Technology of crimping wires with sleeves Automatic translate

Crimping of wires with sleeves is a method of creating an electrical connection by mechanically compressing a special metal tube (sleeve) around the conductors. This technology ensures high strength of the connection, good electrical conductivity and is widely used in electrical installation work.

The principle of operation of crimping

The physical basis of crimping is the deformation of the metal sleeve and conductor under high pressure. During the compression process, the oxide layers on the surface of the metals are destroyed, which ensures a gas-tight connection with high conductivity.

Research shows that the mechanical strength of the connection reaches its maximum when the total cross-sectional area of ​​the metal is reduced by approximately 10%. If the compression is too strong, the wire threads are deformed and destroyed, and if it is not strong enough, the wire may jump out of the sleeve.

Interestingly, the maximum electrical conductivity occurs at a compression of about 30%, but at this pressure the mechanical strength of the materials is significantly reduced. Therefore, the optimal crimping is a compromise between electrical requirements and mechanical characteristics.

For most connector types, the optimum compression ratio is in the range of 10-20% of the original cross-section. This provides a balance between the strength of the connection and its electrical conductivity.

Types of crimping sleeves

Selecting the appropriate type of sleeve is a critical step in the crimping process. The sleeve material must match the material of the conductors being connected, otherwise there is a risk of electrochemical corrosion.

Copper sleeves

Copper sleeves (GM) are used exclusively for connecting copper wires. They are made of refined copper grade M1 (according to DIN standard) or electrical copper grade M2 ​​(according to GOST standard).

These cartridges do not have a protective coating, so they are recommended for use in non-aggressive conditions. If this rule is not followed, the cartridge quickly oxidizes and loses its properties.

Tinned copper sleeves

Tinned copper sleeves (GML) are designed to connect copper wires used in conditions of high humidity or aggressive environments. They are coated with a special tin-bismuth composition that protects copper from corrosion.

Such sleeves are absolutely not suitable for crimping aluminum wires due to the risk of electrochemical pair formation, leading to increased corrosion.

Aluminum sleeves

Aluminum sleeves (GA) are made of electrical aluminum grade AD1M and are intended exclusively for connecting aluminum wires. When working with them, special attention is required: regular lubrication and cleaning of contact surfaces.

Tubular terminals are used to terminate aluminum cores with a cross-section of 16 to 240 mm² of wires with a voltage of up to 2 kV and cables with a voltage of up to 35 kV, and ring terminals (pistons) are used for cores with a cross-section of 2.5 mm² of wires with a voltage of up to 2 kV and cables with a voltage of up to 1 kV.

Combined sleeves

Combined (aluminum-copper) sleeves (GAM) are designed specifically for connecting dissimilar conductors - copper with aluminum. Such sleeves have a unique design: one half is made of aluminum, the other - of copper.

Both parts are connected by friction welding, which eliminates direct contact between different metals and prevents electrochemical corrosion. A special limiter is located at the connection points, preventing contact between dissimilar wires.

Insulated sleeves

Insulated sleeves for crimping wires are supplied with already built-in protective insulation at the contact points. The insulation layer is usually made of high-strength polymer materials. Such sleeves allow to simplify the installation process significantly, since there is no need for additional insulation of the connection point after crimping.

Crimping tools

The quality of crimping directly depends on the correct choice of tool. The modern market offers a wide range of devices for this purpose, differing in the principle of operation and technical characteristics.

Mechanical press pliers

Mechanical crimping tools such as crimpers and press pliers are characterized by a simple and reliable design. They do not require special maintenance and are relatively inexpensive.

Although mechanical tools are less productive compared to other types, for small volumes of work and crimping of small cross-section tips (from 1.5 to 10 mm²), a compact mechanical press is very convenient and effective.

The principle of wedge-shaped pressing (pressing) is most often implemented in mechanical pressing pliers. This method is considered a reliable alternative to soldering, especially when installing cables with solid-drawn mono-cores.

Hydraulic presses

The hydraulic tool multiplies the force of the hands with the help of a hydraulic system. Such devices are capable of creating a pressing force from 5 to 100 tons, which allows working with cables of the largest cross-section.

Hydraulic presses are most often used for hexagonal (hexagonal) crimping – the most popular technique for installing cable sleeves and tips. The hexagonal profile of the dies ensures uniform crimping of the tip shank along the entire perimeter, maximum contact area and a high degree of sealing.

Electrohydraulic tools

The electrohydraulic tool is equipped with a motor with an electronic control board and batteries. Such devices make the crimping process much easier and faster.

The main advantages of electrohydraulic presses are their compact size and light weight compared to conventional hydraulic models. This is especially important when performing large volumes of work or when installing in hard-to-reach places.

Crimping using explosive energy

Crimping using explosive energy is a specialized method used primarily in the construction of power transmission lines. This technology is used for crimping connecting, loop, tension, branch and repair clamps when connecting large-section steel-aluminum wires (AC 240 - AC 500).

This method uses standard clamps (e.g. tension clamps type HAC or connecting clamps type SAC), which are pre-treated by mechanical processing. The explosive charge is located on the clamp body, and a protective layer of polyethylene film or rubber is used to protect the surface of the connector.

The quality of crimping of clamps using explosive energy exceeds the results obtained using traditional pressing equipment.

Technology of performing pressure testing

Correct crimping is a sequence of specific actions, each of which is critical to obtaining a reliable connection.

Preparing the wires

The first stage is preparing the wires. It is necessary to remove the insulation from the end of the wire to a length corresponding to the size of the sleeve. Then the ends of the wires are carefully cleaned to a metallic shine to remove the oxide film, which can worsen the electrical contact.

Cleaning can be done with cord tape brushes, sandpaper or special tools. After cleaning, the wires are wiped with a rag soaked in gasoline to remove any remaining dirt and grease stains.

Before crimping, it is recommended to coat the stripped ends of the wires with quartz-vaseline paste to prevent oxidation and improve contact.

Selecting a sleeve

The choice of a suitable sleeve depends on the material of the conductors being connected, their cross-section and operating conditions. It is essential that the sleeve be made of the same material as the conductors being connected, or be combined when connecting dissimilar metals.

The size of the sleeve must exactly match the cross-section of the wires being connected. If the sleeve is too big, the connection will be unreliable; if it is too small, the wires may be damaged during crimping.

Before use, it is necessary to check the presence and quality of the factory grease in the sleeves and tips. In the absence or deterioration of the condition of the factory grease, the sleeves are cleaned with a metal brush and lubricated with a layer of zinc-vaseline or other suitable paste.

The crimping process

After preparing the wires and selecting the sleeve, the stripped ends of the wires are inserted into the sleeve as tightly as possible so that there are no empty spaces. When connecting several conductors of the same cross-section, possible empty spaces can be filled with additional pieces of the same wire.

When connecting two wires with a sleeve, it is necessary that the cores touch each other in the middle of the sleeve. When terminating a wire with a tip, the core is inserted until it stops.

The sleeve is then crimped using a crimping pliers or other specialized tool. The crimping should be done at least in two or three points, with the pliers turning 90 degrees in each new crimp to ensure uniform deformation.

The residual thickness of the sleeve at the pressing site must comply with the standard values. If the pressing depth is insufficient, the pressing should be repeated, after first making sure that the matrix and punch are selected correctly.

Connection insulation

After successful crimping, the connection point must be insulated. Various materials can be used for this: heat-shrinkable tubes (heat shrink), insulating tape or special insulating caps.

Heat shrink is considered the most reliable method of insulation, providing a high degree of connection protection. When using insulating tape, it is wound with a 50% overlap in three layers, and each layer is recommended to be covered with moisture-resistant varnish.

Small pieces of insulating tape, also coated with moisture-resistant varnish, can be placed into the depressions for additional protection.

Crimping methods

There are several methods of crimping, each of which has its own characteristics and areas of application.

Crimping by local pressing method

When pressing by local pressing with the punch teeth in one or more places, significant pressure is created, forming a point electrical contact. This method is widely used when working with mechanical pressing pliers.

The advantage of this method is the simplicity of execution and the ability to work with a compact tool. However, contact is not created over the entire area of ​​the connection, which can reduce its reliability under high loads.

Crimping by continuous crimping

In continuous crimping, the pressure is distributed evenly over the entire contact area. This method is more often used with hydraulic tools and provides a more even distribution of the load.

This method provides high stability of electrical contact and mechanical strength of the connection. It is especially effective when working with large cross-section wires and under variable load conditions.

Crimping with combined crimping

Combined compression combines the advantages of both of the above methods. With this method, continuous compression is first created over the entire contact area, and then additionally high-pressure zones are formed in the places where the punch teeth are pressed in.

The result is an optimal combination of electrical conductivity and mechanical strength of the connection. This method is especially recommended for critical connections in power circuits with high current loads.

Advantages and disadvantages of crimping

The technology of crimping wires with sleeves has a number of significant advantages, but is also characterized by some limitations that must be taken into account when choosing a connection method.

Advantages of crimping

The main advantage of crimping is the high mechanical strength and reliability of the contact created. A correctly executed connection is capable of withstanding significant mechanical loads without losing electrical conductivity.

The pressed connection is resistant to vibration, impact and temperature changes, making it ideal for conditions with variable loads. This is especially important when installing power lines and power supply circuits for powerful equipment.

Electrical reliability is another important advantage. Correctly pressed sleeves provide a stable electrical connection with minimal transition resistance. This reduces heat generation at the point of contact and increases the overall efficiency of the electrical system.

An additional advantage is the ability to connect conductors made of different metals (aluminum and copper) using special combined sleeves. This is a serious advantage, given that direct connection of these metals causes active electrochemical corrosion.

It is also important that crimping fully complies with the requirements of regulatory documents (PUE) and is recognized as one of the most reliable methods of connecting wires.

Disadvantages of crimping

The main disadvantage of crimping is the inseparability of the created connection. If an error is made during installation, the only solution is to cut the sleeve and make the connection again. Therefore, during installation, it is necessary to leave a sufficient supply of wire.

Another limitation is the need to use a special tool for high-quality crimping. Attempts to crimp with tools not intended for this purpose (for example, pliers) can lead to a poor-quality connection and a subsequent emergency situation.

Also, certain skills and knowledge of the technology are required to perform crimping correctly. Inexperienced fitters can make mistakes that reduce the reliability of the connection, even when using the right tool.

Application areas

Crimping wires with sleeves is used in many areas where it is necessary to create a reliable electrical connection.

In household wiring, crimping is widely used when connecting wires in junction boxes, especially if a significant current will flow through the connection, such as for a hob or socket block.

In industrial electrical engineering, crimping is a standard method for connecting power cables. The reliability and durability of such connections are critical to the continuous operation of production equipment.

The energy sector actively uses crimping at the industrial level. All busbar (loop) connections on high-voltage power lines and substation equipment are made using the crimping method. Special press machines are used for this, since manual crimping is impossible to process large-section wires (for example, 180 mm²).

Crimping is also actively used in the installation of external electrical networks, especially in distribution boxes installed outdoors. The use of different types of terminals for this is not recommended due to the possibility of moisture condensation and subsequent corrosion.

Additionally, the crimping method is used when installing distribution boxes in places inaccessible for periodic inspection and control. The inseparability and reliability of the crimped connections guarantees their long-term operation without the need for maintenance.

Standards and regulatory requirements

Crimping of wires with sleeves is regulated by various normative documents that establish requirements for materials, sleeve design, crimping technology and quality control of connections.

The Electrical Installation Rules (EIR) recognize crimping as one of the acceptable methods of connecting wires, along with soldering, welding, and clamping.

GOST 23469.0-81 "Cable sleeves. General specifications" establishes requirements for cable sleeves of climatic versions U, T, UHL (HL), intended for connection and branching by soldering or crimping of wires and cables for voltage up to 10 kV with copper cores with a cross-section from 0.35 to 300 mm² and with aluminum cores with a cross-section from 2.5 to 300 mm².

According to the standards, sleeves are divided by design into closed ones with one-sided and two-sided filling, as well as open ones for connecting wires and cables with preliminary twisting of cores.

For crimping wires using explosive energy, special standards are used, for example, VSN 34.71.1-83, which determine the technology for preparing and performing work.

Building codes and regulations indicate that for terminating aluminum wire and cable cores, tubular terminals of certain sizes should be used depending on the cross-section of the cores and the rated voltage.

Common Mistakes and How to Avoid Them

When performing crimping, typical errors are often encountered that can significantly reduce the quality and reliability of the connection.

One of the most common mistakes is the wrong choice of sleeve. Using a sleeve made of a different metal than the conductors being connected leads to electrochemical corrosion. For example, a copper core cannot be crimped with an aluminum sleeve and vice versa, since both metals will begin to corrode due to the formation of a galvanic pair.

Another common mistake is insufficient stripping of wires before crimping. The oxide film on the metal surface prevents the formation of a high-quality electrical contact. Therefore, the wires must be thoroughly stripped to a metallic shine.

Incorrect selection of tools is also often the cause of poor-quality crimping. Using pliers or other tools not intended for this purpose can lead to uneven crimping of the sleeve and a subsequent emergency situation.

Another mistake is insufficient or excessive force during crimping. If the force is insufficient, the connection is mechanically unreliable; if it is excessive, the conductors may be damaged and the electrical conductivity may decrease.

Many installers neglect the rule of multi-point crimping with tool rotation. Crimping should be performed at least in two or three points, and in each new crimping the pliers are rotated by 90 degrees to ensure uniform deformation of the sleeve.

To prevent errors, it is recommended to strictly follow the crimping technology, use only specialized tools, correctly select sleeves by material and size, and carefully prepare the wires before connecting.

Comparison with other wire connection methods

In addition to crimping, there are other methods of connecting wires, each with its own advantages and disadvantages.

Welding is comparable in reliability to crimping and also creates a permanent connection. However, it is much more difficult to perform, requires special equipment and highly qualified fitters. In addition, welding requires access to the power grid, which is not always possible in the field.

Soldering is significantly inferior to crimping in mechanical strength and is used mainly for low-current lines. In power circuits, when overloaded or short-circuited, the solder can melt, which will lead to the destruction of the connection. Also, when organizing such a connection, it is necessary to take into account possible mechanical loads, which is required by the PUE rules.

WAGO type terminal blocks provide a detachable connection, which is convenient when modifying electrical wiring. However, they take up a lot of space in distribution boxes, and over time, the quality of the electrical contact in them can deteriorate due to the weakening of the spring mechanism.

Connecting insulating clamps (SIZ) also create a permanent connection and do their job well. Their advantage is the ease of installation without special tools. However, SIZ are usually more expensive than sleeves and are limited by the maximum cross-section of the wires being connected.

Twisting of wires, although the simplest method of connection, is strictly prohibited in electrical wiring. In twisting, electrical contact quickly deteriorates due to oxidation, which leads to increased heat generation and possible fire.

Prospects for the development of technology

Wire crimping technology is constantly being improved; new materials, tools and methods are emerging that improve the quality and reliability of connections.

One of the areas of development is the creation of sleeves with improved anti-corrosion properties, capable of operating in extreme conditions: high humidity, temperature changes, exposure to aggressive environments.

Crimping tools are also being improved. Modern electrohydraulic presses are equipped with electronic systems for controlling the crimping force, which allows for automatic selection of optimal parameters for various types of connections and eliminates the human factor.

Combined sleeves with improved design are emerging, providing a more reliable connection of dissimilar metals without the risk of electrochemical corrosion.

Technologies for quality control of crimping are also being developed. Portable devices for non-destructive testing are being developed, allowing the quality of the connection to be assessed without damaging it, which is especially important when installing critical electrical circuits.

Another promising direction is the creation of “smart” crimping systems capable of automatically selecting the optimal crimping parameters depending on the type of conductors being connected, operating conditions and required connection characteristics.

Crimping wires with sleeves remains one of the most reliable and effective methods of creating electrical connections. A wide range of applications – from household wiring to high-voltage power lines – proves the versatility and efficiency of this technology.

The main advantages of the method – high mechanical strength, reliable electrical contact and resistance to external influences – make crimping the preferred choice for creating critical connections, especially in power circuits with high current loads.

Despite the need for special tools and certain skills, the simplicity of the technology and availability of materials ensure the widespread use of crimping both in professional electrical installation and when performing home electrical work.