A very complete summary of the basic knowledge of ground wire
[Copy link]
The main function of the ground wire is that when an electrical appliance fails, the power supply may break down (or: destroy) certain components, making the outer shell of the appliance charged. Grounding the outer shell of the appliance can enable leakage protection devices.
1. Signal "ground";
signal "ground" is also called reference "ground", which is the reference point of zero potential and the common section of the circuit signal loop, with the graphic symbol "⊥".
1) DC ground: DC circuit "ground", zero potential reference point.
2) AC ground: the zero line of AC power. It should be distinguished from the ground line.
3) Power ground: the zero potential reference point of large current network devices and power amplifier devices.
4) Analog ground: the zero potential reference point of amplifiers, sample-and-hold devices, A/D converters and comparators.
5) Digital ground: also called logic ground, which is the zero potential reference point of digital circuits.
6) "Hot ground": The switching power supply does not need to use a transformer. The "ground" of its switching circuit is related to the mains power grid, the so-called "hot ground", which is charged, with the graphic symbol: "".
7) "Cold ground": Since the high-frequency transformer of the switching power supply isolates the input and output ends; and since its feedback circuit often uses optocouplers, which can transmit feedback signals and isolate the "grounds" of both sides; the ground at the output end is called "cold ground", which is not charged. The graphic symbol is "⊥".
2. Protective "ground":
Protective "ground" is a wiring method set up to protect personnel safety. One end of the protective "ground" wire is connected to the electrical appliance, and the other end is reliably connected to the earth.
3. "Ground" in audio.
1) Shielded wire grounding: In order to prevent interference, the metal casing of the audio system is connected to the signal "ground" with a wire, which is called shielded grounding.
2) Audio-specific "ground": In order to prevent interference, professional audio, in addition to the shielded "ground", must also be connected to the audio-specific "ground". This grounding device should be specially buried, and should be connected to the corresponding grounding terminals of the isolation transformer and shielded voltage-stabilized power supply as a dedicated audio grounding point in the sound control room.
Different ground wire processing methods
1. Digital ground and analog ground should be separated;
in high-demand circuits, digital ground and analog ground should be separated. Even for A/D and D/A converters, it is best to separate the two "grounds" on the same chip, and only connect the two "grounds" at one point in the system.
2. Floating ground and grounding;
System floating ground means floating the ground wires of each part of the system circuit and not connecting them to the earth. This connection method has a certain anti-interference ability. However, the insulation resistance between the system and the ground cannot be less than 50MΩ. Once the insulation performance decreases, it will cause interference. Usually, the system floating ground and the chassis grounding are used to enhance the anti-interference ability and make it safe and reliable.
3. One-point grounding;
in low-frequency circuits, there will not be much impact between wiring and components. Usually, circuits with frequencies less than 1MHz use one-point grounding.
4. Multi-point grounding.
In high-frequency circuits, parasitic capacitance and inductance have a greater impact. Usually, circuits with frequencies greater than 10MHz use multi-point grounding. In addition to correct grounding design and installation, the grounding of various different signals must also be correctly processed. In the control system, there are roughly the following types of ground wires:
(1) Digital ground: also called logic ground, which is the zero potential of various switch quantity (digital quantity) signals.
(2) Analog ground: It is the zero potential of various analog quantity signals.
(3) Signal ground: Usually the ground of the sensor.
(4) AC ground: The ground wire of the AC power supply, this ground is usually the ground that generates noise.
(5) DC ground: The ground of the DC power supply.
(6) Shielded ground: Also called chassis ground, it is set to prevent electrostatic induction and magnetic field induction.
The above ground wire processing is an important issue in system design, installation, and debugging. Here are some opinions on the grounding issue:
(1) The control system should adopt single-point grounding. Generally speaking, high-frequency circuits should be grounded at multiple points nearby, and low-frequency circuits should be grounded at one point. In low-frequency circuits, the inductance between wiring and components is not a big problem, but the interference of the loop formed by grounding is very large. Therefore, one point is often used as the grounding point; but single-point grounding is not suitable for high frequencies, because at high frequencies, the ground wire has inductance, which increases the ground wire impedance, and at the same time, inductive coupling is generated between the ground wires. Generally speaking, when the frequency is below 1MHz, a single point grounding can be used; when it is higher than 10MHz, multiple points grounding can be used; between 1 and 10MHz, a single point grounding or multiple points grounding can be used.
(2) The AC ground and the signal ground cannot be shared. Since there will be a voltage of several mV or even several V between two points of a power ground line, this is a very important interference for low-level signal circuits, so it must be isolated and prevented.
(3) Comparison between floating ground and grounding. The whole machine is floating, that is, each part of the system is floating on the ground. This method is simple, but the insulation resistance between the whole system and the ground cannot be less than 50MΩ. This method has a certain anti-interference ability, but once the insulation decreases, it will cause interference. Another method is to ground the casing and float the rest of the parts. This method has strong anti-interference ability, is safe and reliable, but is more complicated to implement.
(4) Analog ground. The connection method of the analog ground is very important. In order to improve the ability to resist common-mode interference, shielded floating technology can be used for analog signals. The grounding treatment of specific analog signals must be designed strictly in accordance with the requirements in the operation manual.
(5) Shielded ground. In order to reduce the capacitive coupling noise in the signal, accurately detect and control it in the control system, it is very necessary to adopt shielding measures for the signal. Depending on the purpose of shielding, the connection method of the shielding ground is also different. Electric field shielding solves the problem of distributed capacitance and is generally connected to the ground; electromagnetic field shielding mainly avoids interference from high-frequency electromagnetic field radiation such as radar and radio stations. It is made of low-resistance metal materials with high conductivity and can be connected to the ground. Magnetic field shielding is used to prevent magnetic induction of magnets, motors, transformers, coils, etc. Its shielding method is to close the magnetic circuit with high magnetic permeability materials, and it is generally better to connect to the ground. When the signal circuit is grounded at one point, the shielding layer of the low-frequency cable should also be grounded at one point. If the shielding layer of the cable has more than one location, noise current will be generated, forming a noise interference source. When a circuit has an ungrounded signal source connected to a grounded amplifier in the system, the shield at the input end should be connected to the common end of the amplifier; conversely, when a grounded signal source is connected to an ungrounded amplifier in the system, the input end of the amplifier should also be connected to the common end of the signal source.
The grounding of electrical systems must be classified according to the requirements and purposes of grounding. Different types of grounding cannot be simply and arbitrarily connected together. Instead, they must be divided into several independent grounding subsystems. Each subsystem has its own common grounding point or grounding trunk line. Finally, they are connected together to implement total grounding.
The difference between ground wire and neutral wire
We know that when installing electrical appliances, we first use an electric pen to distinguish the live wire and the neutral wire. If there are only two incoming wires, one of which is the live wire and the other is the neutral wire, when distinguishing, the human body should not have any direct contact with the ground. Hold the electric pen with one hand, and do not touch the metal part of the pen tip, but the finger should touch the metal at the end of the pen. Touch the metal parts of the two wires with the pen tip. If only one of them can make the neon bulb of the electric pen light up, then this is the live wire. If neither of the two wires can make the neon bulb of the electric pen light up, it may be that the metal part is not touched or the power is not connected, or the electric pen is broken, or the finger does not touch the metal part of the end of the pen. If both wires can make the neon bulb light up, then the neutral wire is disconnected.
Detailed differences between the ground wire and the neutral wire
1. The neutral wire and the ground wire are different concepts, not the same thing, and must not be interchanged or mixed.
2. The ground wire has a zero potential to the ground, which is the nearest grounding.
3. The neutral wire’s potential to the ground is not necessarily zero. The neutral wire is grounded at the nearest substation, and there may be a certain potential difference with the local grounding.
4. The neutral wire sometimes shocks people. When the live wire has electricity but the device does not work, it may be that the neutral wire is broken. The neutral wire near the end of the device from the breakpoint is 220V, the same as the live wire.
How to distinguish the neutral wire from the ground wire
1. Wiring standard: The live wire (L) must be red, yellow, and green. The neutral wire (N) must be black and blue. The ground wire (PE) must be yellow and green. Facing the 3-hole socket, the left is the neutral wire, the right is the live wire, and the middle is the ground wire.
2. Install a residual current circuit breaker on the bus, and connect a light bulb to the live wire and the neutral wire or the live wire and the ground wire. If the residual current circuit breaker works, it means it is the ground wire, otherwise it is the neutral wire. Pay attention to safety when testing. There may be small sparks. Be prepared and don't be startled!
3. If you are at home: 1. Turn on the power and test with a test pen. All the wires that light up are live wires. 2. Disconnect the neutral wire at the main switch and only connect the live wire. Turn on the lights at home and test with a test pen. It was not bright just now, but now it is all the neutral wires that light up. 3. The remaining unlit ones are all ground wires.
The simplest way is to take a 220V light bulb, use an electric pen to determine the live wire, and connect two wires and the live wire to the lamp holder. You can distinguish between zero and ground from the brightness. The bright one is zero, and the slightly darker one is ground.
4. Use a multimeter to set the multimeter to the AC gear of 500V, hold one test pen in your hand, and touch the power line with the other test pen. The one with high voltage is the live wire, the one with low voltage is the neutral wire, and the one with 0 voltage is the ground wire. The neutral wire to ground resistance is less than 4 ohms for reliable grounding. Use a multimeter to set the AC gear of 250V to measure the voltage difference between the live wire and the neutral wire, and the live wire and the ground wire. The difference between the two values is less than 5V for reliable grounding.
The consequences of connecting the ground wire and the neutral wire incorrectly
1. Because it is AC power, the interchange of live and zero wire has no effect on electrical appliances. Facing a 3-hole socket, the left is zero and the right is live, which is mainly used for maintenance. It is better not to change it.
2. Zero and ground are connected reversely or mixed. This is usually fine, but it is more dangerous. The ground wire cannot be connected to the neutral wire. Otherwise, the device casing will be charged. (Generally, the casing is almost not charged when the device is normal)
3. The ground wire entering the house can be used as a neutral wire temporarily (the meter will not turn, which is considered stealing electricity), but if you want to use it for a long time, there are many unfavorable factors, such as: voltage instability due to changes in the grounding point environment (thunderstorms, humidity, etc.); substation factors make the live wire to ground voltage reach 380V, etc., which can easily affect and seriously damage electrical equipment.
In order to make AC power have a convenient power conversion function, power transmission is usually in the form of three-phase four-wire. The three ends of three-phase electricity are called phase wires. The
three tails of three-phase electricity are connected together and called neutral wire, also called "zero wire". The reason for calling it zero wire is that no current flows through the neutral wire when the three phases are balanced. In addition, it is directly or indirectly connected to the earth, and the voltage with the earth is close to zero.
The ground wire is a line that reliably connects the outer shell of the equipment or electrical appliances to the earth, and is a good solution to prevent electric shock accidents. Under normal circumstances, the live wires in the three-phase circuit are represented by red, yellow, and blue, and the neutral wire is black. In the single-phase lighting circuit, yellow is generally used to represent the live wire, blue is the neutral wire, and the yellow-green is the ground wire. In some places, red is used to represent the live wire, black is used to represent the neutral wire, and the yellow-green is used to represent the ground wire.
The colors and functions of the live wire, neutral wire and ground wire
From the national identification of the power cord, the phase wire is generally yellow for phase A, green for phase B, and red for phase C. The neutral wire is light blue. The ground wire is yellow and green. If it is a three-phase socket, the left side is the neutral wire, the middle (above) is the ground wire, and the right side is the live wire.
Generally speaking, the live wire is yellow, green, red, white, gray, and brown, the neutral wire is light blue and blue, and the ground wire is double yellow and black.
From the perspective of electricity consumption, it is divided into power electricity and household electricity. Power electricity is the commonly known 380-volt electricity, which is mostly used in factories and some large electrical equipment such as 5P air conditioners and restaurant smoke extractors. This kind of electricity is mostly three-phase four-wire. There are three live wires and one neutral wire in the four-wire. The live wire refers to any phase of the three-phase four-wire power grid ABC, and the neutral wire refers to the wire that has no voltage and current to the ground in the three-phase four-wire. The three live wires pass through the load such as electric motors and other electrical equipment and pass through the neutral wire to form a loop, so that the equipment can work normally. The neutral wire is grounded in the power plant. Under normal circumstances, the live wires in the three-phase circuit use red, yellow, and blue to represent the three live wires, and the neutral wire uses black or blue.
Household electricity refers to the 220-volt electricity we often call, also called single-phase electricity, which has two wires, one live wire and one neutral wire. The live wire passes through the load such as light bulbs and other electrical appliances and then forms a loop through the neutral wire, so that the electrical appliances can work normally. The neutral wire here is also grounded in the power plant. In the single-phase lighting circuit, yellow, green, red, white, gray, and brown generally represent the live wire, light blue and blue are the neutral wire, and yellow-green and black wires are the ground wire.
Although the neutral wires of power electricity and household electricity are grounded in the power plant, the ground wire and the neutral wire we usually talk about are not the same concept. Look at the three-hole power socket in our home. If it is a formal construction, one hole is the live wire, one hole is the neutral wire, and one hole is the ground wire. The ground wire here is grounded after the whole building is gathered, which is what is commonly called the ground wire. Most household appliances require a ground wire, that is, they must be connected to this ground wire. Generally, the neutral wire passes through the leakage switch, but the ground wire cannot. The ground wire has a zero potential to the ground, and the nearest point of the electrical appliance in use is grounded; the neutral wire's potential to the ground is not necessarily zero, and the nearest grounding point of the neutral wire is at the substation or the power transformer; the neutral wire can sometimes shock people, for example, if the electric stove does not heat up, don't think that there is no electricity and it will not shock people. There is such a possibility that the N line is disconnected far away from your electrical appliance. If you use a voltmeter to measure it, you will find that the LN line of the electrical appliance is the voltage of the mains; the ground wire will not shock people, unless it is very bad or the installer does not understand or messes up. In some circuits, there are neutral wires and ground wires, and you will find that there is a high-voltage capacitor between them.
The live wire is charged, and the ground wire and the neutral wire are not. There is a live wire and a neutral wire in a two-pin socket for household use. The live wire can be measured with a test pen, and the live wire is charged, and the neutral wire is not charged. There is a ground wire in a three-pin socket, and the ground wire should be connected to the outer shell of the electrical appliance to prevent the electrical appliance from leaking electricity and causing electric shock casualties. The point marked with L is for the live wire, the point marked with N is for the neutral wire, and the ground wire has a special grounding symbol.
At present, most of the power sockets we use are single-phase three-wire sockets or single-phase two-wire sockets. In a single-phase three-wire socket, the middle is the ground wire, which also serves as a positioning function; the wiring sequence is left zero and right live. All household appliances with metal shells use single-phase three-wire power plugs. The three plugs are arranged in an equilateral triangle, and the longest and thickest copper plug on the top is the ground wire. The two below the ground wire are the live wire (marked with the letter "L") and the neutral wire (marked with the letter "N"), and the sequence is left zero and right live (when the back of the plug is facing yourself).
Types and functions of grounding Different circuits have different grounding methods. The following are the common grounding methods in electronic power equipment:
1. Safety grounding
Safety grounding is to connect the shell of the high-voltage equipment to the earth. First, it prevents the accumulation of charge on the casing, which generates electrostatic discharge and endangers the safety of equipment and personnel. For example, the grounding of the computer case and the tail of the tanker truck dragging on the ground are all to release the accumulated charge and prevent accidents. Second, when the insulation of the equipment is damaged and the casing is charged, the power supply protection action is prompted to cut off the power supply to protect the safety of the staff, such as the casing of the refrigerator and rice cooker. Third, it can shield the huge electric field of the equipment and play a protective role, such as the guardrail of the civil transformer.
2. Lightning protection grounding
When power electronic equipment is struck by lightning, whether it is direct lightning or induction lightning, if there is no corresponding protection, the power electronic equipment will be greatly damaged or even scrapped. To prevent lightning strikes, we generally set lightning rods at high places (such as roofs and chimney tops) and connect them to the ground to prevent lightning strikes from endangering the safety of equipment and personnel. Safety grounding and lightning protection grounding are both to provide safe protection measures for electronic power equipment or personnel to protect the safety of equipment and personnel.
3. Working grounding
Working grounding is a reference potential provided for the normal operation of the circuit. This reference potential is generally set to zero. The reference potential can be set to a certain point, a certain section or a certain block in the circuit system. When the reference potential is not connected to the ground, it is regarded as a relative zero potential. However, this relative zero potential is unstable. It will change with the change of the external electromagnetic field, causing the system parameters to change, resulting in unstable operation of the circuit system. When the reference potential is connected to the ground, the reference potential is regarded as the zero potential of the ground, and will not change with the change of the external electromagnetic field. However, unreasonable working grounding will increase the interference of the circuit. For example, the interference caused by incorrect grounding points and the interference caused by the common end of electronic equipment not being properly connected. In order to effectively control the various interferences generated by the circuit during work and make it meet the electromagnetic compatibility principle. When we design the circuit, according to the nature of the circuit, we can divide the working ground into different types, such as DC ground, AC ground, digital ground, analog ground, signal ground, power ground, power supply ground, etc. Different grounds should be set separately. Do not mix them together in one circuit. For example, the digital ground and the analog ground cannot share a ground wire, otherwise the two circuits will generate very strong interference and paralyze the circuit!
4. Signal grounding
The signal ground is the common reference ground wire of the zero potential of various physical quantity signal sources. Since the signal is generally weak and susceptible to interference, unreasonable grounding will cause interference in the circuit, so the requirements for the signal ground are high.
5. Analog ground
The analog ground is the common reference ground wire of the zero potential of the analog circuit. There are small signal amplifier circuits, multi-stage amplifiers, rectifier circuits, voltage regulator circuits, etc. in the analog circuit. Improper grounding will cause interference and affect the normal operation of the circuit. The grounding in the analog circuit is of great significance to the entire circuit. It is one of the foundations for the normal operation of the entire circuit. Therefore, the role of reasonable grounding in the analog circuit on the entire circuit cannot be ignored.
6. Digital ground
The digital ground is the common reference ground wire of the zero potential of the digital circuit. Since the digital circuit works in a pulse state, especially when the leading and trailing edges of the pulse are steep or the frequency is high, a large number of electromagnetic waves will interfere with the circuit. If the grounding is unreasonable, the interference will be aggravated, so the selection of the grounding point of the digital ground and the laying of the grounding wire should also be fully considered.
7. Power ground
The power ground is the common reference ground line of the power supply zero potential. Since the power supply often supplies power to various units in the system at the same time, and the power supply properties and parameters required by each unit may be very different, it is necessary to ensure the stable and reliable operation of the power supply and other units. The power ground is generally the negative pole of the power supply.
8. Power ground
The power ground is the common reference ground wire of the zero potential of the load circuit or power drive circuit. Since the current of the load circuit or power drive circuit is strong and the voltage is high, if the ground wire resistance is large, a significant voltage drop will be generated and a large interference will be generated, so the interference on the power ground wire is large. Therefore, the power ground must be set separately from other weak current grounds to ensure the stable and reliable operation of the entire system.
Shielding and grounding should be used together to achieve a good shielding effect. Mainly for the sake of electromagnetic compatibility, the two typical shieldings are electrostatic shielding and alternating electric field shielding, which are introduced below:
Electrostatic shielding: When a charged conductor is surrounded by a complete metal shielding body, an equal amount of different charges as the charged conductor will be induced on the inside of the shielding body, and an equal amount of the same charge as the charged conductor will appear on the outside, so there is still an electric field on the outside. If the metal shielding body is grounded, the charges on the outside will flow into the earth, and there will be no electric field on the outside of the metal shell, which is equivalent to the electric field of the charged body in the shell being shielded.
There are two types of grounding facilities. One is working grounding, which is the grounding that connects the live parts of electrical appliances to the earth, such as the grounding of the neutral line at the low-voltage point of a three-phase transformer;
the other is protective grounding, which is the grounding to prevent the insulation layer of the electrical appliance from being damaged and causing the outer shell to be live or other non-live metal parts to be live and injure people. The grounding wire must be driven into the earth about 1.2~1.5m deep to be considered qualified grounding. The
three ends of three-phase electricity are called phase wires, and the three tails of three-phase electricity are connected together to be called the neutral wire, also called the "zero wire". The reason for calling it the zero wire is that no current passes through the neutral wire at the moment of three-phase balance, and it is directly or indirectly connected to the earth, and the voltage with the earth is also close to zero.
The ground wire is a line that reliably connects the outer shell of the equipment or electrical appliance to the earth, and is a good solution to prevent electric shock accidents.
Under normal circumstances, the live wire in the three-phase circuit uses red, yellow, and blue to represent the three live wires, and the neutral wire uses black. In a single-phase lighting circuit, yellow generally represents the live wire, blue is the neutral wire, and yellow and green are the ground wires. Some places also use red to represent the live wire, black to represent the neutral wire, and yellow and green to represent the ground wire.
Electrical appliances have neutral wires and live wires, which form a path so that current can flow through the electrical appliances and make them work. When the switch is turned off, the neutral wire is not charged. The ground wire is not charged
regardless of whether the switch is turned off or not. Its main function is the grounding you mentioned. In order to avoid leakage accidents or the harm that strong electric potential may cause to people, high-power electrical appliances have a grounding wire that can lead the excess current or strong electric potential generated into the earth through the ground wire. If
the ground wire is not connected properly, it cannot operate normally. It is a setting that exists for the safety of users.
The neutral wire is the path for alternating current to return to the generator through the electrical appliance, and the ground wire is the wire that the electrical appliance directly or indirectly connects to the real earth (generally, the grounding end should be more than 1m deep into the ground).
Since the earth is generally considered to be the lowest potential (0V), the ground wire connected to the earth can ensure that the lowest potential at both ends of the voltage of the electrical appliance is the same as the earth, so that the instruments and equipment can work more safely.
Poor grounding will cause unstable neutral voltage (not 0V) and even cause leakage to the ground, making the instrument unable to work.
The symbol of the ground wire is (EARTH) E. The symbol of the live wire is (LIVE) L, and the symbol of the neutral wire is (NEUTRAL) N.
In order to make the AC power conversion function very convenient, three sinusoidal AC wires are usually used for industrial electricity. The current phase (reflecting the direction and magnitude of the current) differs by 120 degrees from each other. Usually we call each such wire a phase wire (live wire). Usually, power transmission is in the form of three-phase four-wire. The three ends of the three-phase power are called phase wires, and the three tails of the three-phase power are connected together to call the neutral wire, also called the "zero wire". The reason for calling it the zero wire is that there is no current passing through the neutral wire at the moment of three-phase balance, and it is directly or indirectly connected to the earth, and the voltage with the earth is also close to zero. The ground wire is a line that reliably connects the outer shell of the equipment or electrical appliance to the earth, and is a good solution to prevent electric shock accidents. The live wire is also called the phase wire, which together with the neutral wire forms a power supply circuit. In the low-voltage power grid, a three-phase four-wire system is used to transmit power, in which there are three phase wires and one neutral wire. In order to ensure the safety of electricity use, the user area is changed to a three-phase five-wire power supply system. The fifth wire is the ground wire. One end of it is buried deep underground with a metal conductor near the user area, and the other end is connected to the ground wire contact of each user to play the role of grounding protection.
Universal plug:
Green/yellow: ground wire.
Blue: neutral wire.
Brown: live wire
North American plug:
Green/yellow or green: ground wire.
Blue or white: neutral wire.
Brown or black: live wire
Electricity for ground wire is divided into power and household electricity
Power electricity is commonly known as 380-volt electricity, which is mostly used in factories. This kind of electricity is mostly three-phase four-wire. There are three live wires and one neutral wire in the four-wire. The live wire refers to any phase in the three-phase four-wire power grid ABC, and the neutral wire refers to the wire that has no voltage and current to the ground in the three-phase four-wire. The three live wires pass through the load such as motors and other electrical equipment and then pass through the neutral wire to form a loop, so that the equipment can work normally. The neutral wire is grounded in the power plant. Under normal circumstances, the live wires in the three-phase circuit are represented by red, yellow, and blue colors, and the neutral wire is black.
Household electricity refers to the 220-volt electricity we often say, also called single-phase electricity, with two wires, one live wire and one neutral wire. The live wire passes through loads such as light bulbs and other electrical appliances and then forms a loop through the neutral wire, so that the electrical appliances can work normally. The neutral wire here is also grounded in the power plant. In a single-phase lighting circuit, yellow generally represents the live wire, blue is the neutral wire, and yellow and green are the ground wires. Some places also use red to represent the live wire, black to represent the neutral wire, and yellow and green to represent the ground wire. Generally speaking, red is the live wire, blue is the neutral wire, and black is the ground wire.
Although the neutral wires of power and household electricity are grounded in power plants, the ground wire and the neutral wire we usually talk about are not the same concept. Look at the three-hole power socket in our home. If it is a formal construction, one hole is the live wire, one hole is the neutral wire, and one hole is the ground wire. The ground wire here is connected to the ground after the whole building is collected. This is what is commonly called the ground wire. Most household appliances require a ground wire, which means they must be connected to this ground wire. The live
wire is live, while the ground wire and the neutral wire are not live. There is a live wire and a neutral wire in a two-hole household socket. A test pen can be used to detect that the live wire is live and the neutral wire is not live. There is a ground wire in a three-hole socket. The ground wire must be connected to the outer casing of the appliance to prevent leakage of electricity from the appliance and cause electric shock and casualties.
In addition, there are regulations for the wiring positions of each hole in the household socket. If you disassemble the socket, you can see that the point marked with L is connected to the live wire, the point marked with N is connected to the neutral wire, and the ground wire has a special grounding symbol. People who don’t understand must not connect randomly (especially the position of the ground wire), otherwise it may cause serious consequences.
The ground wire is an equipotential body that serves as the reference point of the circuit potential. This definition does not conform to the actual situation. The potential on the actual ground wire is not constant. If you use an instrument to measure the potential between the points on the ground wire, you will find that the potential of each point on the ground wire may differ greatly. It is these potential differences that cause the abnormal operation of the circuit. The definition that the circuit is an equipotential body is only people’s expectation of the ground wire potential. Henry gave a more realistic definition of the ground wire. He defined the ground wire as a low-impedance path for the signal to flow back to the source. This definition highlights the flow of current in the ground wire. According to this definition, it is easy to understand the cause of the potential difference in the ground wire. Because the impedance of the ground wire is never zero, when a current passes through a finite impedance, a voltage drop will occur. Therefore, we should imagine the potential on the ground wire as waves in the sea, rising and falling.
At present, most of the power sockets we use are single-phase three-wire sockets or single-phase two-wire sockets. In a single-phase three-wire socket, the middle is the ground wire, which is also used for positioning. The other two ends are connected to the live wire and the neutral wire respectively. The wiring order is left zero and right live, that is, the left is the neutral wire and the right is the live wire. All household appliances with metal shells use single-phase three-wire power plugs. The three plugs are arranged in an equilateral triangle, and the longest and thickest copper plug on the top is the ground wire. The two below the ground wire are the live wire (the letter "L" Live Wire) and the line (the letter "N" Naughtwire), and the order is left zero and right live (when the back of the plug faces yourself).
The ground wire is short-circuited to the earth through a deeply buried electrode. The transmission of municipal electricity is in a three-phase mode, and there is a neutral wire. When the three phases are balanced, the current of the neutral wire is zero, commonly known as the "neutral wire". Another feature of the neutral wire is that it is short-circuited with the ground wire at the system's total power distribution input, and the voltage difference is close to zero. The three phases of three-phase electricity and the neutral line have a voltage of 220, which can cause electric shock to people. It is commonly known as the "live wire".
The difference between the neutral line and the ground line
1. The neutral line and the ground line are different concepts and are not the same thing.
2. The ground line has a zero potential to the ground. The nearest point of the electrical appliance in use is grounded.
3. The neutral line's potential to the ground is not necessarily zero. The nearest grounding point of the neutral line is at the substation or the power transformer.
4. Sometimes the neutral line can shock people. When will it happen? When your electric stove does not heat up, don't think that there is no electricity and it will not shock people. Wrong! There may be such a possibility that the N line is disconnected far away from your electrical appliance. If you measure it with a voltmeter, you will find that the LN line of the electrical appliance is the voltage of the mains!
5. The ground line will not shock people, unless it is a very bad situation, the designer does not understand, or messes up the product!
6. If there is a neutral line and a ground line in your circuit, you will find that there is a high-voltage capacitor between them.
The so-called ground wire is a wire used to lead current into the earth. When electrical equipment leaks electricity or the voltage is too high, the current enters the earth through the ground wire.
Classification of ground wires
(1) Power supply ground wire: It is connected to the neutral point of the transformer and then leads to the main line. According to the standard, it is grounded every 20-30 meters to play a safety protection role in the circuit. In the case of leakage, the user and the ground wire form a parallel circuit. With the ground wire, the current will flow into the earth quickly due to the relatively small resistance of the ground wire, and the user can avoid electric shock. In practice, it is usually a yellow-green wire.
The ground wire is very important in household electricity use, but there is no ground wire in the power supply network in some areas. The following method can be used to remedy this. Find a place outside the house, take a 50-70mm wide and 1-2 meter long angle iron and drive it into the ground, then connect the ground wire to the angle iron. It is best to use bolts to fix the connection. The connecting wire should be as thick as possible, 6-10 square millimeters. To further reduce the grounding resistance, you can pour some salt water around the angle iron.
(2) Circuit ground: When designing a circuit, the main purpose is to prevent interference and improve the radiation efficiency of radio waves. The ground wire is widely used as a reference point for potential, providing a reference potential for the entire circuit. At this time, the ground wire may not be connected to the real earth, but is often connected to one of the input power lines (usually the neutral line), and its potential is also unrelated to the earth potential. When designing the entire circuit, the voltage on the ground wire is 0V to unify the potential of the entire circuit.
Ground plug
The longer of the three pins is grounded and can be called the grounding pin. The other two shorter pins are used to connect household appliances to the circuit and can be called conductive pins. When designing the power plug, in order to consider the safety of the user, the grounding pin is consciously designed to be several millimeters longer than the conductive pin. This is because when inserting a three-pin plug, the grounding pin first contacts the grounding wire in the socket, so that grounding protection can be formed first, and then the power is turned on; conversely, when unplugging the three-pin plug, the conductive pin is first separated from the conductive end in the power socket, and then disconnected after the grounding pin. If the metal shell of a household appliance is charged due to damage to the insulator, the grounding pin will form a ground short-circuit current, so that the metal shell of the household appliance is grounded and discharged to the ground, so that people will not be electrocuted, which plays a role in safety protection.
The symbol of the ground wire is E (Earth). The corresponding live wire symbol is L, and the neutral wire symbol is N.
The ground wire symbol
"Grounding" is an important symbol in the circuit diagram. It involves several concepts that are both related and different, such as "signal ground", "connecting to the casing", "protective grounding", "equipotential", etc., and the differences between them must be noted when drawing and reading electrical drawings.
1. Signal ground
"Signal ground" is also called "general grounding" or "grounding", which refers to the common reference potential of all circuits during signal transmission. In the circuit, zero potential is often used as the reference potential. The symbol of "signal ground" is shown in Figure 7-6 (A).
2. Connecting to the casing
"Connecting to the casing" refers to the potential of the metal shell of the electrical equipment. The potential of the casing is often the common reference potential of the circuit in electronic equipment, so it is often called "casing ground".
3. Equipotential When
the potentials of some local common points in the circuit are equal, and these common points are different from the "signal ground", the "equipotential" symbol is used to represent these points. If there are multiple circuits in the electronic circuit diagram that refer to the same potential value (such as +2V), these points can be connected with a line when drawing, and then the potential value can be noted. This drawing method will make the connection long and tortuous, affecting the drawing and reading. If the equipotential symbol is used to represent the equal relationship of the potential at different equipotential points, the long connection line can be omitted, and the readability of the circuit diagram can be increased.
In an electronic system where analog circuits and digital circuits coexist, in order to prevent mutual interference between the two circuits caused by the ground wire, it is often required that the "signal ground" (AGND) of the analog circuit and the "signal ground" (DGND) of the digital circuit be separated inside the system, and then gathered together at the system's power supply "ground" terminal. At this time, the "AGND" and "DGND" in the circuit diagram are represented by "equipotential" symbols respectively.
How to connect the ground wire
How to connect the ground wire? The ground wire is divided into two steps: 1. The three-pin socket is assigned with a ground wire, the left is connected to the neutral wire, the right is connected to the phase (live) wire, and the reliable metal shell of the washing machine, refrigerator, etc. is also connected to the ground wire. 2. The ground wire is grounded, and metal objects such as steel pipes and angle steels are buried in the earth. The specific selection is based on the resistance value of the earth, and then connected to the distribution box with wires, and then distributed to each socket.
Introduction to ground wires
Household electrical appliances have a certain amount of static electricity on their shells due to poor insulation performance or humid use environment, which may cause electric shock accidents in severe cases. In order to avoid accidents, a wire can be connected to the metal shell of the appliance, and the other end of the wire can be connected to the ground. Once the appliance leaks electricity, the ground wire will bring the static electricity into the ground and release it. In addition, when electrical maintenance personnel use electric soldering irons to solder circuits, sometimes the electric soldering irons are charged and break down and damage the integrated circuits in the appliance. This is more important. Friends who use computers sometimes ignore the grounding of the main shell. In fact, connecting a ground wire to the computer main shell can prevent the occurrence of freezes to a certain extent.
In the power system, the grounding wire is an important tool to ensure the safety of the staff when voltage unexpectedly appears on the equipment and lines that have been powered off. According to regulations, the grounding wire must be made of bare copper soft wire with a diameter of 25mm2 or more.
In electrical appliances, the grounding wire is a line connected to the outer shell of the electrical equipment and other parts to promptly conduct unsafe charges or leakage currents generated due to various reasons.
Overview of high-voltage grounding wire:
(1) Function of high-voltage grounding wire: High-voltage grounding wire is used in line and substation construction to prevent electrostatic induction of nearby charged bodies to ensure safety when closing the switch or making mistakes.
(2) Structure of high-voltage grounding wire: The portable high-voltage grounding wire consists of an insulated operating rod, a wire clamp, a short-circuit line, a grounding wire, a grounding terminal, a busbar clamp, and a grounding clamp.
(3) High-voltage grounding wire manufacturing process: Shijiazhuang Kerui Electric Co., Ltd. specializes in the production of grounding wires with excellent manufacturing process - the conductor clamp and grounding clamp are made of high-quality aluminum alloy die-casting; the operating rod is made of epoxy resin colored tube, which has good insulation performance, high strength, light weight, bright color and smooth appearance; the grounding soft copper wire is made of multiple strands of high-quality soft copper wires, and is covered with a soft, high-temperature resistant transparent insulating sheath to prevent wear on the grounding copper wire during use. The copper wire meets the fatigue test requirements to ensure the safety of operators during operation.
Classification of high-voltage grounding wires:
(1) High-voltage grounding wires can be divided into indoor busbar type grounding wires (JDX-NL) and outdoor line type grounding wires (JDX-WS) according to the use environment.
(2) High-voltage grounding wires can be divided into 10KV grounding wires, 35KV high-voltage grounding wires, 110KV grounding wires, 220KV high-voltage grounding wires, and 500KV high-voltage grounding wires according to voltage levels.
Technical parameters of high-voltage grounding wire:
(1) 10KV high-voltage grounding wire insulation rod length: 700mm handshake part length: 300mm metal joint part length: 50mm number of sections: 1 rod diameter: 30mm total length (excluding wire clamp): 1050mm.
(2) Nominal cross-section of 35KV grounding wire: 25mm2 Total number of roots: 810 Average diameter (mm): 0.2mm Calculated cross-section: (mm2): 25.43 Length of metal joint part: 50 mm Number of sections: 1 Rod diameter: 30mm
(3) Nominal cross-section of 110KV high-voltage grounding wire: 35mm2 Total number of roots: 1136 Average diameter (mm): 0.2mm Calculated cross-section: (mm2): 35.67 Length of insulating rod part: 1360 mm Length of handshake part: 700 mm Length of metal joint part: 140 mm Number of sections: 2 Rod diameter: 30mm Total length (excluding wire clamp): 2200 mm
How to connect high-voltage grounding wire
(1) When hanging the grounding wire: first connect the grounding clamp, then connect the electrical clamp; when removing the grounding wire, you must follow the procedure to remove the electrical clamp first and then the grounding clamp.
(2) Installation: Fix the double-eye copper nose of the grounding soft copper wire on the corresponding position of the power clamp on the grounding rod (the power clamp is available in fixed and movable types), and fix the single-eye copper nose on the grounding wire on the grounding clamp or ground pin to form a complete set of grounding wires.
(3) Verify whether the voltage level of the grounding rod is consistent with the voltage level of the operating equipment.
(4) The grounding soft copper wire is available in split-phase and combined types, and the grounding rod has flat-mouth and double-spring hook type wire clamps.
How to connect the computer ground wire
The main function of the ground wire is to eliminate static electricity. If it is not connected, the display screen and the host case are prone to carry a lot of static electricity.
Generally, the three-way power switch of the building is equipped with a ground wire. You only need to pay attention to the three-way plug connected to the computer.
However, some bungalows do not have a three-way power switch, but they do not have the ability to conduct static electricity. Therefore, you need to connect a wire to the screw on the back of the chassis, and the other end of the wire is placed on the ground or inserted into the soil. This method is used to conduct static electricity. The effect is obvious, but it is a method after all, and it will not completely conduct static electricity.
A voltage-limited time-based circuit ground wire charged detection interface for an electric water heater control chip belongs to the application field of detection technology. It includes a ground wire charged detection circuit. Its characteristic is that the time-based circuit ground wire charged detection circuit is composed of a transformer, a voltage-regulating circuit and a time-based circuit. The transformer is connected to the zero ground wire and is connected to the input end of the time-based circuit through a rectifying circuit. The output end of the time-based circuit is connected to the input end of a single-chip microcomputer in the electric water heater control device, and together with the single-chip microcomputer detection program, it forms a voltage-limited time-based circuit ground wire charged detection interface. Its beneficial effect is to overcome the lack of a ground wire charged detection interface in the original electric water heater control device, and it is impossible to cut off the power supply of the electric heating tube used by the electric water heater in real time through the single-chip microcomputer control device when the ground wire is charged, which causes infringement on the personal safety of the user.
Reasons for ground wire charged
This problem is still quite troublesome, because there are many situations that cause PE to be charged.
For example, the N line and PE line are shared; the N line and PE line are connected in reverse; the equipment leakage causes the phase line and the ground line to short-circuit; the earth is not at the same potential, and if your ground line is connected to the earth in different places, it will cause a potential difference. There are also interference problems such as high frequency interference sources; finally, there is a large current flowing near the PE line, and some stray currents will be transmitted to the PE line through the earth.
|
提升卡
变色卡
千斤顶
京公网安备 11010802033920号
