I. Introduction.

The AC power cord is divided into a neutral wire, the symbol letter is'N' and the fire wire, and the symbol letter is'L'. Also connected to electrical appliances is the ground wire-the wire connected to the earth;

The live wire, neutral wire, and ground wire are all wires connected to the three-hole socket, and a sinusoidal oscillation pressure difference is maintained between the live wire and the neutral wire. Since the earth and the neutral wire have the same potential, the live wire and the ground wire also maintain a sinusoidal oscillation pressure difference.

When the human body touches the live line, the person is standing on the ground. The current of the live line flows into the ground or the neutral line through the human body, and an electric shock will occur, while the neutral line will not be shocked. Connect the shell of the electrical appliance whose shell can conduct electricity to the ground wire. In the case of electric leakage, the current will directly flow into the earth through the ground wire without passing through the body, thereby avoiding electric shock accidents.

In fact, it’s hard to say the specific situation of the zero line and the live line is charged, but from experience, one is that the neutral line is charged due to the bias. This situation is inevitable in the power grid, and the voltage of the neutral line will not be too high, as long as it is not biased. Too outrageous does not affect normal use.

There is also a problem that the neutral wire is broken. Take our ordinary building example, one is that the neutral wire of the home is broken. In this case, the electrical appliances will not work but will not cause damage to the electrical appliances, as long as the user does not privately Disassembly and investigation will generally not cause electric shock injury.

The other is that the neutral wire in the unit circuit is broken, which is rare, but it is very harmful.

Second, the cause of the three-phase neutral line being charged

(1). The neutral line is charged with a lack of good grounding. If it is well grounded, the current will flow into the ground and the meter will not be able to detect it. In short, as the two upstairs said, either the zero line is broken or the contact is not good. However, this is actually the result; not the cause of the neutral line being charged.

 (2) Under normal circumstances, there should be no electricity on the zero line. Therefore, once there is electricity, it must be a fault; the simplest is electromagnetic induction, and the neutral line is not well grounded at this time, and no loop is formed; secondly, the electrical equipment leaks or the phase line touches the shell, but the current is not too large. , So there is no trip.

 (3) The electrical equipment is leaking or the phase line is touching the shell, but the current is not large, so there is no tripping. In a three-phase four-wire power supply system, if the neutral wire is not well grounded or the ground terminal is broken, the consequence is that the potential of the neutral wire is not equal to 0 when the three-phase load is unbalanced, that is to say, the neutral point is biased. shift.

The specific zero line potential is related to the degree of unbalance of the three-phase load. The more unbalanced, the greater the offset of the neutral point and the higher the potential of the zero line. After the zero line potential shifts, the phase voltage of the three phases is generally not 220V. Some phases may exceed 220V, and some phases may be lower than 220V.

If the offset of the neutral point is too large, the phase with the increased phase voltage of the three-phase may cause the electrical appliances to burn out, and the phase with the reduced phase voltage of the three-phase may cause the electrical appliances to fail to work. After the potential of the neutral line rises, when it reaches a certain value, it will cause an electric shock accident if it touches the ground line.

(4) The neutral wire is broken, making the neutral wire live

(5) In the connection to the power grid, some individuals use grounding for the protection of electrical appliances, so that the neutral line is charged.

(6) When a long cable is used for power supply, the induction charging when the electric equipment is not in use, when the equipment is used, this phenomenon will automatically disappear

(7) The neutral line is directly grounded, and the system neutral line is not connected

(8) The zero wire and the live wire overlap

(9) When the three-phase power load is unbalanced, zero potential drift will occur and voltage will be generated.

2. General measures for neutral line electrification

(1) Focus on checking the connection mode and connection effect of each connection of the neutral line.

(2) The neutral line must pass all phase currents. Generally, the area of the neutral line must be large enough, or multiple neutral lines need to be arranged from the main switch box.

(3) Investigate wire breakage caused by various reasons, such as accidental injury caused by external forces such as wall drilling.

(4) If the zero line flickers caused by turning on the light, please check whether the lamp cap has a short circuit and the quality of the light switch. If the zero line of all parts is dotted, please check the zero row of the main switch box; If the zero row is charged, the problem lies in the zero line before the zero row.

3. Specific analysis of specific issues

(1) There is electrical equipment leakage on the line, but the protection device does not operate, making the neutral line live.

Solution: Perform maintenance after power failure, find out the leaking equipment for repair, and find out the cause of the failure of the protection device.

(2) There is a phase grounding on the line, and the main protection device in the power grid is not protected to make the neutral line live.

Solution: After a power failure, first use a shaker to measure the line to see if the line has poor insulation. When measuring, pay attention to disconnect the meter in the line.

(3) The neutral line is broken, and there is electric leakage in the electrical equipment behind the break or there is a large single-phase load operation, which makes the neutral line live.

Solution: After power failure, test whether the zero line is broken, find and repair the broken.

(4) In the zero-connected power grid, some electrical equipment adopts protective grounding and leakage, which makes the neutral line live.

Solution: Distinguish whether the system is connected to the zero system or the grounding system, or repeated grounding in the zero connection system. Then install the ground wire correctly.

(5) In the zero-connected power grid, there are single-phase electrical equipment using "one fire, one ground", that is, no working zero line, so that the zero line is charged.

Solution: Install the N wire, and the PE wire cannot be used as the N wire.

(6) The insulation resistance of some electrical equipment in the power grid has been damaged and leaked, making the neutral line live.

Solution: Check the equipment whose insulation resistance does not meet the specified requirements and repair it.

(7) The working ground connection at the low-voltage side of the transformer has poor contact and large resistance. When the unbalanced current of the three-phase load exceeds the allowable range, the neutral line is charged.

Solution: poor contact is difficult to find, and maintenance should be carried out every year or according to the specified time. Don't be lazy, and carry out maintenance according to the regulations.

(8) High voltage flees into low voltage to make the neutral line live.

Solution: It is difficult to find, and sometimes there will be big problems. The most difficult one to deal with is dangerous to people. Be sure to follow the operating procedures.

(9) The high voltage adopts two-wire one-ground operation mode. When the grounding body is too close to the low-voltage working ground or repeated grounding body, the voltage drop on the high-voltage working ground will affect the low-voltage side working ground and make the neutral line live.

Solution: Find out the reason and lay it according to the corresponding regulations.

(10) The magnetic field induces the neutral line to be charged.

 Solution: Prevent magnetic field induction.