Cable lug - a structural element used when laying the tracks to create collapsible electrical connections. Metal of a vein strongly is oxidized. Especially for aluminum. Cable lug protects the cut against the action of oxygen, as well as other corrosive environmental factors.
Cable Tip Design and General Information
The cable tip material must conduct electrical current well. Otherwise, if the resistivity is large, the heat loss will be significant. In case of huge flowing currents, it can lead to fire, melting of the connection. During installation, special attention is paid to cleaning the metal surfaces of the cable lug and core.
Cable lugs are made of drawn( cold rolled) or extruded aluminum, copper tubes( see, for example, GOST 617).The standards spelled metal brand. In the course of the text, digressions are given, it is indicated: in addition to copper and aluminum, there are other alloys: tompac. Subsequently taken into account during installation. The addition of zinc to copper to obtain a tombac enhances the antifriction properties, reduces the cost of the product, while at the same time making it a little easier.
This is interesting! Tompak is clad with small coins of 10, 50 kopecks of issue in the second half of 2006-2015.
Samples are molded by pressing. It is easier to understand the picture below. It can be seen that the walls of the tube converge together, on the contact area the thickness of the material is doubled. We are interested in details, for example, in the GOST 7386 document. The type of cable lugs corresponds to the regulatory act. The specified applies to the copper range of lived cross-section of 2.5 - 300 square millimeters, voltages up to 35 kV.
The designation of the cable lug includes a size that defines the geometrical dimensions of the assembly connection. GOST 7386 indicates the cross section of the core, the flexibility class( GOST 22483, in the international classification - IEC 60228).Data is easily readable by cable labeling. Information GOST 7386 will allow you to choose the right tip size.
Installation of cable lugs
The main problem is oxide. A fresh cut of aluminum in minutes is covered with a film that has a melting point in the region of 2100 degrees Celsius. The conductivity of the oxide is small( widely used by semiconductor technology, see the topic field-effect transistor).The melting point of the film is high, the further process of installing the cable network is difficult. The following methods are used to overcome the problem:
- Contact welding.
- Gas welding.
Each technique has its own merits. Not without flaws.
Gas contact welding of cable lugs is not very useful today. The process is different from soldering: the material of the filler rod is mixed with the core. The fuel used is a mixture of oxygen with gasoline vapors, acetylene, propane.
Isolation is removed from the core at a given length, the paper is fixed with a bandage from the thread. The metal is stripped of oxide film. Contact welding is carried out with a carbon electrode. One feature is not to be missed: as a filler rod, we use wire of the cable being welded( previously cleared from the oxide film).
Crimping cable lugs will not require the use of complex process equipment. No need to bring electricity, look for gas cylinders, transport. Reduced requirements for personnel performing work( welding).
The main task at the initial stage is getting rid of oxide. The surface of the previously prepared gasoline-washed cable ends is covered with quartz-petroleum jelly, petroleum jelly. Then a metal brush crawl, removing the film. Ointment protects the surface from the influence of oxygen. An oxide is not formed. The inner surface of the cable lug must be coated with paste. The compression tool is used depending on the cross-section of the core, the method of crimping:
- hand-held tongs for local compression of a cross-section of less than 50 square millimeters;
- hydraulic press in other cases.
At the end of the crimping process, the excess paste is removed with a dry cloth, the insertion point of the conductor in the cable tip is coated with varnish and wrapped with insulating tape.
According to the old standards, we press the core up to 95 square millimeters with crimping. Modern mites have a different configuration of holes( usually traditional hexagon, a wedge), the range of sections is much wider( up to 300 square millimeters or more).The hydraulic tool is completely manual, does not require external power. Portable, convenient. Modern samples with a much wider range of compression profiles. Often we meet a circle, a trapezoid.
Hexagon and wedge are comparable to continuous and local compression( see fig.).The USSR used dies for the press, punches like the ones presented in the drawings. Taken from the literature of the last third of the 20th century( publications on the installation of cable systems sponsored by Proschina EA / Smirnova L.P. and Trunkovskiy L.E.).You can easily notice: for continuous crimping the shape of punches, dies was not always hexagon. The figure shows samples of a semicircular shape.
Dimensions for example only. Although RF standards are conservative, it is necessary to choose a tool with responsibility. Many samples are imported Chinese, may not meet the generally accepted standards of the state territory. When pressure testing we take into account the materials of the conductor, cable lug. The tool shown in the figures is used to press the aluminum conductors. You can use a range of matrices, punches aimed at copper cable lugs. The caliber is taken one more( for example, 25 instead of 16).
For soldering, welding, a cast tip is used, as shown in the figure. For aluminum, compounds with a high melting point close to the liquidus point of the metal are used. A burner is required, the process itself resembles welding. The use of typical solders will require pre-cleaning the surface with flux. It is possible to do with lower temperatures.
It is possible to heat the solder with a separate crucible( using Mosenergo).Of refractory solders, we note aluminum-silicon, copper-phosphorus, copper-zinc, copper. In the process it is important to maintain a given temperature. Provided with soldering stations. If conditions allow, equipment can be used. Previously, the process was difficult, the temperature was determined by the color of the flux, the conditions of spreading solder. Shareholder required considerable experience.
As for the process, it could look like this for an aluminum conductor:
- The cable is cut in steps to the top insulation: 10 mm indent is taken for each layer.
- The core is heated to solder temperature( determined by composition).
- The master holds a gasoline burner in one hand, a brush with metal bristles and a solder rod in the other.
At the same time, it is necessary to heat the core, scrub it with a brush, and gradually cover it with solder. With copper it is simpler, the cable lug is mounted as follows:
- The copper lug is clamped with a vice, bowl up. Inside the solder is laid. The
- is heated to the melting point of the solder together with a blowtorch.
- The cleaned, previously preserved vein is lowered inward, it is necessary to wait for cooling, without easing the pressure on the cable.
Here to note, craftsmen often use standard tips. Intended for crimping. Do I need to strip out of oxide? Of course, rosin is suitable for copper, aluminum needs to be treated with flux. The vein should be tinned.
Copper is not so quickly covered with oxide. Although it is more expensive, problems during installation arise much less. For copper, the electrochemical corrosion process is safe. Will not collapse in case of accidental contact with water. Equal to other electrolytes. Solder can also be taken cheap. For example, POS 30.
. NSHVI tips.
. Insulated pin bushings, insulated, are often referred to as cable ties. Designed for screw, clamping connections. Like those found in ordinary sockets, switches. And if the wire with high flexibility conductors consisting of many small wires, without NSWI, the product with a high degree of probability will break into small pieces. In such cases, it is not possible to tighten a screw of thin, brittle copper threads with a screw.
The NShVI tip is cylindrical and is put on the core with crimping. After the cable( wire) can be clamped with a screw, a latch without losing the conductive properties of the connection.
Note: the zealous owner can solder the end of the flexible core to solder or switch.
Can be used sleeves. If there is a need to combine copper, aluminum wires, a bimetallic specimen is taken. It is necessary in cases when there is a need to avoid electrochemical corrosion. Note: even in dry rooms, the effect of condensation is possible. Naturally cause the destruction of aluminum in contact with copper, an increase in contact resistance to electrical current. Under certain circumstances, will cause a fire.
How to choose
The choice is reasonable to carry out, having previously found the GOST of the desired type of cable lugs. For example, for copper-aluminum TAM will be GOST 9581. Further it is clear from the above:
- according to the tables of the standard, the desired size of the cable lug( corresponding to the cross section of the core) is found;
- is then decoded labeling( product parameters are obvious to the inexperienced user).
The tool is configured according to the manufacturer's documentation( user manual).GOST 25346( Unified system of tolerances and landings) is unable to answer the question of how to use the installation tool.
It is reasonable to pre-assess the scope of work, tongs for crimping different sizes. Should choose( based on price) the most profitable option. It may be that some cable lugs are conveniently crimped, others are soldered( it was agreed: welding as of today is rarely used).
Avoid buying from a random seller of electricians for high-powered networks. If we are talking about a private house, where the currents are small, nothing terrible, you can save. In other cases, stinginess can lead to a fire. There is no certainty that it will be possible to distinguish tomback from bronze, copper, brass, the requirements of regulatory acts are unclear, wait a little risk.