A ground wire, also known as a lightning cable, is a wire used to introduce an electric current to the earth. When electrical equipment leaks, an electric current enters the ground through the ground wire. The symbol of the ground wire is E (Earth), which can be divided into two types: power supply ground wire and circuit ground wire. According to the current standard of the mainland, the third article in GB/T6995.4-2008 marks the circuit according to the color of the wire:
Generally, it should be a phase line - A phase yellow, B phase green, C phase red. Neutral wire - light blue, the ground wire is a combination of green and yellow, if it is a three-phase socket, the left is the neutral wire, the middle (top) is the ground wire, and the right is the live wire.
Ground Classification:
(1) Power supply ground: from the transformer neutral point grounding after the main line, according to the standard, every 20-30 meters interval repeated grounding, in the circuit to play a role in safety protection. In the case of leakage, the consumer and the ground wire form a parallel circuit. With the ground wire, because the resistance of the ground wire is relatively small, the current will flow quickly into the ground, and the user will avoid electric shock. Causing disability. In practice, it is usually a yellow and green wire.
Ground wires are very important in household electricity, but there are no ground wires in the power supply network in some areas, which can be remedied by the following methods. Find a place outside the house, take a 50-70mm wide, 1-2 meters long angle iron into the ground, and then connect the ground wire to the angle iron, it is best to fix it with bolts when connecting, the connecting wire is as thick as possible, 6-10 square millimeters, and then reduce the grounding resistance can be poured a little salt water around the angle iron.
(2) Circuit ground: In the circuit design, the main thing is to prevent interference and improve the radiation efficiency of radio waves. The ground wire is widely used as a reference point for the potential, providing a reference potential for the entire circuit.
In this case, the ground wire is not necessarily connected to the true earth, but is often connected to one of the input power lines (usually the neutral wire), and its potential is not related to the earth potential. When the whole circuit is designed, the voltage on the ground wire is 0V to unify the potential of the whole circuit.
In recent years, home improvement has used leakage circuit breakers, and the correct configuration is to install a two-pole total circuit breaker into the home line, and the total circuit breaker is two branches, one way for lighting.
The other way is for the socket, lighting does not need to install a leakage circuit breaker, the socket should be reasonably configured with a leakage circuit breaker, (home improvement action current 30mA), if the leakage circuit breaker is installed, and the ground wire is connected, it is good from the perspective of personal safety, but it may increase the probability of the circuit breaker action, that is, the leakage current is not because of the human body flow through and the protective action.
If the leakage circuit breaker is sensitive, but there is no ground wire, when there is leakage current flowing through the human body, the leakage circuit breaker will act and there will be no personal injury.
As long as the leakage circuit breaker is fine, it is safe to have no ground wire, and it is not necessary to consider the ground wire.
The ground wire plays a protective role, and the shell of the electrical equipment is connected to the ground wire through a plug. Once the socket grounding wire leaks, the shell of the electrical equipment will be electrified, but due to the role of the ground wire, ensure that the electrical shell and the ground wire are equal to the potential, that is, the voltage to the ground is equal to 0, so as to ensure the personal safety of the electrical user.
How to judge the home socket grounding wire first cut off the total power supply in the house, find a long wire, a flashlight bulb and a large battery, plug one end of the long wire into other sockets (can be the socket of this house or other houses) in the ground wire, one end is connected to the battery and then the bulb, the other end of the bulb is thrown out and plugged into the socket ground wire to be measured, use the ground wire in the house to make a circuit, the bulb is no problem, try all the socket ground wires, prove that all the ground wires in the house are fine!
Phase wire, neutral wire, grounding wire knowledge household electricity, standard single-phase users have three wires, phase line L, neutral line N and grounding wire PE, neutral line N and phase wire with the same cross-section, grounding wire PE is 2.5 square millimeters, double color.
The protection of household electricity is completed by the wiring of the socket plug, and the wiring principle of the plug and socket is: the left zero and the right phase are grounded. It is the plug-in connection between the shell and the plug of the household appliance, the plug-in connection between the grounding wire and the socket from the outside, and the reliable connection between the shell of the household appliance and the earth to realize the safety protection of electricity.
Ground and neutral wires cannot be mixed:
1. The neutral wire of the neutral line and the transformer is directly connected, and the live wire directly forms a loop, without voltage drop loss;
2. The grounding resistance of the neutral line and the neutral wire is very high, the grounding resistance of the transformer below 100KVA cannot be higher than 10 ohms, and the grounding resistance of the transformer above 100KVA cannot be higher than 4 ohms;
3. The grounding wire is connected with the neutral line and the neutral wire at the transformer, and it will be independent in the future, and the grounding will be repeated to the distribution box, but the grounding resistance is only 30 ohms or less.
4. The cross-sectional area of the neutral wire and the live wire is the same, and the ground wire is generally 2.5 square millimeters, and the larger current cannot be passed, so the grounding wire cannot be used as the neutral line;
5. There is no grounding wire for users, household appliances are not grounded, and they can't get the grounding wire by themselves (if they are unqualified, the harm is greater), and they can't use the zero wire as the grounding wire, (when the three-phase current is unbalanced, the zero line is live, and the shell of the household appliance is also pointed, and the shell of the household appliance is directly connected to the thermal power when the zero wire is broken, which is more dangerous.) ) will affect the normal operation of the power system.