Most common people are well aware that aluminum and copper conductors cannot be connected directly to each other. But at the same time, the reasons for such a ban remain incomprehensible to them. Let's try to figure this out.
The explanation can begin with the fact that the thermal expansion coefficient of these metals is different. They expand differently with the passage of electric current. They also cool at different speeds. The contacts break up and become not dense, since the geometry of the conductors changes during many extensions and contractions. Further, in the place of broken contact, high temperature occurs.
The electric arc becomes the logical result of the constant use of copper and aluminum conductors directly.
It is also worth noting that an oxide non-conductive film covers completely the entire surface of aluminum. Contact, it worsens with increasing effect. The connection is heated, the contact is broken, an arc occurs, the wiring is destroyed. These two metals will necessarily overheat at the point of contact, since they form the so-called “galvanic pair”.
These are common answers to questions about why aluminum and copper conductors cannot be connected. But at the same time, not all of them are wealthy. In particular, many questions from specialists can arise for the first explanation. Reliable clamps providing constant pressure to the contact can solve this problem. A well-tightened fastener prevents the materials from expanding too much. Contact does not weaken due to constant temperature changes.
It is also impossible to call a completely true version in which the oxide film is to blame. Similar aluminum conductors are connected to other aluminum conductors without any problems. Yes, of course, it is recommended to reduce oxides with a special lubricant, yes, aluminum compounds must be checked periodically. But there is no ban on the use of such contacts, everything can work for years.
The most true version is the one in which the galvanic couple is mentioned. But oxides play a role in this explanation as well. Conductors made of copper are oxidized quickly enough, but they conduct current. Oxides of aluminum and copper create dissociation in the contact, that is, they decompose into charged ions. Natural moisture present in the air is enough to start this process. As a result, electrolysis begins, during which charges are carried by ions during the movement. Voids are formed during the destruction of the metal during this process. Electrical contact is broken.
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