Only two metals are widely used as conductors of electricity. Moreover, both in residential buildings and in industrial and industrial facilities. At the same time, aluminum wiring was popular mainly in Soviet times. In modern construction, this metal is prohibited for laying electrical communications, it is replaced by copper.
Half a century ago, the load on the electric network was not so great compared to today. Permanent attributes at that time were a refrigerator, a TV, several incandescent lamps. Families with a good income purchased vacuum cleaners, irons, floor lamps. All this perfectly withstood wiring with a cross section of 1.5 mm 2 .
However, progress is inexorably striding forward, it can no longer be stopped. Now, in almost every house there is a computer, which, depending on the characteristics, consumes not so little electricity. You can also add microwave ovens, automatic washing machines, and other modern television and household appliances.
In this regard, a reasonable question arises about the advisability in the further operation of aluminum wiring in an apartment or private house. Let's try to figure it out, but before that - a brief theoretical part.
Bit of theory
We all know from lessons in physics that electric current is the ordered movement of charged particles, which are the electrons acting on the forces of an electric field. these particles, moving along the conductor, inevitably encounter a reaction called resistance, measured in ohms (ohms).
And since the conductors have a cylindrical shape, the resistance calculation is carried out according to this formula: r = Ο * l / s, where:
- r is the electrical resistance of the conductor (Ohms);
- Ο is the electrical resistivity of the conductor material (Ohm * mm 2 / m);
- l is the length of the conductor (m);
- s is the cross-sectional area of ββthe conductor (mm 2 ).
It is for this reason that aluminum and copper are used - due to the low resistivity. In aluminum, r is 0.0294 Ohm * mm 2 / m, in copper it is slightly less than r - 0.0175 Ohm * mm 2 / m.
While the electric charges are moving along the aluminum wiring, it heats up. And the higher the resistance, the greater the heating. And it is not good. In addition, the temperature depends on another indicator - the current density, determined by the formula: Ξ΄ = I / s, where:
- Ξ΄ is the current density, (a / mm 2 );
- I is the magnitude of the current, (a);
- S is the cross-sectional area of ββthe conductor, (mm 2 )
What metal is best suited for the wiring of apartments and private houses? Consider the properties of aluminum and copper, and also analyze, perhaps, all the available advantages and disadvantages of each wiring.
Aluminum properties
The undoubted advantage of aluminum is its low weight. For this reason, the laying of such wiring is simple. The light weight of the metal is due to its low density, which is three times less than that of iron and copper. But at the same time, the strength of the 13th element is not inferior to them.
Along with electrical conductivity, the material also has high thermal conductivity. However, aluminum wiring cannot be heated very much, since the melting point of the metal is 660 Β° C. The 13th element of the periodic table of Mendeleev takes the third position in distribution in the earth's crust, giving priority to oxygen and silicon among all atoms. But in comparison with other metals, aluminum comes first.
Copper properties
Copper is a plate metal of a pinkish-red hue, like aluminum, it has high thermal and electrical conductivity. It melts at a temperature of 1083 Β° C, and boils at 2567 Β° C. The density of copper is 8.92 g / cm 3 . When interacting with air, a dense green-gray film forms, which protects the metal from further oxidation.
In nature, metal can be found in its pure form - nuggets in this case reach a weight of several tons. Also, copper can be found in other compounds. Often these are sulfides that form in sedimentary rocks or substrates. Copper can be easily obtained from these compounds due to its low melting point.
Comparing copper and aluminum wiring, it is impossible to ignore another property of this metal. Copper has a unique color like gold and osmium. But for electrical wiring, it is much more important that sparks do not occur upon impact. This property allows the use of metal in conditions of increased fire hazard.
Benefits of Aluminum Wiring
The most important advantage is, of course, the cost, which is available to many consumers. For this reason, in Soviet times, all residential facilities were equipped with aluminum wiring. Along with this, there are some more advantages:
- Light weight, which allows easy installation of power lines, especially when it is necessary to lay several tens or even hundreds of kilometers of wires.
- Aluminum is resistant to oxidative processes due to the formation of a protective film.
At the same time, there are also disadvantages, which will be discussed below.
The disadvantages of aluminum wiring
The characteristic disadvantage is the fragility of the metal. For this reason, wires often break when overheated.
Typically, the service life of aluminum wiring is no more than 30 years, after which the wiring needs to be updated. Among other minuses it is worth noting:
- High resistivity and tendency to heat. In this connection, it is not allowed to use wires with a cross section of less than 16 mm 2 for electrical wiring (PUE requirements, 7th edition).
- Due to the fact that the wires often heat up and cool down, contact joints loosen over time.
- That forming film, which protects the wires from oxidation, has a low electrical conductivity.
As you can see, there are still more weaknesses in aluminum wiring than advantages. Let's see how the situation with the use of copper.
The advantages of copper wiring
Aluminum wiring can withstand only a small load, a stronger current is undesirable for it. What can not be said about the analogue of copper. Its wires are resistant to bending, due to which they do not break off during long-term operation. In addition, it is worth noting improved electrical conductivity, and oxidative reactions in no way affect the performance of the entire wiring.
A copper wire with a cross section of 1 mm 2 is able to withstand a load of 2 kW. And this is two times higher than the aluminum counterpart. As for the service life, it is noticeably longer. If with aluminum wiring it is no more than 30 years, then with a copper analog - up to half a century.
The flexibility of copper wires makes installation much easier. In addition, such wiring is easiest to connect to electrical fittings (sockets, switches, etc.). And due to lower resistance, current losses are reduced 1.3 times.
Cons of copper wiring
The main and perhaps the only drawback of copper wiring is its high cost. If necessary, use technological wires, which have many cores enclosed in a special braid, the final price can be twice as much as the aluminum analog.
Can copper be combined with aluminum?
Sometimes it becomes necessary to replace not all of the aluminum wiring, but only part of it. In this case, when a copper conductor is selected, contact with an aluminum conductor cannot be avoided. With such a connection, there is a certain risk, which may result in an emergency.
The thing is that during operation, an oxide film forms on the wires, due to which the connection between the conductors is ensured. But each metal has its own electrochemical properties. Over time, the resistance increases, respectively, the wires heat up more, which ultimately can lead to fire.
Troubles can be avoided, and for this it is enough to adhere to certain rules for connecting aluminum and copper wiring:
- compound "nut";
- bolted connection;
- terminals
- pads.
This will avoid overheating at the junction of different conductors. Only in no case is it allowed to connect such a method as twisting, as this leads to overheating and - as a consequence - to a fire.
The connection "nuts"
Replacing the old aluminum wiring with a new one, you can use the option that has already passed the test of time. It got its specific name due to the use of special clamps.
The connection of wires is provided by special plates, which can be up to 3 pieces. The wires are secured with clamping bolts. It is noteworthy that with this method, direct contact of the conductors is excluded, since they are connected through plates.
Bolted connection
No less reliable is the connection of the wiring with a bolt. A bit like a nut, but there is a difference. Aluminum and copper wires are connected on one bolt, only a washer is placed between them to prevent direct contact between them. Then everything is securely fixed with a nut. In conclusion, the connection is well insulated.
Terminals
The use of WAGO-type spring terminals is suitable for applications where all wires must be replaced. Their main advantage is easy installation and ease of fastening of wires, due to the spring mechanism. Only before connecting the aluminum wiring to the copper one, you must first strip both conductors to a length of 13-15 mm from the edges. After that, it remains to place the wire in the mounting hole and fix it with a small lever.
It is only worth noting that you can use such terminals regarding wiring for lighting. A large load causes overheating of the springs and, as a result, the contact quality deteriorates. Accordingly, the conductivity decreases.
Pads
Using pads is one of the best ways to connect aluminum wires with copper. The connector looks like a strip made of a dielectric with metal strips and terminal blocks for clamping inside. All that is needed is to strip the wires well, insert them into the holes and press them down well with a clip.
This option is suitable when using high power consumers. The plates are thick enough to withstand heavy loads. Thanks to this connection, there are practically no equal.
Useful Tips
A few simple tips will help in deciding which wiring is better - copper or aluminum? A three-wire cable should go to the sockets (ground wire is required). At the same time, the distance from the outlet to the floor should be at least 300 mm. But for the wiring of lighting, you do not need to use a grounding wire, that is, two wires are enough.
It is highly recommended, especially in the case of aluminum wiring, to load only one circuit - it is necessary to divide it into several lines. For example, only a bathroom is connected to one machine, only a kitchen to another, the third is only responsible for lighting, etc.
In the course of self-designing wiring for your home or apartment, you should choose copper wires whenever possible. Firstly, with a smaller cross section, they withstand large currents and do not break with frequent bending. Secondly, it is about compactness. Take, for example, a consumer with a capacity of 7 or 8 kW. The aluminum conductor cross-section must not be less than 8 mm 2 . The cable will consist of three cores and a braid - as a result, the thickness of the wire increases to 4-5 cm. For a copper wire, the cross-section is smaller - 4 mm 2 , and the total thickness of the wire does not exceed 2 cm.