Wire connection methods

Contact connections of conductors are very important element electrical circuit, so when executing electrical installation work You must always remember that the reliability of any electrical system is largely determined by the quality of the electrical connections.

All contact connections are subject to certain technical requirements. But first of all, these compounds must be resistant to mechanical factors, be reliable and safe.

With a small contact area, quite significant resistance to the passage of current can arise in the contact zone. The resistance at the point where current passes from one contact surface to another is called transition contact resistance, which is always greater than the resistance of a solid conductor of the same size and shape. During operation, the properties of a contact connection under the influence of various external and internal factors can deteriorate so much that an increase in its contact resistance can cause overheating of the wires and create emergency situation. The transient contact resistance largely depends on the temperature, with an increase in temperature (as a result of the passage of current) the transition resistance of the contact increases. Contact heating is of particular importance due to its influence on the oxidation process of contact surfaces. In this case, the oxidation of the contact surface is more intense, the higher the contact temperature. The appearance of an oxide film, in turn, causes a very strong increase in contact resistance.

This is an element of an electrical circuit where the electrical and mechanical connection of two or more separate conductors is made. At the point where the conductors touch, an electrical contact is formed - a conductive connection through which current flows from one part to another.

Simple overlay or slight twisting of the contact surfaces of the connected conductors does not provide good contact, since due to micro-irregularities, actual contact does not occur over the entire surface of the conductors, but only at a few points, which leads to a significant increase in the transition resistance.

At the point of contact of two conductors, a transition resistance of the electrical contact always arises, the value of which depends on the physical properties of the contacting materials, their condition, the compression force at the point of contact, temperature and the actual area of ​​contact.

From the point of view of the reliability of electrical contact aluminum wire cannot compete with copper. After a few seconds of exposure to air, the pre-cleaned aluminum surface is covered with a thin, hard and refractory oxide film, which has a high electrical resistance, which leads to increased transient resistance and strong heating of the contact zone, resulting in an even greater increase in electrical resistance. Another feature of aluminum is its low yield strength. A tightly tightened connection of aluminum wires weakens over time, which leads to a decrease in the reliability of the contact. In addition, aluminum has poorer conductivity. That is why use in household electrical systems aluminum wires are not only inconvenient, but also dangerous.

Copper oxidizes in air at normal residential temperatures (about 20 °C). The resulting oxide film does not have great strength and is easily destroyed when compressed. Particularly intense oxidation of copper begins at temperatures above 70 °C. The oxide film on the copper surface itself has insignificant resistance and has little effect on the value of the contact resistance.

The condition of the contact surfaces has a decisive influence on the growth of the contact resistance. To obtain a stable and durable contact connection, high-quality cleaning and surface treatment of the connected conductors must be performed. The insulation from the cores is removed to desired length with a specialized tool or knife. Then the exposed parts of the veins are cleaned with emery cloth and treated with acetone or white spirit. The length of the cutting depends on the characteristics of the specific method of connection, branching or termination.

The transient contact resistance decreases significantly with increasing compression force of the two conductors, since the actual contact area depends on it. Thus, to reduce the transition resistance in the connection of two conductors, it is necessary to ensure sufficient compression, but without destructive plastic deformations.

There are several ways to make an electrical connection. The highest quality of them will always be the one that provides the most low value transient contact resistance for as long as possible.

According to the “Rules for Electrical Installations” (clause 2.1.21), connection, branching and terminating of wires and cables must be done by welding, soldering, crimping or clamping (screw, bolt, etc.) in accordance with current instructions. In such connections it is always possible to achieve a consistently low transient contact resistance. In this case, it is necessary to connect the wires in compliance with technology and using appropriate materials and tools.

This is an important and responsible operation. It can be performed different ways: using terminal blocks, soldering and welding, crimping, and often ordinary twisting. All of these methods have certain advantages and disadvantages. It is necessary to select a connection method before starting installation, as this also involves the selection of appropriate materials, tools and equipment.

At connecting wires the same color of neutral, phase and ground wires should be observed. Usually the phase wire is brown or red, the neutral wire is blue, the wire protective grounding- yellow-green.

Very often, electricians have to connect a wire to an existing line. In other words, it is necessary to create a branch of wires. Such connections are made using special branch clamps, terminal blocks and piercing clamps.

In direct contact, copper and aluminum form a galvanic couple, and an electrochemical process occurs at the point of contact, as a result of which the aluminum is destroyed. Therefore, to connect copper and aluminum wires, you need to use special terminal or bolt connections.

Wires connected to various devices often require special ferrules that help ensure reliable contact and reduce contact resistance. Such lugs can be attached to the wire by soldering or crimping.

There are the most various types. For example, for copper stranded conductors, lugs are produced from seamless copper pipe, flattened and drilled for a bolt on one side.

Welding. Connecting wires by welding.

It gives a monolithic and reliable contact, so it is widely used in electrical installation work.

Welding is performed at the ends of pre-stripped and twisted conductors with a carbon electrode using welding machines with a power of about 500 W (for twist cross-sections up to 25 mm2). The current on the welding machine is set from 60 to 120 A depending on the cross-section and number of wires being welded.

Due to the relatively low currents and low (compared to steel) melting point, the process occurs without a large dazzling arc, without deep heating and spattering of the metal, which makes it possible to use safety glasses instead of a mask. At the same time, other security measures may be simplified. After welding is completed and the wire has cooled, the bare end is insulated using electrical tape or heat-shrink tubing. After a little training, welding can be used to make connections quite quickly and efficiently. electrical wires and cables in the power supply system.

When welding, the electrode is brought to the wire being welded until it touches, then withdrawn a short distance (OD-1 mm). The resulting welding arc melts the twisted wires until a characteristic ball is formed. Touching the electrode should be short-term to create desired zone melting without damaging the wire insulation. It is impossible to make a longer arc length, since the welding site turns out to be porous due to oxidation in the air.

Currently, it is convenient to carry out welding work on connecting electrical wires with an inverter welding machine, since it has a small volume and weight, which allows the electrician to work on a stepladder, for example, under the ceiling, hanging a welding machine inverter device on your shoulder. To weld electrical wires, a graphite electrode coated with copper is used.

In a joint obtained by welding, electricity flows through monolithic metal of the same type. Of course, the resistance of such connections turns out to be record low. In addition, this connection has excellent mechanical strength.

Of all the known methods of connecting wires, none of them can be compared with welding in terms of durability and contact conductivity. Even soldering breaks down over time, since the connection contains a third, more fusible and loose metal (solder), and at the border different materials There is always additional contact resistance and destructive chemical reactions are possible.

Soldering. Connecting wires by soldering.

Soldering is a method of joining metals using another, more fusible metal. Compared to welding, soldering is simpler and more affordable. It does not require expensive equipment, is less fire hazardous, and the skills to perform good quality soldering will be required more modest than when making a welded joint. It should be noted that the metal surface in air is usually quickly covered with an oxide film, so it must be cleaned before soldering. But the cleaned surface can quickly oxidize again. To avoid this, apply to the treated areas chemical substances- fluxes that increase the fluidity of molten solder. This makes the soldering stronger.

Soldering is also the best way termination of copper stranded conductors into a ring - the soldered ring is evenly covered with solder. In this case, all wires must completely fit into the monolithic part of the ring, and its diameter must correspond to the diameter of the screw clamp.

The process of soldering wires and cable cores consists of covering the heated ends of the connected wires with molten tin-lead solder, which after hardening provides mechanical strength and high electrical conductivity of the permanent connection. The soldering must be smooth, without pores, dirt, sagging, sharp bulges of solder, or foreign inclusions.

To solder copper conductors of small cross-sections, use solder tubes filled with rosin, or a solution of rosin in alcohol, which is applied to the joint before soldering.

To create a high-quality soldered contact connection, the wire (cable) cores must be thoroughly tinned, and then twisted and crimped. The quality of the soldered contact largely depends on correct twisting.

After soldering, the contact connection is protected by several layers of insulating tape or heat shrink tube. Instead of insulating tape, the soldered contact connection can be protected with an insulating cap (PPE). Before this, it is advisable to coat the finished joint with a moisture-resistant varnish.

Heating of parts and solder is carried out with a special tool called a soldering iron. A prerequisite for creating a reliable connection using soldering is the same temperature of the surfaces being soldered. Great importance for soldering quality, it has a relationship between the temperature of the soldering iron tip and the melting temperature. Naturally, this can only be achieved with the help of a properly selected tool.

Soldering irons vary in design and power. To perform household electrical work, a conventional electric rod soldering iron with a power of 20-40 W is quite sufficient. It is advisable that it be equipped with a temperature regulator (with a temperature sensor) or at least a power regulator.

Experienced electricians often use for soldering original way. In the working rod of a powerful soldering iron (at least 100 W), a hole with a diameter of 6-7 mm and a depth of 25-30 mm is drilled and filled with solder. In a heated state, such a soldering iron is a small tin bath, which allows you to quickly and efficiently solder several multi-core connections. Before soldering, a small amount of rosin is thrown into the bath, which prevents the appearance of an oxide film on the surface of the conductor. The further soldering process involves lowering the twisted connection into such an improvised bath.

One common way to create a contact is to use screw terminal blocks. In them, reliable contact is ensured by tightening the screw or bolt. In this case, it is recommended to connect no more than two conductors to each screw or bolt. When using stranded wires in such connections, the ends of the wires require preliminary tinning or the use of special tips. The advantage of such connections is their reliability and disassembly.

According to their purpose, terminal blocks can be feed-through or connecting.

Designed for connecting wires to each other. They are usually used for switching wires in distribution boxes and distribution boards.

Feed-through terminal blocks are used, as a rule, for connecting various devices (chandeliers, lamps, etc.) to the network, as well as for splicing wires.

When connecting wires with stranded conductors using screw terminal blocks, their ends require preliminary soldering or crimping with special lugs.

When working with aluminum wires, the use of screw terminal blocks is not recommended, since aluminum cores, when tightened with screws, are prone to plastic deformation, which leads to a decrease in the reliability of the connection.

Recently, a very popular device for connecting wires and cable cores has become self-clamping terminal blocks WAGO type. They are designed for connecting wires with a cross-section of up to 2.5 mm2 and are designed for an operating current of up to 24 A, which allows you to connect a load of up to 5 kW to the wires connected by them. In such terminal blocks you can connect up to eight wires, which significantly speeds up the installation of wiring in general. True, compared to twisting, they take up more space in soldered boxes, which is not always convenient.

The screwless terminal block is fundamentally different in that its installation does not require any tools or skills. The wire, stripped to a certain length, is inserted into place with little effort and securely pressed by a spring. The design of a screwless terminal connection was developed by the German company WAGO back in 1951. There are other manufacturers of this type of electrical products.

In spring-loaded self-clamping terminal blocks, as a rule, the effective contacting surface area is too small. At high currents, this leads to heating and release of the springs, resulting in a loss of their elasticity. Therefore, such devices should be used only on connections that are not subject to heavy loads.

WAGO produces terminal blocks both for installation on a DIN rail and for fastening with screws to a flat surface, but when mounted as part of home wiring construction terminal blocks are used. These terminal blocks are available in three types: for distribution boxes, for lamp fittings and universal.

WAGO terminal blocks for distribution boxes they allow connecting from one to eight conductors with a cross-section of 1.0-2.5 mm2 or three conductors with a cross-section of 2.5-4.0 mm2. And terminal blocks for lamps connect 2-3 conductors with a cross section of 0.5-2.5 mm2.

The technology for connecting wires using self-clamping terminal blocks is very simple and does not require special tools or special skills.

There are also terminal blocks in which the conductor is fixed using a lever. Such devices allow you to achieve good pressure, reliable contact and are easy to disassemble.

One of the connecting products popular among electrical installers is. This clamp is a plastic case, inside of which there is an anodized conical spring. To connect the wires, they are stripped to a length of about 10-15 mm and folded into a common bundle. Then the PPE is screwed onto it, rotating clockwise until it stops. In this case, the spring compresses the wires, creating the necessary contact. Of course, all this happens only when the PPE cap is selected correctly according to its rating. Using such a clamp, it is possible to connect several single wires with a total area of ​​2.5-20 mm2. Naturally, the caps in these cases are of different sizes.

Depending on the size, PPE has specific numbers and is selected according to the total cross-sectional area of ​​the strands being twisted, which is always indicated on the packaging. When choosing PPE caps, you should focus not only on their number, but also on the total cross-section of wires for which they are designed. The color of the product has no practical meaning, but can be used to mark phase and neutral conductors and ground wires.

PPE clamps significantly speed up installation, and due to the insulated housing, they do not require additional insulation. True, their connection quality is somewhat lower than that of screw terminal blocks. Therefore, other things being equal, preference should still be given to the latter.

Twisting. Twisted connection of wires.

Twisting bare wires as a connection method is not included in the “Electrical Installation Rules” (PUE). But despite this, many experienced electricians consider a correctly performed twist as a completely reliable and high-quality connection, arguing that the transition resistance in it is practically no different from the resistance in the whole conductor. Be that as it may, good twisting can be considered one of the stages of connecting wires by soldering, welding or PPE caps. Therefore, high-quality twisting is the key to the reliability of all electrical wiring.

If the wires are connected according to the “as it happens” principle, a large transition resistance may arise at the point of their contact with all the negative consequences.

Depending on the type of connection, twisting can be performed in several ways, which, with a small transition resistance, can provide a completely reliable connection.

First, the insulation is carefully removed without damaging the wire core. Sections of cores exposed to a length of at least 3-4 cm are treated with acetone or white spirit, sanded with sandpaper to a metallic shine and tightly twisted with pliers.

Crimping method Widely used to make reliable connections in junction boxes. In this case, the ends of the wires are stripped, combined into appropriate bundles and pressed. The connection after crimping is protected with electrical tape or heat shrink tubing. It is one-piece and does not require maintenance.

Crimping It is considered one of the most reliable methods of connecting wires. Such connections are made using sleeves by continuous compression or local pressing with special tools (press jaws), into which replaceable dies and punches are inserted. In this case, the wall of the sleeve is pressed (or compressed) into the cable cores to form a reliable electrical contact. Crimping can be done by local pressing or continuous compression. Continuous crimping is usually done in the shape of a hexagon.

Before crimping, it is recommended to treat copper wires with a thick lubricant containing technical petroleum jelly. This lubrication reduces friction and reduces the risk of damage to the core. Non-conducting lubricant does not increase the contact resistance of the connection, since if the technology is followed, the lubricant is completely displaced from the contact point, remaining only in the voids.

For crimping, manual press pliers are most often used. In the most common case, the working parts of these tools are dies and punches. In general, the punch is a movable element that produces local indentation on the sleeve, and the matrix is ​​a shaped fixed bracket that perceives the pressure of the sleeve. Dies and punches can be replaceable or adjustable (designed for different cross-sections).

When installing ordinary home wiring, small crimping pliers with shaped jaws are usually used.

As a sleeve for crimping, you can, of course, use any copper tube, but it is better to use special sleeves made of electrical copper, the length of which corresponds to the conditions for reliable connection.

When crimping, the wires can be inserted into the sleeve either from opposite sides until mutual contact is strictly in the middle, or from one side. But in any case, the total cross-section of the wires must correspond to the inner diameter of the sleeve.

K category: Electricity in the country

Termination and connection of wires and cables

The reliability of the electrical installation largely depends on the quality connection of wires and cables. The most difficult connection aluminum conductors wires and cables. The fact is that aluminum, being a good conductor, has a number of unfavorable properties that must be taken into account when making contact connections. These include: the rapid formation of an oxide film in air, the melting point of which is about 200 ° C (the melting point of aluminum itself is approximately 650 ° C); creep under pressure; negative potential in relation to copper and steel; high heat capacity.

The aluminum oxide film has high electrical resistance and therefore impairs electrical contact. Creep under pressure causes aluminum to partially flow out from under the joint, weakening the electrical contact. Negative potential in relation to copper, steel, zinc leads to the creation of a galvanic couple when connecting aluminum with these metals, in which aluminum is gradually destroyed. If the wire cores are connected poorly, overheating of the insulation or burnout of the wires themselves may occur during welding and soldering.

But despite the above unfavorable properties aluminum, simple and fairly reliable methods of connecting aluminum cores are currently used.

Crimping using GAO sleeves is one of the best methods that should be used for connecting and branching aluminum single-wire wires with a cross-section of 2.5-10 mm2.

If the total cross-section of the cores is less internal diameter sleeves, then an additional core is inserted into the sleeve. The insulation is removed from the ends of the wires, the bare areas of the conductors are cleaned under a layer of technical petroleum jelly or quartz-vaseline paste, the stripped conductors are wiped and lubricated with clean quartz-vaseline paste. Next, clean the inner surface of the sleeve to a metallic shine with a brush lubricated with technical petroleum jelly, wipe the sleeve outside and inside with a cloth moistened with gasoline. After wiping, the inner surface of the sleeve is immediately lubricated with quartz vaseline paste. These operations are performed if the quartz vaseline paste was not applied at the factory. Then the prepared conductors are installed in the sleeve and its filling is checked. The voids are filled with sections of veins lubricated with quartz-vaseline paste. A one-sided sleeve is pressed with one pressing, and a double-sided one with two pressings using press pliers PK.-3, PK-2m or PK-1m.

Connecting aluminum conductors with a total cross-section of up to 10 mm2 in clamps with two carbon electrodes is the recommended method. To make the connection, use pliers to twist the prepared ends of the wires, avoiding twisting of the wires in the insulation. Lubricate the ends of the wires thin layer diluted flux by YOU, direct the prepared ends of the cores down. The ends of the carbon electrodes are short-circuited and heated. Next, turn off the pliers, press the hot electrodes to the ends of the wires and hold them in this position until a ball forms on the wires. Remains of flux and slag are removed with a cardboard brush, and the joint is washed with gasoline and coated with moisture-resistant varnish.

The connection of aluminum conductors with a total cross-section of 2.5-10 mm2 by double twisting with a groove is carried out in cases where there are no conditions for the use of crimping or welding. To perform soldering, the ends of the wires are prepared - areas for stripping are determined at the ends of the wires, the insulation is removed and the wires are cleaned to a metallic shine with a carded tape brush. The wires are twisted as shown in Fig. 3, a. After twisting, the wires should be even and pressed against each other. Burner flame or gasoline blowtorch(Fig. 3.6) heat the twisting of the wires until the solder begins to melt. Insert a stick of solder, grade A or grade TsO-12, into the flame and rub the groove with it until it is completely tinned and filled with solder. Next, the trench is rotated 180° and operations are performed to fill it with solder.

Rice. 1. Crimping of single-wire aluminum cores in GAO sleeves: a - choice of sleeve; b- removal of insulation from the ends of the cores; c, d - cleaning and lubrication inner surface sleeves; d - installation of cores into the sleeve; e - crimping

Soldering of cores can also be done with a soldering iron. The joint is coated with moisture-resistant varnish and insulated (Fig. 3, c). To make one connection of single-wire conductors with a cross-section of 2.5-4 mm2, approximately 1 g of solder and 5.5 g of gasoline are consumed. Soldering duration is 25 s.

Connecting and branching copper conductors with a cross-section of up to 10 mm2 using soldered twisting is one of the best methods. To connect the wires, the insulation is removed from the ends of the wires, the wires are stripped to a metallic shine and twisted with pliers so that the turns fit tightly together. The twist is coated with a solution of rosin or soldering fat and soldered using a soldering iron, blowtorch or gas burner. For soldering, soft tin-lead solders of the GYUS-40 or POS-61 grade are used.

Rice. 2. Connection of aluminum conductors in clamps with two carbon electrodes: a - stripping of insulation; b - stripping and twisting of cores; c - flux coating; d and d - twist welding; e - processing of welding spots; 1 - carbon electrode; 2 - twisting of aluminum cores; 3 - two-electrode clamps; 4 - step-down transformer

Termination of copper stranded conductors with a cross-section of up to 2.5 mm2 in ring lugs in accordance with GOST 9688-82 is one of the best ways which should be applied. Remove the insulation at a distance of 25-30 mm from the end of the core using a special tool - a lineman's knife, loosen the twisted wires of the core and strip the cores to a metallic shine. Twist the stripped wires and twist the end of the core into a ring clockwise.

Rice. 3. Connection of single-wire aluminum conductors by double twist soldering with a groove

Depending on the cross-section of the conductive core and the contact screw, an end tip is selected, onto the cylindrical part of which the core is placed.

The tip with the core is put on the rod of the punch installed in the PK-2m press jaws so that the section of the core between the tip and the insulation is placed in the groove of the punch. By pressing the handles of the press pliers until the ends of the matrix and punch stop, crimping is carried out. Unclench the pliers and remove the finished connection.

Bending the end of a stranded strand into a half-ring is another recommended termination method. The end of the core is formed into a ring as described above, coated with a solution of rosin in alcohol, immersed in GYUS-40 solder at G-2 s or soldered using a soldering iron.

It is recommended to connect aluminum-copper cores using GAO sleeves using the technology adopted for connecting aluminum cores. Welding of aluminum-copper conductors by known methods does not provide the required quality of contact connections. A satisfactory connection can be obtained by crimping without the use of sleeves using modernized KSP press tongs. Technologically, the connection is made as follows: the wires are twisted in one of the holes of the press pliers, then they are upset, the connection is released and the flash is removed. When performing one upsetting, the mechanical strength of the connection may be insufficient: individual wires of the core may move. In this case, the sedimentation is repeated 2-3 times.

Connecting elements electrical network.

When connecting elements of the electrical network, it should be remembered that: – the zero grounding conductor should not have breaks anywhere, even if only short-term; – a single-phase switch must be installed in phase wire. This requirement does not apply to portable electrical receivers and lamps connected to the network with a plug connection.

When installing after laying the wires, phase and neutral wires marked with any conventional signs(for example, they strip the insulation at the end of the wire or bend the wires on the wire of the same name).

Wires of the same name are determined using an auxiliary wire, to which a flashlight battery with a light bulb is connected. If the light bulb is on, it means it is connected to different ends of the same wire.

MINISTRY OF AGRICULTURE AND FOOD

Republic of Belarus Main Directorate of Education, Science and Personnel

EDUCATIONAL INSTITUTION

"BUDA-KOSHELEVSKY STATE AGRICULTURAL-TECHNICAL COLLEGE"

Discipline "Technology of electrical installation work"

Speciality:

2-74 06 31-01 “Energy supply for agricultural production (electric power).”

Laboratory work No. 3

Subject:

Studying the quality of connections of wires and cables, performed in various ways.

Goal of the work:

Study methods of making non-separable and collapsible contact connections. Gain practical skills in making contact connections by soldering, welding, and crimping.

Completed by: student

3 Courses, 55 es groups

Polyakov A.Yu.

Checked by: teacher

Lashkevich A.V.

1. Topic and purpose of the lesson.

2. Brief theoretical information.

3.Draw drawings.

METHODOLOGICAL INSTRUCTIONS

Methods for connecting wires and cables

Electrical connections are made by welding, soldering, crimping, and creating dismountable contact connections.

Welding. Welding is used for terminating and connecting aluminum conductors of wires and cables of all sections, as well as for connecting aluminum conductors with copper conductors with a cross-section of no more than 10 mm 2. There are three welding methods; electric welding by contact heating, thermite and gas.

When terminating and connecting aluminum cores by welding, VAMI flux is used. The flux is designed to remove the oxide film from the surface of aluminum conductors and to protect the surface from oxidation. VAMI flux is a mixture of three components: potassium chloride (50%), sodium chloride (30%), cryolite (20%). The melting point of the flux is 630 °C. The chemical industry produces flux in the form of a powder, packaged in hermetically sealed jars. Before use, flux powder is diluted with water to the consistency of thick sour cream (100 parts of flux to 30...40 parts of water by weight). Before welding, the flux is applied with a hair brush in a thin layer to the surface of the aluminum conductors; applying flux in a thick layer does not improve the quality of the connection.

Electric welding by contact heating is the most common type of welding used for terminating and joining aluminum wires and cables. It is performed: using pliers with two carbon electrodes (Fig. 1); using a clip (Fig. 2).

Rice. 1– Connection of aluminumRice. 2– Connection of aluminum

lived in tongs with two electrodes: lived by electric welding with tongs with

1-carbon electrode; 2-twisting using a clip:

aluminum conductors; 1-clip made of steel strip;

3-two-electrode clamp 2-carbon electrodes;

3-two-electrode clamp

Gas welding is used for terminating, connecting and branching aluminum conductors. To connect single-wire conductors with a total cross-section of up to 20 mm 2 - propane-air welding and only for termination - oxygen-acetylene welding. Termination, connection and branching of copper conductors by gas welding are not allowed.

Propane-oxygen welding in steel forms they are used for terminating cores with a cross section of 300... 1500 mm 2 and are performed using AD31T1 hard alloy plates and LS tips.

For conductors with a cross-section of 16...240 mm" rod termination is used by fusion into a monolith with the addition of alloying additives from aluminum alloys. The connection of conductors with a cross-section of 16...1500 mm 2 can be made end-to-end, and conductors with a total cross-section of up to 400 mm 2 - at the ends in a common monolithic rod.

Thermite welding provides high quality electrical contact. It is carried out using a thermite cartridge, which consists of a muffle (thermite mass) and a steel cylindrical mold-mold. When the thermite mass is burned inside the mold, a temperature is established that allows aluminum to be successfully welded.

Thermite welding is used for connecting, terminating and branching aluminum cores of wires and cables. For welding at the ends of stranded aluminum conductors with a total cross-section of up to 240 mm 2, thermite cartridges of the PAT brand are used, for welding single-wire conductors of small sections - the PATO brand, for butt-connected conductors of wires and cables with a cross-section of 16...800 mm - thermite cartridges of the PA brand.

When connecting and terminating, the ends of the cores are inserted into the mold of the thermite cartridge.

Soldering is a type of metalworking used to form a permanent joint using a molten intermediate metal or alloy called solder.

Tinning - this is coating the metal with a thin layer of solder to protect it from oxidation, as well as at the junction of the wires for good contact.

Fluxes are called auxiliary materials used in soldering. They serve to dissolve and remove oxide films from the surface of the metals being joined and from the melt, as well as to form a durable, airtight film on its surface. Therefore, fluxes have a density and melting point lower than the solder used (Table 1).

Soldering aluminum difficult due to its easy oxidation with the formation of a strong oxide film on the surface. It is usually removed directly during soldering mechanically, by rubbing it with a special metal brush or directly with a solder stick. The oxide film is removed under the solder layer and the latter is firmly connected to the metal surface. Aluminum conductors are soldered using solders A, TsO-12, TsA-15.

TsA-15 solder is characterized by high mechanical strength and resistance to corrosion. When using it, no special measures are required to protect the soldering area from corrosion. However, it has the disadvantage of a high melting point, which limits its use in electrical installation practice due to the risk of overheating of the core insulation during soldering.

Solder TsO-12 has a lower melting point than TsA-15, but does not have sufficient anti-corrosion resistance. It is used for soldering aluminum cable cores inside couplings, the hermetic seal of which prevents moisture and air from entering the soldering area.

Solder A has a low melting point and resists corrosion better than TsO-12 solder. However, soldering areas must be covered with moisture-resistant varnish and carefully insulated.

Copper conductors are soldered using soft tin-lead solders POS-30, POS-40, etc. using fluxes.

When soldering, a soldering iron (for cores with a cross-section of up to 10 mm2), a gasoline blowtorch with a capacity of 0.5... 1 liter, or a special set of tools with cylinders filled with propane-butane are used as a heat source.

Crimping

Crimping - connection of wire cores by local pressing or continuous and combined crimping.

Connecting, branching and terminating copper and aluminum conductors by crimping is widespread in electrical installation practice. When crimping, a wire or cable core is inserted into the tubular part of the tip or a special sleeve and compressed using a matrix and a punch. The contact pressure created between the sleeve and the core ensures a reliable electrical connection.

When crimping by local pressing with punch teeth in one or several places, high pressure is created in one place and the best electrical contact is achieved,

When crimping by continuous crimping, high pressure and, consequently, good electrical contact are created throughout the entire crimping period.

Combined compression makes it possible to improve the electrical contact between the core and tubular part of the tip or sleeve due to the fact that under conditions of continuous compression, additional high pressure is created at the point where the chanson tooth is pressed in by the matrix and the punch. Various tools and mechanisms are used for crimping.

When choosing a crimping method (local pressing, continuous or combined crimping), it is enough to master the techniques for performing one of them, because, despite the external differences when performing crimping using these methods, most of the operations are the same. Crimping with continuous or combined crimping requires the use of powerful presses with great force. For crimping by local indentation, you can use all kinds of pliers. In addition, the local pressing method is most widely used when performing electrical installation work.

When working with the tool, you must observe general rules safety precautions, as well as the rules given in the operating instructions for presses, tongs and other tools.

The reliability of the contact connection in all cases is quite high if the area of ​​application is correctly determined, the tip or sleeve and working tools are accurately selected, the surfaces are carefully prepared and the crimping is carried out correctly.

Termination

Termination- design of the ends of wires or cables for subsequent connection.

To terminate aluminum cores (with a cross-section from 16 to 240 mm"), wires with voltages up to 2 kV and cables up to 35 kV, tubular lugs should be used; for cores (with a cross-section of 2.5 mm2) of wires with voltages up to 2 kV and cables up to 1 kV, ring lugs should be used tips (pistons).

Tools for processing, connecting and terminating wires and cables.

Tools for processing, connecting and terminating wires and cables. Processing, connecting and terminating wires and cables are technological steps that include cutting the conductor, removing insulation from it, and making a ring clamp. The work is performed in the installation area or in the oil extraction plant using manual or mechanized tools and mechanisms.

To cut (cut) wires and cables, IC sector scissors are used (Fig. 3, a), in which the force applied to the handles of two levers is transferred to the cutting force of the sector knives through a ratchet mechanism. Sector scissors cut wires and cables with aluminum conductors with a cross section of 3X240 mm 2 and copper conductors with a cross section of 3X150 mm 2

The insulation from the wire strands is removed with tools that contain a driving mechanism that transmits forces from two handles (instead of the previously used three) to cutting knives moving towards them, and a mechanism that removes the notched insulation. Knives have cutting edges in the form of two semicircles, calibrated according to the diameter of the core and allowing for adjustment. With the MB-1M tool you can remove rubber, plastic and cotton insulation from the ends of wires and cable cores of various brands and sections (0.75-6 mm2).

When terminating and joining aluminum and copper wires With a core cross section of 16-240 mm 2, crimping is widely used. Unified sets of tools are produced: NIOS (for crimping aluminum conductors) and NYOM (for crimping copper conductors), as well as unified manual presses with mechanical, hydraulic or electric drive.

In electrical installation production, the most widely used are the electrically conductive press PG-20, the manual hydraulic press PGR-20 Ml and the manual mechanical press RMP-7. Crimping ferrules and sleeves on conductors with a cross-section of up to 35 mm 2 is effectively performed using mechanical-type press jaws with a lever mechanism for transmitting force. Press pliers PK-3 (Fig. 3, b) are designed for crimping aluminum cores in sleeves GAO-4, GAO-5, GAO-b, copper cores with a cross-section of 4-b mm 2 in tips of the T series and sleeves of the 1M series, a also for terminating copper conductors with a cross-section of 1.5 and 2.5 mm 2 in cable end lugs (pistons) of the P series. Press flares PK-4 (Fig. 3, c) are intended for crimping aluminum lugs and connecting sleeves on wires and cables core cross-section 16-35 mm", as well as sleeves GAO-5, GAO-6, GAO-8.

In addition to the means of mechanization of electrical installation work described above, there are others (metalwork tools, hand mandrels, welding equipment, a device for bending pipes, tightening wires into pipes).

Figure 3 – Tool for processing and terminating wires and cables:

a - sector scissors type NS-3; b - press tongs PK-3; c - press jaws PK-4.

Demountable contact connections.

Dismountable contact connections are called:

Connecting wires and cables directly to the terminals of electrical equipment (electric motors, control and protection equipment, etc.);

Connecting busbars and branches from them using bolts;

Making branches of wires and cables from main electrical lines without breaking them:

Connecting wires using clamps.

Power electrical equipment, as a rule, has flat, pin and socket contact terminals (Fig. 3).

These terminals allow for detachable connection of wires and cables with electrical equipment. The terminals of the contact terminals of electrical automation, control, alarm and protection devices can also be petal, pin and grooved (Fig. 4). Only copper wires and cables are connected to them by soldering.

Figure 4 – Electrical equipment contact terminals: a-female; b-pin;

in-flat; g,d-petal; g-grooved; z-pin.

In switchgears, power circuits, secondary circuits, as well as for connecting conductors to installation products, transition contact clamps are used (branch clamps, chandelier clamps, terminal blocks made of stacked or non-stacked clamps) (Fig. 5).

Figure 5 – Mechanical clamps: a, b, c – transition contact;

g, e, f, g – branch; h – screw.

The design and main dimensions of flat and pin terminals of electrical equipment are regulated by GOST 21242-75. Electrical equipment terminals are usually made of copper, aluminum and their alloys. At currents up to 40 A they can be made of steel. The copper and steel terminals are metal-coated with tin, zinc-tin alloy, cadmium and nickel.

The immediate installation of contact connections in electrical installations is preceded by the termination of wire and cable cores. Termination of cores with a cross-section of up to 10 mm 2 can be done in the form of a pestle, ring, tip, using soldering or crimping (Fig. 6).

Figure 6– Types of termination of conductors of wires and cables: a - in the form of a pestle;

b - in the form of a ring; c - block tip; g - limiting

puck; d - star washer; e – tip.

It is recommended to remove insulation from the ends of cores with a cross-section of up to 4 mm 2 using pliers KSI, KY-1, etc. When removing insulation with a knife, the latter is directed at an angle of 10.., 15° to the surface of the wire so that, cutting off the insulation, it slides along the surface veins without damaging it.

Connecting aluminum conductors to electrical equipment terminals

The connection of single-wire aluminum conductors with a cross-section of up to 10 mm 2 to the flat terminals of electrical equipment is carried out after stripping the conductor under a layer of neutral lubricant (vaseline, CIATIM - 221 or quartz-vaseline paste). After stripping, remove the dirty grease, replace it with clean grease, and bend the end of the wire into a ring. When connecting to the terminal, install an asterisk washer and a spring washer (rns. 7).

Figure 7– Connecting an aluminum conductor to a flat terminal

electrical apparatus:

1-screwdriver; 2-screw; 3-spring washer; 4-star washer;

5-aluminum cores; 6-pin output.

Single-wire aluminum conductors with a cross-section of 2.5 mm, pre-terminated with a type P ring lug, are connected to the pin terminals by tightening between two nuts with the installation of a washer and a spring washer. Single-wire aluminum conductors with a cross-section of 2.5...10 mm 2, not terminated with a ferrule, are first cleaned to a metallic shine under a layer of neutral lubricant and the conductor is formed into a ring. Then tighten on the pin terminal between the two nuts with the installation of an asterisk washer and a spring washer.

It must be remembered that connecting aluminum conductors to pin terminals and terminals of electrical equipment installed in damp rooms, in aggressive environments, or outdoor installations is not allowed.

In such conditions, the connection of aluminum conductors is allowed only after terminating them with copper-aluminum pin tips.

Connecting copper wires and cables to terminals

electrical equipment.

The connection of single-wire copper conductors with a cross-section of up to 10 mm 2 to flat copper terminals is carried out after stripping the conductor to a metallic shine and then forming it into a ring. A washer and a spring washer are installed between the screw head and the core (Fig. 6).

The connection of copper stranded conductors with a cross-section of up to 10 mm 2 to flat copper terminals is carried out after terminating the conductors with a tip or forming the conductor into a ring with soldering. In this case, only a spring washer is installed between the screw head and the tip.

Single-wire copper cores of wires and cables are connected directly to the socket terminals. Stranded copper conductors, regardless of cross-section, are connected only after they are terminated with pin tips. It is allowed to connect a stranded core after tinning the end of the core into a monolithic rod. Single-wire copper conductors with a cross-section of up to 10 mm 2 are connected to the pin terminals after stripping them to a metallic shine and forming them into a ring. The veins are cleaned of dirt and grease with a solvent. A nut is screwed onto the pin terminal, a ring of copper conductor is put on, after which a washer and a spring washer are installed on the pin terminal and the pin terminal nuts are tightened with a wrench. Stranded copper conductors with a cross-section of up to 10 mm 2 must be terminated with lugs or formed into a ring with soldering. In this case, a washer and a spring washer are also installed when connecting.

1. General information about connection and termination of wires and cables

2. Screw connections

3. Pressure testing

1. General information about connecting and terminating conductive cores of wires and cables

Connecting and terminating the conductive cores of wires and cables are very important operations, the correct execution of which largely determines the reliability of electrical installations. Contact connections are divided into detachable and permanent. The former are performed using screws, bolts, wedges and clamps, the latter are carried out by welding, soldering and crimping.

For reliable operation the contact connection must:

Have low electrical resistance, not exceeding the resistance of an entire section of the same length. (Increased contact resistance leads to increased local heating, which can cause destruction of the connection. According to the standards, short-term heating of the conductors is allowed at short circuit up to 150 °C with rubber and plastic insulation and up to 200 °C with paper insulation. It is clear that the contact connection must withstand the same temperatures and, in addition, operate reliably during repeated heating and cooling.);

Have high mechanical strength (especially if the connection must withstand significant mechanical forces - connecting tires, wires air lines and etc.);

Be resistant to the effects of caustic vapors and gases, changes in temperature and humidity, possible vibrations and shocks that may occur during operation of the equipment.

In electrical installation practice, copper and aluminum conductive parts are used. When installing connections, pairs of “copper - copper”, “aluminum - aluminum” and “copper - aluminum” are possible. In copper, the oxide film forms slowly, has little effect on the quality of the contact connection and is easily removed. Therefore, the connection of copper conductive parts has the best electrical and mechanical properties. Aluminum also oxidizes in air, but its oxide film forms very quickly, has great hardness and high electrical resistance. In addition, the melting point of this film is about 2000 ° C, so it prevents soldering and welding of aluminum wires using conventional methods.

In the connection of copper with aluminum, a galvanic couple is formed, as a result of which the connection is quickly destroyed by electrochemical corrosion.

2. The main type of contact connection of copper and aluminum conductors of small cross-section to electric machines, devices and devices - screw connection. It is used for wires with a cross section of up to 10 mm2.

To connect copper conductors of small cross-sections, they are bent in the form of a ring, which in the case of a multi-wire conductor is soldered. Screw connections of aluminum conductors make them somewhat more difficult. The fact is that aluminum under pressure begins to “flow” into an area with lower pressure. Therefore, if aluminum connection over-tighten the screw, then over time the contact connection will weaken, as some of the metal will “leak out” from under the washer. This process occurs especially quickly when the connection is periodically heated and cooled. To prevent this phenomenon screw clamp must have a device that protects the aluminum ring from unwinding and compensates for loosening of contact due to the fluidity of aluminum.

To lock the ring, use a star washer or a rectangular washer with sides, and spring washers are used to compensate the pressure. Before tightening the screw, the contact surfaces are cleaned to a shine and lubricated with quartz vaseline paste.

3. When connecting by crimping, the ends of the connected wires are inserted into the connecting sleeve (a piece of tube made of pure copper or aluminum) and compressed with a special tool. The cleanliness of the contact surfaces is of great importance for the quality of the connection, therefore, with any method of crimping, dirt, insulation residues and oxide films must be removed from the cores and sleeves. The oxide film is removed from copper wires during the crimping process, when the surface of the metal stretches and “flows,” so no special treatment other than stripping is required for copper wires. As for aluminum, to destroy the durable film of its oxide, a paste consisting of petroleum jelly with the addition of hard grains is applied to the cleaned contact surfaces quartz sand or zinc oxide. When crimping, solid particles destroy the film, and Vaseline prevents re-oxidation of the contacts.

Crimping of aluminum wires with a cross-section of up to 10 mm2 is carried out in GAO-type sleeves (outer diameter up to 9 mm) using PK-2M pressing pliers (Fig. 4.33). They have handles with a lock 5 that limits the degree of indentation, one of which is connected to a thrust bracket 3, and the second to a pusher 4. A matrix 2 is fixed to the bracket, and a punch 2 with a tooth is attached to the pusher.

Rice. 4.35. Crimping of wires in GAO sleeves: Fig. 4.33. Pressing pliers PK-2M

a - in a shortened sleeve, b - in an elongated sleeve, c - installation of the sleeve in the press, d - sleeve after crimping, d - insulation of the sleeve

Due to the long length of the handles, the PK-1M press jaw (Fig. 4.34) creates pressure sufficient for crimping cartridges with a diameter of up to 14 mm. In GKM hydraulic assembly pliers, the working movement of the pusher with the punch occurs due to the pressure in the hydraulic cylinder, which occurs when the handle is pressed.

Technological process crimping is shown in Fig. 4.35. Preparing aluminum wires for connection involves stripping them and coating them with paste. After this, a shortened GAO sleeve is put on the ends of the wires (for one-sided crimping, Fig. 4.35, a) or an extended sleeve of the same brand (for double-sided crimping, Fig. 4.35, b) and make one or two indentations with a press or pliers (Fig. 4.35 , c, d). The punch is pressed into the sleeve until the clamp-limiter is activated or until the punch touches the matrix (if the press jaws do not have a clamp). The pressed contact connection is cleaned of paste residues and insulated with polyethylene caps or insulating tape (Fig. 4.35, e).

For crimping aluminum wires and cable cores with a cross-section of 16...240 mm2, GA type sleeves are used. Presses are used as crimping tools to create large pressing forces. In Fig. 4.36 shows a manual mechanical press RMP-7M and a manual Hydraulic Press RGP-7M. The first of them works on the same principle as press tongs, the operation of the second is similar to the action of hydraulic tongs GKM. The pressing force of these pliers is up to 69 kN (7 t),

Rice. 4.36. Tool for crimping: a-mechanical press RMP-7M, b-hydraulic press RGP-7M

Requirements for the quality of connections, branches and terminations. According to the PUE, the following requirements are imposed on the quality of connections, branches and terminations:

1. Connection, branching and terminating of wires and cables must be done using crimping, welding, soldering or clamps (screw, bolt, etc.).
2. At the points of connection, branching and connection of wire or cable cores, a supply of wire (cable) must be provided to ensure the possibility of reconnecting the branch or connection.
3. Connections and branches of wires and cables must be accessible for inspection and repair.
4. At junctions and branches, wires and cables should not experience mechanical tension.
5. Places of connection and branching of conductors of wires and cables, as well as connecting and branch clamps, etc. must have insulation equivalent to the insulation of conductors of entire sections of these wires and cables.
6. Connection and branching of wires and cables, with the exception of wires laid on insulating supports, must be carried out in junction and branch boxes, in insulating housings of connecting and branch clamps, in special niches building structures, inside the housings of electrical installation products, devices and machines. When laying on insulating supports, the connection or branch of the wires should be made directly at the insulator, the face or on them, as well as on the roller.

Connection methods. Let's look at some ways to connect wire cores and electrical cables.

• Terminal clamps. Available with a clamping bar for connection stranded wires, and without a clamping strip, for single-core. The design of the terminal blocks makes it possible not to use additional insulation at the connection point.
• Yoke clamp. It differs from conventional terminal clamps in that the clamping strip has notches that cut the oxide layer on the wire core, increasing the contact area and the quality of the connection. In addition, the design of the body of this clamp prevents spontaneous loosening of the clamping screw.
• Piercing clamp. The peculiarity of the clamp is that when connecting wires, it is not necessary to remove the insulation from the latter. The clamp consists of a plastic body and an W-shaped contact plate, which, after mounting the clamp, moves the wire insulation apart and provides electrical contact between the connected wires.
• Spring clamp. It is the most in a simple way wire connections. All you need to do is strip the core of insulation and insert it into the clamp, where it is securely fixed using a special spring mechanism. One of the advantages of these clamps is the ability to connect wires of different diameters, both copper and aluminum; they do not contact each other, which eliminates electrocorrosion. In addition, the gel filling the internal volume destroys the oxide film on aluminum and protects it from corrosion.

Branch. To make a branch, the same methods are used as for connecting wires and cables.

In addition to the types described above, branch clamps of the “nut” type are often used as clamps, consisting of two steel plates with grooves for conductors, compressed by four screws, located in a plastic case. Between them there is another flat plate, which eliminates direct contact between the cores when copper and aluminum wires are connected.

Drawing. The branch clamp is “walnut”.