In actual work, some beginners will simply think that the zero line is the ground line, and the difference between the PE line and the PEN line often used in the power system is not well understood. In the low-voltage installation maintenance and overhaul, the various protection wirings of the household appliances are often confused, resulting in confusion and error in the protection wiring of the electrical appliances, causing unnecessary troubles, and even causing electric shock accidents. Therefore, Xiaobian will give a brief introduction to the meaning of various "lines" in the 380V/220V power system for reference. The phase line, commonly known as the hot line, is relative to the neutral line (neutral line) and refers to any of the three phase lines L1, L2, and L3 in the three-phase AC circuit. Usually, household electricity uses only one of the three-phase power. The phase-to-ground (neutral) voltage is 220V, called the phase voltage. It forms a loop with the neutral line to make the current work through the household appliance. The voltage between the phase lines of different phases is 380V, called the line voltage. Normally, the three phase lines L1, L2, and L3 in the three-phase circuit are marked with three colors of yellow, green, and red, respectively. In the three-phase four-wire or three-phase five-wire low-voltage power supply system, the neutral line is also called the neutral line, the neutral line, the working zero line, and the N line, and the line is marked with black. Usually the neutral line is a line drawn from the neutral point of the transformer. For the grounded grid, the neutral point of the transformer must be grounded, and the grounding resistance is generally not allowed to be greater than 4 Ω. The role of the neutral line is to keep the phase voltages of the star-connected three-phase asymmetric load symmetrical. For a three-phase symmetrical load, since the neutral current is zero, the neutral line can be omitted. For a three-phase asymmetric load, due to the neutral current, there must be a neutral line balancing the voltage of the three-phase load. Otherwise, the phase voltages of the three-phase asymmetric load are no longer equal (balanced), and the impedance is small. Phase load voltage is low, and the phase with high impedance has a high load voltage, which may cause damage to household appliances. Therefore, in a low-voltage power supply system with asymmetric three-phase load, it is not allowed to install a fuse and a separately controlled switch device on the neutral line, and the neutral wire is usually made of steel-cored aluminum stranded wire to avoid neutral disconnection. have an accident. The difference between the phase line and the neutral line is that they have different voltages to ground, and the phase-to-ground voltage is 220V. Under normal conditions, the neutral-to-ground voltage is zero. The protection wire (also called PE wire, the English name is protecting earthing), is a wire that is connected to the earth through a deep buried electrode, which is what we usually call the ground wire, which is specially used to ground the exposed conductive part of the electrical device. conductor. The protection line can be divided into a working ground line and a protective ground line. In the low-voltage power system, the connection line between the neutral point of the transformer and the working grounding body is called the working grounding wire; the connecting line between the metal casing of the household appliance and the protective grounding body is called the protective grounding wire, and is represented by two colors of yellow and green. In the TT system, the PE line is directly connected to the grounding pole independent of the working ground of the power supply point, also known as the PEE line; in the TN-C system, the PE line and the neutral line of the whole system are unified; In the S system, the PE line of each electrical appliance is directly connected to a dedicated public PE line in the low-voltage power supply system, and the public PE line is to be reliably connected to the working ground of the transformer; in the TN-C-S system, the low-voltage side of the transformer is supplied to the user. A section of the line between the incoming points, the PE line is connected to the common neutral line, the user power inlet point to each appliance has a common PE line, and the PE line of each electrical appliance is connected to the common PE line. Protecting the neutral line (also called PEN line, protecting the neutral conductor), the color of the mark is the light blue of the vertical strip, which is the conductor that combines the PE line and the N line into one, and has the functions of the protection line and the neutral line. In the TN-C system of the low-voltage power system, the PE line and the N line are combined into one in the whole line; the TN-C-S system, a line between the low-voltage side of the transformer and the incoming point of the user power, and the PE line and the N line are combined. The second is one; the TN-S system separates the PE line from the N line. The power supply system uses PEN lines, usually to save material, but reduces the reliability and safety of the power supply. Wherever possible, low-voltage power supplies should use the TN-S system to the greatest extent possible, that is, deploy a completely separate PE protection line instead of the TN-C system that bundles the N-wire and PE lines together. Special reminder: The power supply safety requirements are relatively high, especially in places where there is a risk of explosion, the TN-S system must be used for power supply. The neutral line (N line) is connected to the neutral point of the transformer and can maintain the symmetry of the three-phase asymmetric load voltage and transmit electrical energy. In a single-phase system, without it, various electrical appliances cannot work normally. From this perspective, the N line is a work line and is indispensable. The protection line (PE line) is the ground wire connected to the outer casing of the electrical equipment. Without it, the electrical equipment can work normally, and it is not indispensable. However, if the electrical enclosure is charged due to a fault, there is no possibility that an electric shock may occur to a person who is in contact with the metal casing of the electrical appliance. It can be said that the role of the protection line is to prevent the occurrence of electric shock accidents, and therefore to protect the wires. Because of the presence or absence of the protection line, it does not affect the normal operation of the electrical appliance, and therefore, it is not taken seriously in the low-voltage users. At present, some urban households in China and a large number of rural households use electricity. There are many electrical appliances (Class I appliances, that is, electrical appliances with three-pin plugs) that are connected to the protection line. There is no connection protection line, which leads to safety hazards when using these appliances. Should be given enough attention. 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