The metal casing of the electrical equipment must be grounded. Its main function is to determine the grounding voltage of the casing once the charged body is in contact with the device casing. In the event of a hazardous electrostatic voltage, static electricity can be quickly removed by grounding; when electrical equipment on the roof or outdoors is struck by lightning, the grounding of the electrical equipment casing can quickly spread the lightning current into the ground. Although the grounding of electrical equipment is important, it is not uncommon to have incorrect practices during construction. This article discusses the following aspects from the following aspects. 1 bolt and ground wire connection '. However, in actual operation, when the metal shell of the equipment is welded with the galvanized bolt, the galvanized layer is completely destroyed and the rust prevention effect is lost, especially in the open-air equipment, the bolt is rusted quickly, which affects the reliability of the grounding; Some construction units weld a piece of galvanized flat steel to the metal casing of the equipment and then connect it to the galvanized flat steel as a grounding wire with galvanized bolts. When this method is used to weld galvanized flat steel, since the galvanized flat steel is short, the galvanized layer of the galvanized flat steel is also damaged, which affects the reliability of the grounding. The correct way: on the metal casing of the electrical equipment, a copper grounding terminal is welded by chemical exothermic welding, and the terminal is connected with the grounding wire to achieve reliable grounding. The so-called chemical exothermic fusion welding is to use graphite casting mold to fix the copper terminal and the electrical equipment casing together, put the copper-aluminum alloy powder and the ignition powder in the welding mold, and ignite the ignition powder with the ignition gun to make the copper-aluminum alloy powder. A chemical reaction takes place to form a high-temperature copper melt that melts the shallow surface of the metal casing of the electrical equipment and fuses it with the copper ground terminal. In the project, the welding problem is often encountered between flat steel and flat copper. At this time, brazing can meet the requirements of electrical connection, but the flux of brazing is corrosive, and it is not easy to remove after welding, so it is easy to produce chemical corrosion. And chemical exothermic fusion welding does not have corrosive flux, called fluxless soldering, so there is no chemical corrosion. There is a potential difference between copper and iron, which will cause electrical corrosion. When the chemical fusion welding method is used, an alloy layer is formed between the copper and iron, thereby avoiding electrical corrosion due to the potential difference. Chemical exothermic welding has been widely used in power plant and other important engineering projects. With the gradual emphasis on grounding reliability, the application of chemical fusion welding is bound to become wider and wider. 2 There are three ways to ground the roof of the roofing equipment: 1) connect the metal casing of the electrical equipment above the lightning protection belt of the daughter to the lightning protection belt, and connect the electrical equipment shell of the lightning protection belt to the ground of the power supply; After the electrical equipment metal casing of the parapet wall is connected with the lightning protection belt, it is connected to the PE wire of the power supply; 3) The metal casing of the electrical equipment of the roof is connected only to the lightning protection belt, and is no longer connected to the PE wire of the power supply. According to the regulations: the lightning rod or lightning protection metal mesh on the building should be connected with other metal objects at the top of the building as a whole. In the above practice, it is wrong to connect the metal casing of the electrical equipment below the lightning protection band to the lightning protection belt. Because electrical equipment below the lightning rod and lightning protection belt is still subject to lightning strikes, the possibility of lightning strikes is greatly reduced due to the presence of lightning protection devices. Is it possible to connect the electrical equipment on the roof to the lightning protection belt? Connected to the PE line of the power supply, the relevant national regulations clearly state this end, but the lighting power line on the frame equipped with the lightning rod and the lightning protection line must use the cable with metal sheath buried directly in the soil or wear Wire into the metal tube. The metal sheath or metal pipe of the cable must be grounded, and the length buried in the soil should be more than 10m before it can be connected to the grounding grid of the power distribution device or to the power line and low-voltage power distribution device. Therefore, from the perspective of safety, the metal casing of the roof electrical equipment cannot be connected to the PE wire. If it is connected to the PE wire, once the electrical equipment is struck by lightning, part of the lightning current will enter the ground along the lightning protection line, and the other part will enter the room along the wire. When people touch the PE line at this time, they will be hurt by lightning current. The last of the above practices is correct, that is, the metal casing of the electrical equipment on the roof is only connected to the lightning protection belt. For the TT system, the metal casing of the electrical equipment located on the roof is connected to the grounding device through the lightning protection belt and the lightning protection down conductor. At this time, the lightning protection grounding also serves as the protective grounding, and the grounding resistance is not greater than 4. The lightning protection grounding device and the working ground of the power supply The distance between the device and the ground shall not be less than 3m. The TN system of the joint grounding body shall be adopted. Although the outer casing of the electrical equipment of the roof is only connected to the lightning protection belt, it is connected to the PE line, but the lightning protection down conductor leads to the underground and the grounding grid. After being integrated, the lightning protection down conductor is equivalent to the PE line and meets the grounding requirements. The specification has a distance requirement for the connection point between the lightning protection down conductor and the grounding grid, that is, the underground connection point between the lightning rod and the main grounding grid to the underground connection point of the equipment and the main grounding grid of 35KV and below, and the length along the grounding body shall not be less than 15m. 3 The distribution of PE wires in the busway is very common for the distribution of high-rise buildings. The busbars are divided into three, four and five wires. For three-phase power distribution, some designs use three-wire busway, and some use four-wire busway; for three-phase power supply distribution, some designs use four-wire busway, and some use five-wire busway; Three-wire power distribution or four-wire lighting distribution system, the PE line is laid separately outside the busway, for the four-wire power distribution or five-line lighting distribution system, the PE line and the phase line (neutral line) are on the same bus. Inside the slot. For busbar slots with PE wires, if the pins are pulled out from the PE wires in the busbar slots, the pins are not properly secured when the pins are inserted or the elastic pieces of the pins are insufficiently elastic. Using the pin to lead out the phase line, a phase loss occurs soon, but it is not easy to find out. If it is found, it is often too late to have an electrical accident. Therefore, it is not advisable to use the PE wire to lead out. At present, some manufacturers do not use pin-outs for the busbars of 400A and above, including the phase line, and instead use argon-arc welding to weld the joints and bolt them. Obviously, the grounding reliability is better than that of the pins. If the PE wire is laid separately outside the busway, bolting can be used, which can reduce the construction cost and facilitate inspection. 4 Conclusion Grounding protection Although it is affirmed by various electrical codes in China, serious defects in the construction of the site can not be ignored. Practice has proved that only the construction according to the requirements of the electrical code, using scientific welding technology, can ensure the reliability of grounding safety. Sex. Han Feng. Building Electrical Design Handbook 丨M. Beijing: China Building Industry Press, 1991. Beijing: China plans to publish, 1999. (Editor: Liu Cunying) Stripe Fabric ,Striped Upholstery Fabric,Black And White Striped Fabric,Striped Linen Fabric JIANGYIN JINPENG YANR-DYED FABRIC CO LTD , https://www.jinpengfabric.com