How to connect copper and aluminum wires

I met working copper-aluminum twists of 20 years ago without any signs of oxidation. In the old buildings.

Many people mistakenly believe that the combination of copper and aluminum creates a hypothetical galvanic vapor and due to their mutual oxidation, this compound becomes unusable. This is not entirely true.

The point is the different density and electrical conductivity of these two metals. In a copper-aluminum pair, when the current flows through it, the following occurs:

- Both copper and aluminum, like any other metal, heat up when they pass through them and, accordingly, expand slightly. But copper is a harder metal and, when expanded, it deforms aluminum and compresses it. When the load is disconnected, both metals cool and, pepper is clear, they take their former dimensions. But the next time the load is turned on, the current will pass through the "chilling" connection. But to avoid this, it is often enough to combine them under a grover. At low load currents, copper-aluminum compounds last for a long time.

Sonvos, galvanic steam is not hypothetical, it is real, but it manifests itself when exposed to moisture. If the room is dry, or good insulation, then there will be no problems with a copper-aluminum pair. Here we have two lighting risers with aluminum wires diverge into six switchboards with copper tires - direct contact, 30 years worth and no oxidation of the compounds. But it’s dry in the room and there was such a “flower bed” on the street signs that it had already changed aluminum to copper for a long time. It is not a matter of electrical conductivity, but of the difference in the electrochemical potentials of metals. For example, in a damp room, the contact of a copper conductor with a galvanized washer will decay much faster than the contact of a copper-aluminum pair.

I agree with Vadim. As soon as the neighbors fill the box, even with small currents on the twists, a high-speed chemical process begins. And if ampere 10 - instantly crumble.

And how to connect the wire from the hob with the wire intended for it in the wall? There are special sockets designed for a large number of amperes, but unfortunately they take up a lot of space. Can such connections be made using nut-type terminal blocks, how much are they designed for? Or is there something better in quality?

He opened the twist 9 years ago. On a copper wire, the insulation is destroyed, everything is covered with oxides, the aluminum wire is unchanged. The twist was in a damp place, the load of the electric motor is 1 kW. At the time of the autopsy, everything worked without complaints.

Electrician, how many times the wiring changed the old one, in all cases the twists of aluminum and copper wires were in unsatisfactory condition. The twisted conductors are covered with a layer of oxide, the insulation that was wound on the twist is completely melted due to the fact that the twist was very hot. And this despite the fact that the load was relatively small. In addition, the insulation of twisted conductors is fused near the twist, and in a section up to 10 cm from the twist in such a state that it breaks up at the slightest bend of the wire. The only exception is the twisting of the aluminum and copper conductors of the apartment lighting wiring line. The load on this line is not more than three amperes, respectively, the twist did not heat up and after a few years provided a normal contact connection. And those twists of aluminum and copper conductors, along which a large load flows, as a rule, do not live long.

In practice, ALL Al-Cu compounds turn into rubbish after a fairly short period of time. In one case there was a fire! So it’s better to forget about such twists!

I solder a copper wire with a soldering iron and through the twisting of aluminum and tinned copper I make an electrical contact. For about 10 years, a refrigerator, an electric stove, a washing machine, etc. / sockets for an electric kettle, a boiler / have been connected to such wiring. At the same time I use - a washing machine, a refrigerator, an electric stove up to 0.5 kW.

Many describe cases of long work of copper-aluminum twists. Such a twist will work, but it is not known what time it is. That is, about any reliability of the wiring of speech can not go. It is better not to take risks, not to check how many years such contact connection will last, but to exclude such connections. Do not build up old aluminum wiring lines, but replace them. Or, if necessary, connect copper and aluminum wires to use terminal blocks.

vladimir,
This method can be used if there are no jumpers or the bolted connection does not fit in the box. However, for an electrical cable with significant loads, such a connection cannot be used.

One-piece connection is made using a special tool - a rivet.

The wire connection technology is as follows:

Remove insulation from conductors (cleaning length is equal to 4 diameters of future rings). It is optimal if the diameter of the ringlets slightly exceeds the diameter of the rivet.

Twist the rings from the cleaned ends of the wire.

Put on the rivet all the elements in the following sequence:

aluminum wire;

spring washer;

copper wire;

flat washer.

Insert the steel rod into the riveter and squeeze its handles until a distinctive click is heard.

The exposed sections of the joint must be isolated.

The reliability of one-piece connection is very high, the only drawback is that there is no way to disconnect and re-fasten the wires.

Aluminum, like copper, oxidizes in air (combines with atmospheric oxygen) and an oxide film appears on its surface. In copper, under normal conditions, an oxide film forms slowly, it is easily removed and has a negligible effect on the deterioration of the contact compound. A film of alumina is formed in the air very quickly, has greater hardness and significant electrical resistance, as a result of which the state of the contact compound deteriorates rapidly. The film of aluminum oxide is refractory (the melting temperature of the film is about 2,000 * C, aluminum 565-678 * C) and prevents soldering and welding.

Aluminum has a low yield strength. It means. that aluminum, which is under a pressure greater than a certain value, begins to flow from a region with a high pressure to neighboring ones that are under a lower pressure. From this it follows that if the aluminum contact joint is tightened excessively with a bolt, then over time the contact joint will weaken due to the fact that some part of the metal "leaks" into neighboring areas under less pressure.
Aluminum, when combined with copper and other metals, forms a galvanic pair, as a result of which aluminum is destroyed by electrochemical corrosion. This circumstance has an important effect on the deterioration of contacts in the compounds. Imagine an enlarged view of the contact compound of copper and aluminum. Even with the most careful processing of the contact surfaces, the actual touch (contact) will take place only at individual points. Between the points of contact there will remain voids, oxides of the metals to be joined, and other contaminants which, with a certain combination, can form an electrolyte. Thus, with electrodes of different metals, the presence of an electrolyte between them and a circuit closed at points between the electrodes will circulate currents, and this will lead to a gradual destruction of aluminum and, naturally, deterioration of the contact compound.

In the case of contact of aluminum with another metal, to prevent the destruction of aluminum from electrochemical corrosion, it is necessary either to cover both contact surfaces with some third metal or alloy (for example, tin, then there will be contact between the metals of the same name), or to prevent air and moisture from entering the voids between contact wheelbarrows.The latter can be achieved, for example, by coating the contact surfaces before assembling them with acid-free petroleum jelly.

They would remove the pictures of terminal blocks with levers - such ONLY for copper.

Under aluminum - one-piece with a paste inside.

Just the facts: yesterday the phase burned out (it’s good that it’s not zero) in the apartment building due to heating in the terminal block U734 M U3 of the "nut" type. A copper multi-wire wire with a cross section of 10 kV and an aluminum 8-wire wire were docked in it. The connection was mounted 14 months ago, tightened well, in the phase of 9 apartments, the copper wire burned out. On a separator plate made of "nut" in the center, there is a swelling of metal with a diameter of 6 mm and a 2 mm hole as if copper diffused through the aluminum. No corrosion was found anywhere.
As you know, this plate is made of stainless steel, and it has a specific electrical resistance of 3.5% of copper, although the current can flow and bypassing the stainless steel by screws. The connection is located, although in the room, but in the immediate vicinity of the front door (4 meters), from where moist air comes from the street, now it is a thaw.
The emergency workers restored the riser through a bolt under the nut, and iron washers were laid between the wires. I thought to process all the nuts with silicone in aerosols.