Abstract:Causes of excessive contact resistance of cable jo...
Causes of excessive contact resistance of cable joints
1. Poor installation quality
(1) If the connecting wires are not twisted according to the regulations, or even connected by hooking, the connection of the joint will not be firm, and it is easy to loosen.
(2) The wires, switches, and electrical appliances are connected through wire posts. Due to sloppy construction, no washers are added to the posts, and the gong caps are not tightened, which will also increase the contact resistance. For example, in a restaurant, for this reason, the conductor melts in the distribution box, and the molten beads fall on the cardboard box below, causing a fire.
(3) The copper wire and the aluminum wire are not connected according to the prescribed method, which is often incompatible with each other, and the contact resistance is relatively large, causing hidden dangers.
(4) The cores of the multi-strand wires are not twisted well, and some of the hairs (cores) are warped outwards, forming a short circuit after touching each other. For example, a department store did not twist the multi-strand copper core wires well when installing the electrical socket. As a result, some copper wires were exposed and touched another phase line. After the power was turned on, a short circuit occurred, causing a fire.
(5) The joints of each phase line are not staggered during construction, and accidents will also occur on the same section. This kind of joint is direct, the disadvantage is that the insulation of the wrapping is not good, and it is easy to cause a short circuit, and the mechanical strength is not good. Chicken feet connection is recommended.
2. Loose joints in long-term operation. Some of them are of good quality during installation, but due to thermal expansion and contraction, or long-term vibration, the joints will become loose. For example, the electrical circuit in the bridgehead of a bridge, because of the strong vibration often generated when the vehicle crosses the bridge, gradually loosens the joint of the wire, the contact resistance gradually increases, and the heat becomes more and more serious, resulting in a fire.
3. Oxidation occurs at the conductor connection. In a humid and corrosive environment, an oxide layer is easily formed on the conductor (copper oxide will appear on copper wires, and aluminum oxide is more likely to be formed on aluminum wires). The conductivity of this oxide is poor. For example, in the electroplating workshop of a factory, the wires have been corroded by acid gases for a long time, and the conductors form an oxide layer on the surface, which increases the contact resistance, and generates high temperature after power-on. In severe cases, the wires even turn red. Fortunately, it was discovered in time, and there was no accident in the end.
4. Dust pollution On construction sites and other open air places, soil and dust often seep into the connection points of conductors, affecting the contact between conductors, overheating the connections, and causing nearby flammable objects to burn.
Measures to prevent accidents at joints
1. To minimize the wires that are often dragged by the cable joints of the wires, the whole wire should be used, and there should be no joints in the middle. In addition, in important places, such as the stuffy roof of the house, there should be no joints.
2. Pay attention to the quality of the connector
(1) The wire connection should conform to the specification. Try to increase the contact surface of the wire connection, and the hook connection method is prohibited. When connecting with a terminal, the multi-strand wires should be twisted tightly, and there should be no exposed filaments, and the wire needs to be bent into a ring, sleeved on the terminal, and gasketed. Screws, gong caps should be tightened.
(2) Pay attention to the connection method. The connection of large-section wires and aluminum core wires is easy to use welding method or crimping method (conductive paste can be applied when the crimping method is used). A layer of thin copper sheet coated with tin, or tinned on the copper wire nose, and then connected to the aluminum wire, this method can reduce the contact resistance.
(3) The position of the connector is staggered. The joints of the conductors of each phase should be staggered, and the joints should be covered with black tape. Wires with large cross-sectional area should be covered with yellow wax cloth or yellow wax silk to improve the insulation performance. As the saying goes, "fire before fire".
In electrical construction, attention must be paid to the above links to prevent fire accidents due to poor electrical connections.
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