Making a reliable electrical contact when installing a cable is not as easy as it seems. This is especially true for aluminum wires: due to the physical properties of the metal, problems can arise when connecting them.
Features of aluminum wires
According to the rules of the PUE, it is forbidden to use aluminum conductors during installation in residential premises.
Aluminum wire is a cheap solution, which has an order of magnitude lower price compared to copper. It does not corrode, as it instantly becomes covered with a thick oxide film. It has a low specific gravity.
The main disadvantage is the low electrical conductivity of aluminum. It is 37.9 μS × m, which is almost two times worse than copper, which has 59.5 μS × m. The low flexibility of the conductor makes it impossible to install in places where it is exposed to repeated mechanical stress.
There are four types of wire connection: crimping, compression, welding, soldering. Crimping sleeves and terminal blocks provide easy and quick cable installation in places where high mechanical resistance is not required. Soldering and welding will give the most durable and reliable connection, but they require skill and the use of special tools.
Pressing method
Pressing is carried out using a special sleeve, into which the veins are inserted, after which they are crimped with a special tool - a crimper. The sleeves differ in diameter, length and material of execution. When installing the cable, use only aluminum or brass sleeves. Using brass elements, it is possible to connect both aluminum to aluminum and copper to aluminum wires.
When connecting aluminum conductors, copper-containing sleeves must not be used. These two metals form a galvanic pair, which leads to accelerated destruction of aluminum.
To connect conductors with different cross-sections, special sleeves with different diameters of inlet holes are used.
The correct choice of the diameter of the sleeve will protect the chain section from overheating. A larger diameter will give a small contact patch and an increase in resistance. If the cross-section of the sleeve is smaller, it is necessary to reduce the cross-section of the cores, which will also negatively affect the conductive properties.
Compression method
When routing a cable in a junction box, accidental contact of adjacent conductors is highly undesirable. Terminal blocks are used for this purpose.
The terminal is an insulated sleeve into which the wires are inserted. Inside, either a screw or a spring is used to fix it.
If it is intended to install a stranded wire, before installing it in the terminal, it is necessary to crimp it with a special sleeve, which will improve the contact and reduce the likelihood of pinching.
Using terminals with screw connection, it is necessary to clearly control the clamping force in order to avoid cutting the core with the screw and its subsequent destruction. The Wago terminal blocks are devoid of this drawback. In them, the core fixation mechanism is a brass plate and a spring. The use of brass in the composition makes it possible to safely connect cables of different metals.
Welding method
Welding provides the best electrical contact. Due to the homogeneity of the connection obtained, there is no problem of increased resistance of the circuit section.
A welding machine is used with an output power of up to 1 kW and an adjustable voltage in the range of 14-20 V.Welding is considered successful if a drop is formed at the end of the twist, with a diameter approximately equal to the twist.
When welding at the end, the strands are carried out with a carbon conductor. The exposure time should not exceed 2 seconds.
There is an option for gas welding of wires. In an inert gas atmosphere, an oxide film ceases to form, which greatly facilitates the process, but specific knowledge and equipment are required.
Soldering method
Before tinning the surface, remove the oxide film. This can be done either by mechanical action, for example, with sandpaper or a brush with metal bristles, or with the help of a special chemical - flux. It is a white powder that dissolves in water, after which it is applied to the ends of the tinned veins.
Oxidation of aluminum in air occurs in a matter of seconds, so it will not be possible to remove oxides by mechanical action alone. It is recommended to combine the use of flux and surface cleaning.
If two cores are soldered, a 60 W soldering iron will suffice. For wires with a large cross-section and when soldering stranded twists, you will need a soldering iron with a power of 150 watts or more.
The tin in the solder must be at least 50%. You can take solder with 60-90% content.
Soldering aluminum in steps:
- Degrease the surface. Gasoline, alcohol will do. This will thin the oxide film.
- Fix the wires in the required position.
- Apply flux. Make sure it is caught in the joint of the cables.
- Warm up the twist with a soldering iron or gas torch. In the latter case, you should be careful, as the metal heats up quickly and can melt.
- Tinker the junction. Gently grind the solder with a soldering iron until a uniform shiny film appears.
A properly treated surface will acquire a characteristic metallic sheen. The appearance of sagging and non-tinned areas should not be allowed.
Tin solder is susceptible to corrosion, so the finished joint is treated with varnish.
When extending wires, if operation is expected in difficult conditions, a soldered or welded joint will show itself best. In everyday life, for cables that are not subject to mechanical stress, crimping with a sleeve is quite suitable.
