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Various electrical connections and their requirements 1. Common forms and requirements of electrical connections: (1) Connection between lines 1. Basic requirements for connection: (1) The connection should be tight and stable, and the resistance of the joint should not be greater than 1.2 times the resistance of the wires of the same cross-section and length. (2) The joint must be strong, and its mechanical strength should not be less than 80% of the wire of the same cross-section. ； (3) The joints should be corrosion-resistant. When welding between wires, chemical corrosion of residual flux and slag should be prevented. ； (4) When copper and aluminum wires are connected, copper and aluminum transition connecting pipes should be used, and measures should be taken to prevent moisture, oxidation, and galvanic corrosion between aluminum and copper. ； (5) The restored insulation strength of the joint should be consistent with the original wire. 2. Connection of aluminum wires: (1) Mechanical cold crimping method This method is widely used for connecting single-strand aluminum (copper) wires. It can be used not only for single-core wires and multi-core wires, but also for wires and cables. Its principle is: Using cold-drawn seamless aluminum (copper) casing and special crimping pliers, the pressure of the crimping pliers is used to press the casing on the wire core, causing stress between the casing and the wire to achieve a tight combination and form a good conductive path. According to different crimping methods, mechanical cold pressing method is divided into full extrusion method (also known as ring pressing type) and partial cold pressing method. The former uses special crimping pliers to press the sleeve and the wire core inserted into the tube into a hexagonal shape. It is generally used for the connection of large-section wire cores (up to 50 square millimeters). ； The latter also uses special crimping pliers. After the wire core is inserted into the casing, some pits (grooves) are selectively pressed into the surface of the casing. It is more commonly used than the former. Generally used for connecting lines with smaller cross-sections (less than 10 square millimeters). The method and main requirements of mechanical cold crimping method are: A. Peel off the insulation layer at the connection end of the line. The length should be half the length of the casing plus 5 mm. ； B. Wash away the oil stains on the core conductor and the inner wall of the casing, then use emery cloth and a small wire brush to remove the oxide layer on the conductor and the inner wall of the tube, and then apply Vaseline zinc powder paste (or other anti-oxidation, cooling conductive paste) ； C. Insert the wire core into the casing. The end must hit the center of the casing. The outer diameter of the wire core and the inner diameter of the casing should match closely. The wire core must not be bent, cut off or filled with another wire core. ； D. When crimping, all extrusion methods must be pressed to the corresponding specified size according to the different cross-section sizes of the casing. ； For the local extrusion method, the corresponding number of pressure pits must be selected first according to the different lengths of the casing, and then the depth of the pressure pits must be selected according to the cross-section size of the casing. At the same time, both ends of the casing should be pressed first when crimping. Each pit must be pressed in one go and must not be withdrawn midway. There must be no cracks after pressing. (2) Tin soldering (brazing) connection method This method is mostly used for connecting larger cross-section aluminum (copper) cores. Its methods and requirements are: A. First prepare the welding solder, its composition is shown in Table 1: Table 1 Solder composition table (weight ratio) Metal name │ Purity │ Melting point │ Solder composition Tin 99 and above 232 60 Zinc 93 and above 420 40 B. Remove the conductor insulation at the line connection end, and remove the conductor oil and oxide layer to clean up the metallic luster ； C. Use an electric soldering iron to apply solder to the conductor, and rub it while applying so that the solder can stick tightly to the conductor. Solder paste should be used as flux, and acidic flux should not be used. ； D. Overlap the wire ends that have been coated with solder, then wrap the two wire ends three times on the other wire respectively, and cut off the remaining wires. ； E. After overlapping, use a soldering iron to fill the entire joint groove with solder. The solder should be even and dense. After cooling, immediately wipe the connector clean, then apply a layer of quick-drying bitumen paint, and then wrap it to restore the wire insulation. (3) Resistance welding connection method This method is often used to connect more than two single-core aluminum (copper) wires in parallel. The methods and requirements are: Remove 20 to 30 millimeters of insulation from the connection ends, then twist the ends together and cut them neatly with pliers, leaving a length of 20 to 25 millimeters. Apply a small amount of flux to the joints before welding. (4) Gas welding connection method This method is mostly used to connect large-section wires. The methods and requirements are: First remove a section of insulation from the connecting end, remove 60 mm from the 16 mm² wire, 80 mm from the 35 mm² wire, and 100 mm from the 70 mm² wire. Before welding, the two bare wire ends should be wrapped near the insulation layer with water-soaked asbestos rope, and the two wires should be tied together with iron wire. When heated to the melting point of the conductor (usually with a high-pressure blowtorch), apply flux, and with the help of the filling and stirring action of the flux, the metal wire cores at the end of the connection will fuse together. After the joint is welded, the residue and flux must be removed immediately (you can wipe the joint clean with cotton gauze dipped in water while it is hot). 3. Connection of copper wires. Copper wires have better physical, chemical and conductive properties than aluminum wires. In addition to the same method as the above-mentioned aluminum wire connection, the following methods can also be used to connect copper wires:: (1) Twisting method This method is mostly used for two "butt", three "T", and four "cross" connections of single core wires below 2.5 square millimeters. When "butting", it is required that the two wires are twisted in the middle for more than 3 turns, and the ends of the two wires are twisted on the other wire for more than 5 turns. At the same time, it is required to leave a gap of 10 mm between the ends and the insulation layer after twisting. ； When making a "T-shaped" connection, the connected wire ends are required to be twisted more than 5 times on the overlapping conductor, and there must be a 10 mm gap between the three ends and the insulation layer. ； When connecting in a "cross" type, the four connecting wires should be twisted for more than 5 turns on each of the wires to be connected, and a 10 mm gap should be left at the four ends after connection. (2) Winding method This method is usually used for butt jointing single core wires below 4 square millimeters. The form and requirements are:: Overlap the two wires to be connected and a bare conductor of the same quality and cross-section (the bare conductor is sandwiched in the middle of the two wires), and wrap it with a thin copper wire (generally 1.5 square millimeters) smaller than the cross-section of the wire to be connected. It is required to be wrapped The length should be more than 10 times greater than the diameter of the wire being connected. Then, the two ends of the bare conductor sandwiched in the middle are tilted up to form an elbow shape to strengthen the resistance to longitudinal stretching and prevent the joint from loosening. Wrap the thin copper wire around the outside of the two elbows for more than 5 turns each. After winding, a gap of 10 mm must be left between the two ends and the insulation layer of the two wire ends. The above method is also suitable for connecting small-section multi-core flexible wires, but the core wires must first be tightened into single-strand (core) wires and then connected. 4. Copper and aluminum wires are connected to copper and aluminum conductors. Due to their different physical, chemical and characteristics, in normal environments, the joints are prone to electrochemical reactions and corrosion, which significantly increases the contact resistance. Therefore, connections should be avoided as much as possible. When copper and aluminum connections must be made, the following methods are generally used: (1) Use copper or aluminum transition connecting tubes (connecting sleeves with one end made of copper and one end made of aluminum, and flash welding in the middle) for crimping or welding ； (2) Tin tin the contact surfaces of copper and aluminum conductors first, and then connect them ； (3) Tin the copper wire nose and connect it to the aluminum wire nose ； (4) Place tin foil (or tin-lined thin copper sheet) at the joints of copper and aluminum wires and then connect them. (2) Connection between lines and equipment This connection occurs between the wire heads and junction boxes, terminal blocks, (rows) and other power distribution and electrical equipment incoming and outgoing wire terminals or terminal bolts. In a sense, the connection between lines and equipment is more common than the connection between lines in actual electricity use. Although the connection processing is easier than the latter and the firmness is relatively strong, due to the large number of contacts, it is also one of the links most likely to cause poor electrical contact and cause safety accidents. Common connection forms and requirements mainly include: 1. Pressure connection is a connection method in which the wire head is inserted into the terminal hole and the screw is rotated along the threaded hole so that the rod head is directly pressed against the wire head. What is required and should be noted is that: (1) The size of the wire insertion hole must match the cross section of the wire. It is forbidden to reduce the cross-section of the conductor before inserting it into the hole. When the cross-section is too much smaller than the cross-section of the hole, the plug-in part of the conductor should be thickened and thickened. ； (2) Before the multi-core wire enters the jack, the outside should be wrapped with a thin metal skin with good conductivity, soft texture, strong anti-corrosion, to prevent the wire head from loosening and breaking when it is pressed by the screw head, which affects the electrical contact effect. Special attention should be paid to this point for commonly used aluminum conductors. 2. Side pressure connection is a connection method that uses wiring bolts to "hook" the wire around the screw and then turn the nut to tighten it. The requirements and things that should be paid attention to are:: (1) When conditions permit, formed wire head terminals should be used as much as possible, that is, the formed terminals should be connected to the wire heads first, and then the terminals should be crimped. ； (2) Small-section single-core copper wires (generally less than 10 square millimeters), multi-core copper wires (below 2.5 square millimeters), and single-core aluminum wires (below 2.5 square millimeters) can be directly connected to terminal blocks (including top-pressure type), but multi-core wires should be tightened and tinned before connection ； (3) When connecting multi-core and large-section single-core aluminum wires and large-section copper wires, the formed terminals should be welded or crimped first and then bolted to the equipment. ； (4) When the wiring nut is crimped to a single-core wire homemade terminal (i.e., bending the wire end into a semicircular hook-shaped terminal) or a formed terminal, a spring washer (generally made of high carbon steel and then blued) should be placed under the terminal (use an additional flat washer on the spring washer) so that the current flows directly to the flat washer → nut → screw without passing through the spring washer with high resistance to reduce contact resistance. ； (5) When two self-made terminal blocks are crimped with bolts, a metal flat washer should be added between the two terminal blocks to increase the wire contact area and reduce the contact resistance. ； (6) When current is transmitted from one conductor (A) to the other two conductors (B, C) through the connecting bolt, A should be sandwiched between B and C to prevent the heat generated by the electric energy transmission from being concentrated on one contact surface. ； (7) Sometimes for the purpose of measurement, a small cross-section wire is often clamped at the current incoming or outgoing busbar, switch blade, fuse and other connections. In order to reduce the contact resistance and temperature, it should be avoided to sandwich the small-section wire between two large-section wires so that the large-section wires are in direct contact. ； (8) For important wiring bolts such as electromagnetic switches, try to use "∧"-shaped wire crimping metal washers that are equivalent to the combination of spring washers and flat washers in wiring performance and have good anti-seismic and anti-loosening effects. However, an appropriate "∧"-shaped washer should be selected based on the cross-section size of the wire. That is, after the tightening nut is tightened, the lower edge of the "∧"-shaped washer should leave a gap of 0.5 to 1.5 mm from the plane of the bottom plate to prevent "reaction force" from hindering the increase in contact pressure. 2. Fire safety monitoring measures for electrical contact points: No matter how high the quality of the construction and installation of electrical contact points is, due to the influence of various factors during current-carrying operation, they will inevitably become loose and the contact resistance will increase over a period of time, resulting in increased contact heating, which is likely to cause a fire accident. In practice, the following measures are commonly used to monitor the operating status of important contacts for timely maintenance.: 1. Place the temperature test material, that is, stick a temperature-indicating wax sheet to the joint, apply temperature-indicating color-changing paint, and use the color change of the temperature test material as the joint temperature rises to determine whether the joint has a high temperature, thereby judging the joint contact condition. ； 2. Set point thermometer. For very important joints, thermometers are often installed to directly reflect the joint contact status by displaying the joint temperature. For example, using a semiconductor point thermometer ； 3. Infrared temperature measurement This is a non-contact temperature measurement and monitoring method for joints. It can detect joints for a long time or temporarily. ； 4. Observation method: First, you can observe the generation and rise of hot airflow near the joint; second, you can observe the melting of frost and snow at the joint. ； Third, you can observe the local drying of joints and steam rising in the rain, etc. There are many forms of electrical connections, and there are more and more new and advanced methods. The above are only some basic forms, requirements and safety measures for electrical connections. However, in practice, in order to effectively prevent fire accidents caused by poor contact, electrical connections should be avoided as much as possible. like: For mobile appliances, the entire conductor should be used ； When installing lines in flammable and explosive places, environments prone to corrosion, and environments with poor heat dissipation conditions (such as in the roof of a building), wires of appropriate length should be pre-fitted with a margin to avoid and reduce line joints. ； In line laying, the connections between wires and junction boxes, junction boxes, switch boards, control boards, terminal blocks, etc. can also be used to replace the joints of the line itself, etc. This post was last edited by yss5180 on 2008-1-27 14:12 ]