Uninterrupted power supply is possible only with a reliable connection of electrical wires. Often, twisting technology is used for this purpose. But the wires connected in this way are prone to overheating and oxidation. Due to the incompatible electrochemical properties of metals, it is undesirable to twist aluminum and copper wires. In such cases, crimping with liners is recommended.
GMF - what is it?
To connect electrical wires from copper by the method of twisting, copper sleeves are used. The acronym GM refers to a conventional, without any coating, copper sleeve. GML is a copper sleeve that has passed the tinning procedure. A special tin-bismuth layer is applied to it. This is especially necessary for products made of copper, as this material is prone to oxidation.
Due to this coating, tinned copper sleeves are not subject to corrosive processes and do not react with conductors. These products are not recommended for use in electrical work in conjunction with aluminum wires. This is explained by the fact that during compression the protective coating can break down, and the GDF sleeve will enter into a chemical reaction with aluminum.
Types of liners
Connecting sleeves can be of such types:
- GA. Under this abbreviation is a sleeve made of aluminum. This type is used to connect exclusively aluminum wires.
- GAM. This is a combined type. Often such gizzi are also called aluminum-copper. Used for butt joints of aluminum and copper wires (building in old wiring). Since aluminum has a greater resistance than copper, the aluminum part is produced with an increased diameter in products of the GAM type.
- GSI. Insulated connecting sleeves are tinned products coated with polyvinyl chloride insulation. They are used to connect stranded copper wires. During crimping, insulation is not removed. Press with the help of special ticks can be done directly through the coating.
Pipes for connecting power cables
Cable sleeves are used for mounting cables in instrumentation, switchboards and mechanical engineering. They provide good contact during installation and prevent separation of the cable cores during its use.
Cable sleeves are highly resistant to deformation and protect the wire from mechanical damage. This significantly extends the operational life of the product.
Types of cable sleeves
Depending on the method of mounting the sleeves are intended:
- For crimping. Installation is carried out using cable presses.
- For soldering. Compared to crimping, this connection method is more time consuming.
- For bolting. Work is carried out without using a special tool.
GML sleeve section
Sizes and range of sections are shown in the table. The standard minimum cross-section is 1.5 square meters. mm Next is increasing: 2.5 square meters. mm, 4-6-10 sq. mm Tinned copper sleeves with their parameters correspond to the cross section of the wire. Professional electricians use simplified names: "fours", "tens", etc. The "Six" is a tinned copper sleeve having a 6-mm minimum cross-section. GML-6 - such a designation can be seen in the technical documentation.
In what cases use the "six"?
According to its characteristics, the GML-6 sleeve can freely pass four electric wires through itself, having a minimum cross-section of 1.5 square meters. mm With a cross section of 2.5 square meters. mm no more than three such wires will enter this sleeve. The fourth can be used as a sealant. The minimum cross-section of this wire should be 1.5 square meters. mm In addition, the “six” can be used for crimping two wires with a cross section of 2.5 square meters. mm
Sleeve design
Depending on the design, the GML sleeve can be:
- Through. Such a sleeve is a hollow tube.
- Containing a septum in the middle of the tube. This type is used for butt joints. You can adjust the depth of approach of the connected cables using the data of the GML sleeve. It is recommended to connect extended (extended) wires using tubes equipped with partitions.
Product Specifications (GOST 23469.3-79)
- Type of product - tinned copper sleeve. Intended for connection by crimping wires and cables made of copper. The product is processed by the method of tin-bismuth tinning. As a result, the sleeve acquires a white tint. Designed for voltages not exceeding 10 kV
- The design of the sleeve is end-to-end. According to the inner and outer diameter, the product corresponds to the tips of GOST 7386.
- GML are designed for connecting cables and wires (flexibility classes 5 and 6). In order to carry out the electrical installation of cores made of copper of class 2 or 3, you will need a tinned copper sleeve, the size of which can be selected using a special table.
The principle of crimping
Crimping is a process in which electrical wires are connected using special sleeves. The functions of the connecting mechanisms are performed by metal tubes (sleeves) into which wires are pushed from both sides.
The principle of crimping is to compress the sleeve with the wires in it using press tongs. In everyday life, this special tool can be replaced with pliers or a hammer. Compression is done in several places. After that, the sleeves are insulated using a heat shrink tube or PVC insulating tape. This step can be skipped if a ready-made insulated connecting sleeve is used.
Stages
It is not difficult to crimp using sleeves if you follow the step by step instructions:
- You need to decide what type of shells will be used. The material of the wire must match the material of the sleeve. It is undesirable to use copper connecting means for cables made of aluminum, since their chemical interaction can occur, which will lead to oxidation and a decrease in electrical conductivity.
- Treat the inside of the sleeve using quartz-petroleum jelly pastes.
- Prepare the cores of the cables to be connected. For this, insulation is removed from the wires. The length of this section should correspond to the length of the sleeve. If the crimping procedure is used for shaped wires (their cross section is oval or rectangular), then these cores must be rounded to the geometry of the connecting sleeve.
- After removing insulation, conductors must be cleaned. At the end of this stage, the surface of the wire should acquire a metallic luster.
- Treat the cleaned surface of the wire with quartz-vaseline paste.
- Fit the connection sleeve onto the prepared wires. During this work, it is important to ensure that the ends of the connected wires are docked to each other in the center of the sleeve.
- To pressure test. Work is carried out by reciprocating the upper handle of a special press. The action should be performed until the matrices are in full contact. It is important that the working area of the ticks matches the size of the sleeve.
- Insulate the junction. For this, you can use electrical tape. Also, the heat shrink tube will cope with this task. In this case, the connected wires are passed through it at the very beginning of the work. It is easy to solder a tube, using the construction hair dryer.
In what cases is crimping used?
This technology using GMF can be used:
- for connecting wires in a line with a high load.
- When connecting wires with a large cross section.
- In cases where it is not possible to apply any other type of connection.
The most common crimping errors
Often, some craftsmen, not having at hand special pliers for crimping, use ordinary pliers, a chisel and a hammer to crimp. This is not recommended, as the pliers are equipped with special dies, punches and jaws, providing high-quality crimping. Often, wires connected in a tinned copper sleeve using pliers, after a while they fall out of it. Today, the tool market offers a wide range of manual or electric crimping pliers.
In the absence of a tinned copper connecting sleeve of the required size, a copper tube may be used. The masters leave the free space between the core and the wall of the copper tube with pieces of other wires. It is important that these pieces are of the same metal as the pipe. This requirement applies to both copper pipes and aluminum. However, there is a big difference between the electrotechnical material in this sleeve and the material in the home-made tube material. Therefore, for crimping, it is best to purchase a connecting tool made of a special grade of metal. In the case of GMF, it will be electrotechnical copper.
Often, having bought a GMF with the wrong cross section, some consumers cut off part of the conductor. This mainly happens in cases where the cross section of a tinned copper sleeve is smaller than that of a core. Cutting is not recommended, since a reduced cross-section in the wire will create a mechanically vulnerable spot on it where breakage can occur.
After unsuccessfully selected too large GMF during the connection of stranded wires, they can not be folded in half and thrust into the sleeve. This connection will not give mechanical strength. Contact will remain unreliable. To connect the wires using crimping, you do not need to use a soldering iron or welding machine. For work, you only need special mites. They are easy to work in the most inaccessible places. Tinned copper sleeves, as well as similar products of other types, have recently become increasingly popular.