The most important task when connecting any electrical contacts is to ensure their minimum resistance. With poor contact, the resistance between copper wires increases significantly, resulting in heating of the cable. There are many ways to connect contacts, but the most reliable and efficient is considered to be welding of copper wire. This technology allows you to seamlessly connect all the wires of the wire, thereby achieving the lowest possible electrical resistance. As a result, the heating of the wires is eliminated, therefore, the fire safety level is significantly increased.
Wire Connection Methods
Copper is the main material of conductors. Due to the physicochemical properties of this material (high ductility, lack of elasticity), working with it has its own characteristics. Electrical installation rules state that the connection, branching and termination of cable and wire cores can be performed by soldering, welding, crimping or clamping (bolt, screw, etc.). Each of them has its own characteristics, which will be discussed below.
Wire connection by twisting
Simple twisting of wires is prohibited by the PUE, since this is the most inefficient, short-lived and fire hazardous connection. Despite this, home craftsmen never stop using this method, even though the consequences of such “needlework” can be the most fluent.
The twisting of wires has one important drawback: over time, copper connections become deformed and weaken, eventually finally collapsing due to high transition resistance.
It should be remembered that the method of twisting can be used only in exceptional cases, if it is urgent to restore power supply, and other methods in a specific situation are not available. It is very important to take care of the quality, safety and reliability of the connection.
It is strictly forbidden:
- Connect wires made of different materials (aluminum and copper);
- Connect a single-core copper wire to a multi-core wire.
The twisting process is as follows:
- Clean the wires from insulation at a distance of 6-8 cm from the edge;
- Lay one wire crosswise across the other and twist as tight as possible. If the cross-section of the copper wire is more than 1 square. mm, this operation is performed using pliers.
- Bite off the remaining ends of the wires with pliers.
- Insulate the twist using special insulating materials (PVC or heat-shrink tubing, caps) or several layers of insulating tape. Insulation must necessarily capture the insulating layer of the wires.
This method is the process of connecting the wires by crimping them with a special tubular sleeve or tip. These devices are used if the cross-section of the copper wire is 2.5-240 square meters. mm The indisputable advantages of crimping technology are the speed and accuracy of work, as well as the subsequent durability and safety of the joints.
For crimping, a special tool is used - mechanical, hydraulic or electric pincers
or professional crimping presses. The selection of sleeves is carried out taking into account the cross section and the number of connected wires.
After removing the insulation and stripping the cores, quartz-petroleum jelly paste is applied to them, a sleeve is put on and crimping is performed. The pressed sleeves isolate.
Crimps and terminal blocks
The use of various crimps and terminal blocks is quite widely practiced when connecting electrical outlets, switches, lighting devices, as well as when installing switchboards. These devices allow you to neatly and quickly connect a single-core copper wire, however, you can not clamp the stranded wire without first soldering or crimping it with a tubular tip into a screw clamp.
The indisputable advantages of screw terminals include the ability to connect aluminum wires with copper, as well as the lack of need for subsequent insulation of the contacts.
However, this type of connection is not without drawbacks. He needs periodic maintenance, which consists in tightening the clamping elements. Copper is a very soft material, prone to "leakage" from under load. Even if the connections are made by means of rigidly spring-loaded self - clamping terminal blocks, due to the too small area of the contacting surfaces, the spring elements are heated and released under heavy load, as a result of which their elasticity decreases with the quality of the connection.
To ensure good contact, soldering or welding of copper wires is most often used. Which is the best of these methods? Definitely welding. The fact is that soldering is a rather laborious and lengthy process, especially if it is required to connect a multi-core copper cable. Plus, adhesive compounds break down over time due to the presence of a third, more loose and fusible metal - solder. The presence of transition resistance at the joints of different alloys contributes to the appearance of destructive chemical reactions and other negative processes.
When welding the copper wire, the concept of “contact” disappears altogether, since the connection is monolithic from the same metal. Naturally, such compounds are characterized by record low resistance, due to which heat is practically not released.
It should be noted immediately that this operation requires certain knowledge and experience. Paradoxical as it sounds, but high-quality twisting is better than bad soldering, remember this.
The soldering process begins with a preliminary cleaning of the ends of the wires from insulation and oxides. Then they are twisted, coated with a special substance - flux, and then soldered. You can solder not only copper wires, but also aluminum, the main thing is to choose the right flux and solder. The use of active acid flux is not recommended, since it will necessarily remain on the wires, as a result of which the connection will quickly break down.
One soldering takes a lot of time, however, if everything is done correctly, such a connection will be reliable and durable. After the wires have cooled, they must be carefully insulated.
The most high-quality and safe connection is made by welding copper wire. The resistance at the point of contact of the wires does not exceed the index of their standard resistance. This method does not require much time and is considered relatively simple. With minimal skills and knowledge, welding copper wires at home is quite feasible.
When carrying out welding work, it is necessary to strictly observe all fire and electrical safety rules. In order to avoid burns and eye injuries, personal protective equipment should be used - special protective clothing and mittens, a welding mask or goggles.
The connection of wires by welding is performed by devices of various types. It is most convenient to use an inverter apparatus for welding copper wires, since devices of this type are characterized by small dimensions and weight, economical energy consumption and a wide range of welding current adjustments. Their advantages include the ability to provide stable burning of an electric arc.
If a significant amount of electrical work is planned, then the purchase of an inverter-type welding machine will be quite appropriate and justified. Moreover, this equipment will certainly not be a “dead weight” in the future.
Features of the process of welding wires from copper
Welding a copper wire can be carried out either by alternating or direct current at voltage indices of 15-30 V. It is very good if the device provides for the possibility of adjusting the current.
For example, to weld two copper wires with a cross section of 1.5 square meters. mm, enough 70 A. For welding three wires with the same cross section, the current must be increased to 90 A. The connection of three wires with a cross section of 2.5 square meters. mm will require from 80 to 100 A, and for welding of five similar wires - 120 A. If the optimal welding current is selected, the electrode does not “stick” and the arc burns steadily enough.
For welding wires from copper, coal-copper “pencils” (electrodes) are used. If there are none, then it is possible to use carbon rods from finger-type batteries.
The ends of the wires 5-6 cm long are cleaned of the insulating coating and twisted, starting from the sections of insulation, leaving 5-6 mm at the end of the twist in an untwisted state. These tips must be straightened, folded in parallel and pressed against each other. When twisting three or more wires, at the end you still need to leave only two free ends, and cut off the rest in the place of the last turn of the twist. If the welding machine is not powerful enough, such twisting will make it easier to form a melt ball. If there is sufficient welding current in the machine, a simple twist can be performed.
Next, the twist is clamped using a welding clamp. If this device is not available, you can use the usual old pliers.
The prepared compound is welded with a carbon electrode. In the process of welding copper wires, the ends left untwisted are melted until a melt ball is formed. To ensure reliable mechanical and electrical contact of the wires, the melting zone must necessarily reach the twist.
The duration of welding should not exceed 2-3 seconds, otherwise the insulation of the wires will melt. After the compound is completely cooled, it is insulated using several layers of electrical tape or special caps, PVC or heat-shrink tubing.