:

We examined the main types of wire connections. Now let's briefly talk about methods that are used less often, but also guarantee quality and reliability.

Crimping

For this method, special tubular sleeves or lugs are used, with which the wires to be connected are crimped and crimped. The essence of the method lies in the joint deformation of the sleeve and the cores inserted into it. During deformation, the sleeve is compressed and squeezes the conductive surfaces. The conductors are interlocked, which ensures the reliability of electrical contact.

The advantage of such a connection is reliability, as well as the fact that it can be classified as “done and forgot”, it does not need maintenance.

But along with positive aspects Pressurization also has a number of disadvantages. First, a special tool is required (crimper or mechanical or hydraulic pliers). Secondly, the quality of the connection directly depends on the correctly selected sleeve (it is selected depending on the number of connected cores and their cross section).

Before connecting two wires using crimping, they are not only stripped of insulation, but also lubricated with a special paste. Aluminum is treated with quartz-vaseline paste, it removes the oxide film and prevents it from reappearing. For copper conductors, quartz impurities are not needed, technical petroleum jelly is enough. It is needed to reduce friction. Also, lubrication minimizes the risk of damage to the cores during deformation.

Next, the cores must be inserted into the sleeve until they are mutually stop, and alternate crimping is performed on both sides. The crimped joint is insulated with insulating tape, varnished fabrics or thermotubes.

How to connect wires with sleeves is shown in these videos:

Bolted connection

Bolts for connecting wires used to be often used, now this method is more common in high voltage circuits. The contact is reliable, but the electrical assembly connected in this way turns out to be too cumbersome. Until recently, large junction boxes were installed in apartments, in them at least somehow, but it was possible to arrange such a connection. Modern boxes are smaller and are not designed for switching wires in this way.

But you definitely need to know about it, because this is one of the ways to solve the eternal problem of connecting conductors made of different metals. The bolt contact is ideal for switching absolutely incompatible conductors - thin and thick, aluminum and copper, solid and stranded.

The cores of the wires must be stripped and the ends twisted in the form of rings. A steel washer is put on the bolt, then the rings of the wires to be connected are thrown on (this is the case when they are made of homogeneous metal), then another steel washer follows and everything is tightened with a nut. If aluminum and copper wires are connected, one more additional washer must be placed between them.

The advantage of this connection is its simplicity. If necessary, the bolted structure can always be untwisted. If necessary, you can add more strands of wires (as far as the length of the bolt allows).

The most important thing in this type of connection is to prevent direct contact copper and aluminum, do not forget to lay an additional washer between them. And then such a switching unit will last a long time and reliably.

Modern technologies

In many cases, the methods discussed are gradually becoming a thing of the past. They were replaced by factory wire connectors, which greatly facilitated and accelerated installation and switching work:

1. Terminal blocks with tubular brass sleeves inside. Stripped wire strands are inserted into these tubes and fixed by tightening the screws.
2. PPE caps with compression springs inside. The cores are inserted into the cap and then it is turned clockwise with a little effort, thereby the connected wires are reliably squeezed inside.
3. Self-clamping terminals. It is enough to place the wiring in them, and there it is automatically fixed due to the pressure plate.
4. Lever-type terminal blocks. Such a connector reusable. It is enough just to raise the lever, insert the conductor into the contact hole and lower the lever back, reliable fixation is provided.

We do not talk in detail about all the existing terminal blocks, since there is a separate article about this, which discusses in detail each type of wire clamp.

We hope that we have clearly explained to you how to connect the wires correctly. Choose the method that suits you best. When choosing, take into account the cross section and material of the conductors, the location of the connection (outdoors or indoors), the amount of load current that will flow in this electrical circuit.

If you yourself are a scientist or just an inquisitive person, and you often watch or read the latest news in the field of science or technology. It is for you that we have created such a section, which covers the latest world news in the field of new scientific discoveries, achievements, as well as in the field of technology. Only the latest events and only trusted sources.

In our progressive time, science is moving at a fast pace, so it is not always possible to keep up with them. Some old dogmas are crumbling, some new ones are being put forward. Mankind does not stand still and should not stand still, and the engine of mankind is scientists, scientists. And at any moment a discovery can occur that can not only amaze the minds of the entire population of the globe, but also radically change our lives.

A special role in science is allocated to medicine, since a person, unfortunately, is not immortal, fragile and very vulnerable to all kinds of diseases. Many people know that in the Middle Ages people lived on average 30 years, and now 60-80 years. That is, at least doubled life expectancy. This was influenced, of course, by a combination of factors, but it was medicine that played a big role. And, for sure, 60-80 years is not the limit for a person average life. It is possible that someday people will cross the mark of 100 years. Scientists from all over the world are fighting for it.

In the field of other sciences, developments are constantly underway. Every year, scientists from all over the world make small discoveries, slowly moving humanity forward and improving our lives. Places untouched by man are being explored, first of all, of course, on our home planet. However, work is constantly taking place in space.

Among technology, robotics is especially rushing forward. An ideal intelligent robot is being created. Once upon a time, robots were an element of fantasy and nothing more. But already on this moment some corporations have real robots on staff that perform various functions and help optimize labor, save resources and perform dangerous activities for a person.

Still want Special attention to give electronic computers, which 50 years ago occupied great amount places were slow and required a whole team of employees to leave. And now such a machine, in almost every home, is already called more simply and briefly - a computer. Now they are not only compact, but also many times faster than their predecessors, and anyone can figure it out. With the advent of the computer, mankind has opened a new era, which many call "technological" or "information".

Remembering the computer, do not forget about the creation of the Internet. It also gave a huge result for humanity. This is an inexhaustible source of information, which is now available to almost everyone. It connects people from different continents and transmits information with lightning speed, it was impossible to even dream of such a thing 100 years ago.

In this section, you will certainly find something interesting, exciting and informative for yourself. Perhaps even someday you will be one of the first to know about a discovery that will not only change the world, but will turn your mind upside down.

I'll try again to clarify my opinion.
I was not talking about "bad" (Soviet) and "good" (Orthodox) people. I spoke about spiritual values ​​and ideals.
Historical Russia was formed, grew and developed in the Holy Spirit for a thousand years, and was based on the teachings of Christ. The Church and the values ​​it preaches to a large extent shaped the mentality and character of the Russian people. Unlike many other peoples, the very formation of the Russian nation took place with the participation of the Christian faith. Historical practice, of course, had various deviations from this ideal, but it itself was not disputed. So, historically, Orthodoxy was the very essence, base, foundation of Russia and the Russian people.
In contrast to Europe, which has been losing Christian values ​​and ideals gradually, over the course of almost a millennium, and where "debauchery", spiritual and moral indifference actually supplanted faith, and the place of the commandments of Christ in the soul of people "organically" was occupied by the clauses of the "Declaration of the Rights of Man", in Russia, de-Christianization was carried out in a historically short time, with monstrous violence and physical destruction of the bearers of the faith - the clergy and firmly believing laity. In us there is still no "hereditary", rooted in the souls of godlessness and indifference to the Truth. Deeply, mentally, "hereditarily" we yet, basically, - Christians - often, not even realizing this, illiterate, spiritually weak and confused.
Exactly this, potentially allows us, having been cleansed of alluvial debris, to return to the fundamental foundations of our spiritual and historical existence, to our God-given mission in the world.
There are, of course, obstacles to this. In addition to our laziness, the banal unwillingness to work at least a little spiritually, these include the psychological legacy of the Soviet period of history, as well as the increased introduction of Western ruminant-coca-cola mass pseudo-culture into our everyday life. Deprived of a conscious belief in God, having forgotten our history and traditions, weakened by the godlessness hammered into us, we are easily caught on this hook. In the course of time, these two factors mutate and change, and not a fiercely God-fighting, but a godlessly indifferent mentality, characteristic of modern “civilized” humanity, is formed.
Our generation, whose youth passed in a suffocating atmosphere of total Soviet lies and general duplicity and hypocrisy, is more focused on the search for the Ideal, the pursuit of Truth. Action gives birth to reaction. Forced godlessness aroused interest in God, striving for Him - even though through mistakes and delusions, but sincerely we tried to find Him, responded to His call addressed to every person.
The new generation is not forcibly taught godlessness, the faith of Christ has become in the minds of many a completely “conformal”, philistine phenomenon. This impression is completely wrong, but without the "experience" of faith, looking "from the outside", it is difficult to understand this. The fact remains: of course, not all of the new generation, but the vast majority of them acquire a ruminant-consumer psychology, and "nonconformists", passing by the faith of Christ, find themselves in a dead end, where all Western rock, hippie and punk "rebels".
In a few years, it is our “turning point” generation that will begin to exert a decisive influence on the fate of Russia. We will have a chance to change the vector of the country's historical movement. There are two options for development, as I already said: either a return to Orthodox roots, the foundation of the existence of the Russian statehood, or an infusion into the “global” world. In the first option, our country will regain its original spiritual principles, once again become a Christian state (i.e., a country in which different peoples profess different religions live, but which in its external activities professes Christian ideals at the state level). In the second case, Christians will remain a small minority (as it happens today in "civilized" countries), "marginals", "eccentrics" and "fanatics", whom a godless state may tolerate, but whose ideals (i.e. commandments Christ!) can never become basis for the existence of society.

What is in electrical engineering Do not directly connect copper and aluminum conductors, is not a secret even for many ordinary people who have nothing to do with electrics. From the side of the same inhabitants, the question is often asked to professional electricians: “Why?”.

Why chicks of any age are able to drive anyone into a dead end. Here is a similar case. A typical professional answer: “Why, why ... Because it will burn. Especially if the current is large. But this doesn't always help. Since this is often followed by another question: “Why will it burn? Why doesn't copper and steel burn, aluminum and steel don't burn, and aluminum and copper don't burn?

There are different answers to the last question. Here are some of them:

1) Aluminum and copper have different coefficients of thermal expansion. When a current passes through them, they expand in different ways, when the current stops, they cool down in different ways. As a result, a series of expansion-narrowing changes the geometry of the conductors, and the contact becomes loose. And then heating occurs in the place, it worsens even more, an electric arc appears, which completes the whole thing.

2) Aluminum forms an oxide non-conductive film on its surface, which worsens contact from the very beginning, and then the process is underway on the same increasing basis: heating, further deterioration of contact, arc and destruction.

3) Aluminum and copper form a "galvanic couple", which simply cannot help but overheat at the point of contact. And again heating, arc and so on.

Where is the truth, after all? What happens there, at the junction of copper and aluminum?

The first of the given answers all the same is inconsistent. Here are the tabular data on the linear coefficient of thermal expansion for metals used for electrical installation: copper - 16.6 * 10-6 m / (m * gr. Celsius); aluminum - 22.2 * 10-6m / (m * gr. Celsius); steel - 10.8 * 10-6m / (m * gr. Celsius).

Obviously, if it were a matter of expansion coefficients, then the most unreliable contact would be between a steel and aluminum conductor, because their expansion coefficients differ by a factor of two.

But even without tabular data, it is clear that differences in linear thermal expansion are relatively easily compensated for by using reliable clamps that create a constant pressure on the contact. Metals compressed, for example, with the help of a well-tightened bolted connection, can only expand to the side, and temperature changes are not able to seriously weaken the contact.

The option with an oxide film is also not entirely correct. After all, the same oxide film allows you to connect aluminum conductors with steel and with other aluminum conductors. Yes, of course, the use of a special lubricant against oxides is recommended, yes, a systematic revision of compounds involving aluminum is recommended. But all this is allowed and works for years.

But the version with a galvanic pair really has a right to exist. But here it still does not do without oxides. After all, the copper conductor is also quickly covered with oxide, with the only difference being that copper oxide more or less conducts current.

During electrolysis, ions transfer charges and move themselves. But, in addition, ions are, after all, particles of metal conductors. When they move, the metal is destroyed, shells and voids are formed. This is especially true for aluminum. Well, where there are voids and shells, it is no longer possible to have a reliable electrical contact. A bad contact starts to warm up, it gets even worse, and so on up to a fire.

Note that the more humid the surrounding air, the more intensively all of the above processes proceed. And uneven thermal expansion and a non-conductive layer of aluminum oxide are only aggravating factors, nothing more.

In addition to the article, there is a useful table that clearly shows the compatibility and incompatibility of individual metals and alloys when they are combined. Copper and aluminum cannot be connected to each other, as they are incompatible.

Note: C - compatible, H - incompatible, P - compatible when soldering, with direct connection form a galvanic pair.