The role of the line
The main function of the ground wire is that when the electrical appliance fails, the power supply may break down (or: destroy) some components, so that the housing of the electrical appliance is charged. Grounding the housing of the electrical appliance can make the leakage protection device
1. Signal “ground”;
The signal "ground", also known as the reference "ground", is the reference point of zero potential, and it is also the common segment that constitutes the circuit signal loop, with the graphic symbol "⊥".
1) DC ground: DC circuit "ground", zero potential reference point.
2) AC ground: the neutral line of AC power. should be distinguished from the ground wire.
3) Power ground: the zero-potential reference point for high-current network devices and power amplifier devices.
4) Analog ground: the zero-potential reference point of amplifier, sample-and-hold, A/D converter and comparator.
5) Digital ground: Also called logic ground, it is the zero-potential reference point of digital circuits.
6) "Hot ground": The switching power supply does not need to use a transformer, and the "ground" of its switching circuit is related to the mains grid, which is the so-called "hot ground", which is charged, and the graphic symbol is: "".
7) "Cold ground": Because the high-frequency transformer of the switching power supply isolates the input and output terminals; and because its feedback circuit is often photocoupled, it can not only transmit the feedback signal but also isolate the "ground" of both sides; so the ground of the output terminal is called For "cold ground", it is not charged. The graphic symbol is "⊥".
2. To protect the "land";
Protection "ground" is a wiring method set up to protect personnel safety. One end of the protection "ground" wire is connected to the electrical appliance, and the other end is reliably connected to the earth.
3. The "ground" in sound.
1) Shielded wire grounding: In order to prevent interference, the audio system uses a wire to connect the metal casing to the signal "ground", which is called shielding grounding.
2) Audio-specific "ground": In order to prevent interference, professional audio needs to be connected to the audio-specific "ground" in addition to shielding the "ground". This grounding device should be specially buried, and should be connected with the corresponding grounding terminal of the isolation transformer and the shielded stabilized power supply as a dedicated audio grounding point in the sound control room.
How to deal with different ground wires
1. The digital ground and the analog ground should be separated;
In demanding circuits, the digital ground should be separated from the analog ground. Even for A/D and D/A converters, the two "grounds" on the same chip should be separated, and the two "grounds" should be connected only at one point of the system.
2. Floating and grounding;
System floating is to float the ground wires of each part of the system circuit and not connect to the ground. This connection method has a certain anti-interference ability. However, the insulation resistance between the system and the ground should not be less than 50MΩ. Once the insulation performance declines, it will cause interference. Usually, the system is floating and the chassis is grounded, which can enhance the anti-interference ability and make it safe and reliable.
3. One point grounding;
In low frequency circuits, there is not much influence between wiring and components. Usually a circuit with a frequency less than 1MHz is grounded at one point.
4. Multi-point grounding.
In high frequency circuits, the influence of parasitic capacitance and inductance is greater. Generally, for circuits with frequencies greater than 10MHz, the use of multi-point grounding should not only carry out the correct grounding design and installation, but also correctly carry out grounding processing of various signals. In the control system, there are roughly the following ground wires:
(1) Digital ground: Also called logical ground, it is the zero potential of various switching (digital) signals.
(2) Analog ground: It is the zero potential of various analog signals.
(3) Signal ground: usually the ground of the sensor.
(4) AC ground: the ground wire of the AC power supply, which is usually the ground that generates noise.
(5) DC ground: the ground of the DC power supply.
(6) Shielding ground: Also called chassis ground, it is designed 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 thoughts on grounding issues:
(1) The control system should be grounded at one point. In general, 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. However, the interference of the loop formed by grounding has a great influence. Therefore, one point is often used as the grounding point; but one point grounding is not suitable for high frequency, because high frequency When , there is inductance on the ground wire, which increases the impedance of the ground wire, and at the same time, inductive coupling occurs between the wires. Generally speaking, when the frequency is below 1MHz, one-point grounding can be used; when the frequency is higher than 10MHz, multiple-point grounding can be used; between 1-10MHz, one-point grounding can be used, or multiple-point grounding can be used.
(2) AC ground and signal ground cannot be shared. Since there will be several mV or even several V voltages between two points of a power ground wire, this is a very important interference for low-level signal circuits, so it must be isolated and prevented.
(3) Comparison of floating and grounding. The whole machine is floating, that is, all parts of the system and the ground are floating. This method is simple, but the insulation resistance of the entire system and the ground should not be less than 50MΩ. This method has a certain anti-interference ability, but once the insulation drops, it will bring interference. Another way is to ground the case and leave the rest floating. This method has strong anti-interference ability and is safe and reliable, but it is complicated to implement.
(4) Analog ground. The connection method of the analog ground is very important. In order to improve the anti-common mode interference ability, the shielded floating technology can be used for the analog signal. The grounding treatment for specific analog signals should be designed in strict accordance with the requirements in the operation manual.
(5) Shield ground. In the control system, in order to reduce the capacitively coupled noise in the signal and accurately detect and control it, it is necessary to use shielding measures for the signal. Depending on the purpose of shielding, the connection method of the shielding ground is also different. The electric field shielding solves the problem of distributed capacitance, which is generally connected to the ground; the electromagnetic field shielding mainly avoids the radiation interference of high-frequency electromagnetic fields such as radar and radio. It is made of low-resistance metal material 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. The shielding method is to use high magnetic permeability materials to close the magnetic circuit, 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 source of noise interference. When a circuit has an ungrounded signal source connected to a grounded amplifier in the system, the shield of the input should be connected to the amplifier's common; conversely, when the grounded signal source is connected to an ungrounded amplifier in the system, the amplifier's input The terminal should also be connected to the common terminal of the signal source.
For the grounding of the electrical system, it should be classified according to the requirements and purposes of grounding. Different types of grounding cannot be simply and arbitrarily connected together, but should be divided into several independent grounding subsystems, each of which has its common grounding point. Or the grounding trunk line, and finally connect them together to implement the general grounding.
Second, the difference between the ground wire and the neutral wire
We know that when installing electrical appliances, first use an electric pen to distinguish the live wire and the neutral wire. If there are only two entry lines, one is the live line and the other is the zero line, when distinguishing, the human body should not have any direct contact with the earth, hold the electric pen with one hand, and cannot touch the metal part of the pen tip, but the finger should touch the end of the pen touch the metal parts of the two wires respectively, if only one can make the neon bulb of the electric pen glow, then this is the live wire. If neither of these can make the neon bulb of the pen glow, it may be that the metal part is not touched or the power supply is not connected, or the pen is broken, or the finger is not touching the metal part of the pen tail. If both can make the neon bulb glow, the neutral line is disconnected.
The detailed difference between ground wire and neutral wire
1. The zero line and the ground line are different concepts and are not the same thing. Do not interchange or mix them.
2. The ground potential of the ground wire is zero, which is the nearest ground.
3. The ground potential of the neutral line is not necessarily zero. The neutral line is grounded at the nearest substation, and there may be a certain potential difference with the local ground.
4. The zero line sometimes electrifies people. When the live wire is powered, but the device does not work, it may be that the neutral wire is broken. The neutral wire from the breakpoint near the end of the device is powered by 220V, the same as the live wire.
How to distinguish between neutral and ground
1. Wiring standard: red, yellow and green neutral wire (N) must be used for the color of the live wire (L), black and blue must be used for the ground wire (PE) color must be yellow and green. , right fire, middle ground
2. Install a leakage 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 leakage circuit breaker operates, it means the ground wire, otherwise it is the neutral wire. Pay attention to safety during testing, there may be Little Spark, you have to prepare in your heart, don't be startled!
3. If it is at home: 1. Power on and test with an electric pen, all the lights that will light up are the live wires. 2. Disconnect the neutral wire at the main switch, connect only the live wire, turn on the lights in the home, and use an electric pen to test. 3. The rest that is not bright is the ground wire.
The easiest way is to take a 220V light bulb, use an electric pen to determine the live wire, and connect two wires and a live wire to the lamp head respectively. From the brightness, you can distinguish between zero and ground. The bright one is zero, and the slightly darker one is ground.
4. Use the multimeter to put the multimeter in the AC gear of 500v, pinch one test lead, and the other test lead to touch the power line respectively. The one with high voltage is the live line, the one with low voltage is the zero line, and the one with a voltage of 0 is the ground line. The zero line-to-ground resistance is less than 4 ohms for reliable grounding. Use a multimeter to place the AC gear at 250v to measure the voltage difference between the live wire and the neutral wire, the live wire and the ground wire. The difference between the two values is less than 5v, which is a reliable grounding.
Consequences of wrong connection of ground wire and neutral wire
1. Because it is alternating current, the exchange of fire and zero has no effect on electrical appliances. In the face of the 3-hole socket, the left zero and the right fire are mainly used for maintenance. Best not to change it.
2. The zero-sum ground is reversed or mixed. This is usually fine, but it is more dangerous. The ground wire cannot be connected to the zero wire. Otherwise, the case of the device will be charged. (Generally, the casing is almost uncharged when the equipment is normal)
3. The ground wire entering the house can be temporarily used as a zero wire (so that the meter does not turn, it is stealing electricity), but if you want to use it for a long time, there are many unfavorable factors, such as: due to changes in the grounding point environment (thunderstorm, humidity, etc.) etc.) lead to voltage instability; the substation factors make the live line-to-ground voltage reach 380V, etc., which can cause the electrical equipment to be easily affected and seriously damaged.
3. Ground wire color
In order to make the AC power have a very convenient power conversion function, usually the power transmission is in the form of three-phase four-wire, and the three heads of the three-phase power are called phase wires.
The three tails of the three-phase electricity are connected together, which is called the neutral wire, also called the "neutral wire". The reason why it is called the neutral line is that there is no current passing through the neutral line at the time of three-phase balance, and it is directly or indirectly connected to the ground, and the voltage with the ground is also close to zero.
The ground wire is a line that reliably connects the casing of the equipment or electrical appliance to the ground, and is a good solution to prevent electric shock accidents. Under normal circumstances, the live wire in a three-phase circuit uses three colors of red, yellow, and blue to represent the three live wires, and the neutral wire uses black. In a single-phase lighting circuit, generally yellow is the live wire, blue is the neutral wire, and yellow and green are the ground wire. In some places, red is used for the live wire, black for the neutral wire, and yellow and green for the ground wire.
Distinguishing colors and functions of live wire, neutral wire and ground wire
In the country identification of the power cord, the general phase line is yellow for phase A, green for phase B, and red for phase C. Zero line – light blue. The ground wire is green and yellow. If it is a three-phase socket, the left is the neutral wire, the middle (above) is the ground wire, and the right is the live wire.
Generally, 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 electricity consumption, it is divided into power consumption and household electricity. Power consumption is often referred to as 380-volt electricity, which is mostly used in factories and some large electrical equipment such as 5P air conditioners and hotel smoking machines. This kind of electricity is mostly three-phase four-wire. There are three live wires and one neutral wire in the four wires. The live wire refers to any phase in the three-phase four-wire power grid ABC, and the neutral wire refers to the three-phase four-wire to ground without voltage and current The one wire, the three live wires pass through the load such as the motor and other electrical equipment, and all pass through the neutral wire to form a loop, and the equipment can work normally. The neutral wire is grounded at the power plant. Under normal circumstances, the live wire in a three-phase circuit uses three colors of red, yellow and blue to represent the three live wires, and the neutral wire uses black or blue.
Household electricity refers to what we often call 220-volt electricity, also called single-phase electricity, with two wires, a live wire and a neutral wire. After the live wire passes through the load such as light bulbs and other electrical appliances, it forms a loop through the neutral wire, so that the electrical appliances can work normally. The neutral wire here is also grounded at the power plant. In a single-phase lighting circuit, generally yellow, green, red, white, gray, and brown indicate the live wire, light blue and blue are the neutral wire, and the yellow-green and black wires are the ground wire.
Although the neutral lines of power and household electricity are grounded in power plants, the ground and neutral lines we usually talk about are not the same concept. Look at the three-hole power socket in our house. If it is a regular construction, one of the holes is the live wire, the other is the neutral wire, and the other is the ground wire. The ground wire here is grounded after the entire building is brought together, which is often referred to as the ground wire. Most household appliances require a ground wire, which is to be connected with this ground wire. Generally, the neutral line passes through the leakage switch and the ground line cannot. The ground potential of the ground wire is zero, and the nearest point of the electrical appliance used is grounded; the ground potential of the zero wire is not necessarily zero, and the nearest ground point of the zero wire is at the transformer substation or power supply; Electric people, such as electric stoves are not hot, don't think that there is no electricity, you will not be able to electric people, there may be such a possibility, the N line is disconnected far away from your electrical appliances, use a voltmeter to measure it. It is found that the LN line of the electrical appliance is the voltage of the mains; the ground wire will not power people, unless it is very bad or the installer does not understand or mess around. In some circuits with neutral and ground, you will find a high voltage capacitor between them.
The live wire is live, but the ground wire and the neutral wire are not. There is a live wire and a neutral wire in the socket of the two jacks in the household. The live wire can be measured with an electric pen, and the neutral wire is not charged. There is only a ground wire in the socket of the three jacks, and the ground wire should be connected to the shell of the electrical appliance to prevent electric shock from electrical leakage and casualties. The point marked with L is connected to the live wire, the point marked by N is connected to 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 the single-phase three-wire socket, the middle is the ground wire, which is also used for positioning; the wiring sequence is left zero and right fire. 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 above is the ground wire. The two below the ground wire are the live wire (the sign letter is "L") and the zero wire (the sign letter is "N"), and the order is left zero and right fire, (when the back of the plug is facing yourself).
Different types of grounding and circuits with different functions have different grounding methods. Common grounding methods in electronic power equipment are as follows:
1. Safety grounding
Safety grounding means connecting the enclosure of high-voltage equipment to the earth. The first is to prevent the accumulation of electric charges on the casing, resulting in electrostatic discharge and endangering equipment and personal safety. For example, the grounding of the computer case and the tail of the fuel tanker are all to release the accumulated electric charges and prevent accidents. ; Second, when the insulation of the equipment is damaged and the casing is charged, the protective action of the power supply is prompted to cut off the power supply, so as to protect the safety of the staff, such as the casings of refrigerators and rice cookers. The third is to shield the huge electric field of the equipment and play a protective role, such as the protective fence of civil transformers.
2. Lightning protection grounding
When the power electronic equipment is struck by lightning, whether it is a direct lightning strike or an induced lightning strike, if there is no corresponding protection, the power electronic equipment will be greatly damaged or even scrapped. In order to prevent lightning strikes, we generally set up lightning rods at high places (such as roofs, tops of chimneys) to connect to the ground to prevent damage to equipment and personnel during lightning strikes. Safety grounding and lightning protection grounding are both to provide safety protection measures for electronic power equipment or personnel, and to protect the safety of equipment and personnel.
3. Work grounding
The working ground 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 as a certain point, a certain segment 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. But this relative zero potential is unstable, it will change with the change of the external electromagnetic field, so that the parameters of the system will change, which will lead to the 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 work grounding will increase the interference of the circuit. For example, the interference caused by the incorrect grounding point, and the interference caused by the incorrect connection of the common end of the electronic equipment. In order to effectively control the circuit to produce various disturbances in the work, so that it can comply with the principle of electromagnetic compatibility. When designing a circuit, according to the nature of the circuit, the working ground can be divided into different types, such as DC ground, AC ground, digital ground, analog ground, signal ground, power ground, power ground, etc. Different grounds should be set separately. Do not mix them together in a circuit. For example, digital ground and analog ground cannot share the same ground wire, otherwise the two circuits will produce very strong interference and the circuit will be paralyzed!
4, signal ground
The signal ground is the common reference ground for the zero potential of various physical quantity signal sources. Because the signal is generally weak and susceptible to interference, unreasonable grounding will cause interference to the circuit, so the requirements for the signal ground are higher.
5. Simulation ground
The analog ground is the common reference ground for 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. Grounding in analog circuits is of great significance to the entire circuit, and it is one of the foundations for the normal operation of the entire circuit. Therefore, the effect 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 for the zero potential of the digital circuit. Since the digital circuit works in the pulse state, especially when the front and rear 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 for the zero potential of the power supply. Since the power supply often supplies power to each unit 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 the stable and reliable operation of other units. The power ground is generally the negative pole of the power supply.
8. Power ground
The power ground is the zero-potential common reference ground of the load circuit or the power drive circuit. Due to the strong current and high voltage of the load circuit or power drive circuit, if the resistance of the grounded ground wire is large, a significant voltage drop will be generated and large interference will occur, 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 to consider electromagnetic compatibility, two typical types of shielding are electrostatic shielding and alternating electric field shielding, which are described below:
Electrostatic shielding: When the charged conductor is surrounded by a complete metal shield, the same amount of different charges as the charged conductor will be induced on the inside of the shield, and the same amount of charge as the charged conductor will appear on the outside, so there is still an electric field on the outside. exist. If the metal shield is grounded, the charges on the outside will flow into the ground, and there will be no electric field outside the metal shell, which is equivalent to shielding the electric field of the charged body inside the shell.
There are two types of grounding facilities, one is working grounding, which is the grounding that connects the live part of the electrical appliance to the ground, such as the grounding of the neutral line of the low-voltage point of a three-phase electrical transformer;
One is the protective grounding, which is the grounding to prevent the insulation layer of the electrical appliance from being damaged and causing the shell to be charged or other metal parts that are not working with electricity to be charged. The grounding wire must be driven into the depth of the earth about 1.2~1.5m to be considered as qualified grounding.
The three heads of three-phase electricity are called phase wires, and the three tails of three-phase electricity are connected together and called neutral wire, also called "zero wire". The reason why it is called the neutral line is that there is no current passing through the neutral line at the time of three-phase balance, and it is directly or indirectly connected to the ground, and the voltage with the ground is also close to zero.
The ground wire is a line that reliably connects the casing of the equipment or electrical appliance to the ground, and is a good solution to prevent electric shock accidents.
Under normal circumstances, the live wire in a three-phase circuit uses three colors of red, yellow, and blue to represent the three live wires, and the neutral wire uses black. In a single-phase lighting circuit, generally yellow is the live wire, blue is the neutral wire, and yellow and green are the ground wire. In some places, red is used for the live wire, black for the neutral wire, and yellow and green for the ground wire.
Electrical appliances have a neutral wire and a live wire, thus forming a path, so that the electrical appliance can have current to pass through and play a role. When the switch is closed, the neutral wire is not charged.
The ground wire is not charged whether the switch is turned off or not, and its main function is the grounding you mentioned. In order to avoid the occurrence of leakage accidents or the possible harm of strong electric potential to people, high-power electrical appliances have a grounding wire, which can lead the excess current or strong electric potential to the earth through the grounding wire.
If the ground wire is not connected properly, it will not work properly. It is a setting that exists for the safety of users.
The neutral wire is the passage of AC power returning 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 ground end should be deeper than 1m 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 across the voltage of the electrical appliance is the same as the earth, so that the instruments and equipment work relatively safely.
Poor grounding will cause the zero line voltage to be unstable (not 0V), or even cause leakage to the ground, making the instrument unable to work.
Fourth, the ground mark
The sign of the ground wire is (English EARTH) E. The sign of the live line is (English LIVE) L, and the sign of the zero line is (English NEUTRAL) N.
In order to make the alternating current have a very convenient power conversion function, usually industrial electricity, three sinusoidal alternating current. The current phases (reflecting the direction and magnitude of the current) are 120 degrees apart from each other. Usually we call each such wire as a phase wire (live wire). Usually power transmission is in the form of three-phase four-wire. The three heads of three-phase electricity are called phase wires, and the three tails of three-phase electricity are connected together. The neutral wire is also called the "neutral wire". The reason why it is called the neutral line is that there is no current passing through the neutral line at the time of three-phase balance, and it is directly or indirectly connected to the ground, and the voltage with the ground is also close to zero. The ground wire is a line that reliably connects the casing of the equipment or electrical appliances to the ground, 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, power is transmitted in a three-phase four-wire system, in which there are three phase wires and one neutral wire. In order to ensure the safety of electricity use, the three-phase five-wire system is used for power supply in the user area. The fifth wire is the ground wire. One end of it is buried in the ground with a metal conductor near the user area, and the other end is connected to each user. The grounding point of the cable is connected to the grounding point, which plays the role of grounding protection.
Green/Yellow: Ground wire.
Blue: neutral line.
North American Plug:
Green/Yellow or Green: Ground wire.
Blue or White: Neutral.
Brown or Black: FireWire
Ground wire electricity is divided into power electricity and household electricity
Power electricity is what is often called 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 wires. The live wire refers to any phase in the three-phase four-wire power grid ABC. , The neutral line refers to the one wire that has no voltage and current with three-phase four-wire to the ground. After the three live wires pass through the load such as the motor and other electrical equipment, they all pass through the neutral line to form a loop, and the equipment can work normally. Grounded. Generally, the live wire in a three-phase circuit uses three colors of red, yellow, and blue to represent the three live wires, and the neutral wire uses black.
Household electricity refers to what we often call 220-volt electricity, also called single-phase electricity. Normal work. The neutral wire here is also grounded in the power plant. In a single-phase lighting circuit, generally yellow means the live wire, blue is the neutral wire, and the yellow-green is the ground wire. In some places, red is used for the live wire, black for the neutral wire, and yellow and green for the ground wire. In general, red is the live wire, blue is the neutral wire, and black is the ground wire.
Although the neutral line of power and household electricity is grounded in power plants, the ground line and neutral line we usually talk about are not the same concept. Look at the three-hole power socket in our home, if it is a regular construction, one of the holes It is the live wire, one hole is the neutral wire, and the other is the ground wire. The ground wire here is grounded after the whole building is collected. This is the ground wire that is often said. Most household appliances require a ground wire, which is to be connected to this ground. wire together.
The live wire is live, but the ground wire and the neutral wire are not. There is a live wire and a neutral wire in the socket of the household two jacks. You can use an electric pen to detect that the live wire is charged, and the neutral wire is not charged. There is only a ground wire in the socket of the three jacks, and the ground wire should be connected to the shell of the electrical appliance to prevent electric shock from electrical leakage and casualties.
In addition, the wiring position of each hole in the household socket is stipulated. If you disassemble the socket, you can see that the point marked with L is connected to the live wire, the point marked by N is connected to the neutral wire, and the ground wire has a special ground. symbol. People who don't understand must connect them indiscriminately (especially the location 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 is not in line with the actual situation. The potential on the actual ground wire is not constant. If you use a meter to measure the potential between the points on the ground line, you will find that the potential of each point on the ground line may vary greatly. It is these potential differences that cause the abnormal operation of the circuit. The definition of a circuit being an equipotential body is only one's expectation of the ground potential. HENRY gave a more realistic definition of the ground wire, he defined the ground wire as: the low impedance path for the signal to flow back to the source. The flow of current in the ground wire is highlighted in this definition. 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 flows through a finite impedance, a voltage drop occurs. Therefore, we should imagine that the potential on the ground wire is like waves in the sea, one after another.
At present, most of the power sockets we use are single-phase three-wire sockets or single-phase two-wire sockets. In the single-phase three-wire socket, the middle is the ground wire, which is also used for positioning, and the other two ends are connected to the live wire and the neutral wire respectively. All electrical appliances use single-phase three-wire power plugs. The three plugs are arranged in an equilateral triangle, and the longest and thickest copper plug above is the ground wire. The two below the ground wire are the live wire (the symbol letter is "L" Live Wire) (the symbol letter is "N" Naughtwire), the order is left zero and right fire, (when the back of the plug is facing yourself).
The ground wire is short-circuited to the ground through a deeply buried electrode. The transmission of mains is in a three-phase way, and there is a neutral line. When the three-phase balance is in place, the current of the neutral line is zero, commonly known as "neutral line". The electrical input is shorted and the voltage difference is close to zero. The three phase wires of three-phase electricity and the neutral wire have a voltage of 220, which will cause electric shock to people, commonly known as "fire wire".
The difference between neutral and ground
1. The zero line and the ground line are different concepts, not the same thing.
2. The ground potential of the ground wire is zero. Ground the nearest point of the appliance used.
3. The ground potential of the neutral line is not necessarily zero. The nearest ground point for the neutral is at the substation or the transformer supplying it.
4. The zero line sometimes electrifies people, when? When your electric stove does not heat up, don't think that there is no electricity, it will not electrify people, it's wrong! There may be such a possibility, away from your The N line of the electrical appliance is disconnected. Using a voltmeter, you will find that the LN wire of the electrical appliance is the voltage of the mains!
5. The ground wire will not electrocute people, unless the situation is very bad, the designer does not understand, or the product is messed up!
6. If you have neutral and ground wires in your circuit, you will find a high withstand voltage capacitor between them.
5. Ground wire symbol
The so-called ground wire is a wire used to introduce current into the ground; when the electrical equipment leaks or the voltage is too high, the current enters the ground through the ground wire.
Ground wire classification
(1) Power supply ground wire: lead out the main line after the neutral point of the transformer is grounded. According to the standard, it is repeatedly grounded every 20-30 meters to play a safety protection role in the circuit. In the case of leakage, the electricity user and the ground wire form a parallel circuit. With the ground wire, since the resistance of the ground wire is relatively small, the current will flow into the ground quickly, 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, but there is no ground wire in the power supply network in some areas, which can be remedied by the following methods. Find a place outside the house, take an angle iron with a width of 50-70mm and a length of 1-2 meters and drive it into the ground, and then connect the ground wire to the angle iron. It is best to fix it with bolts when connecting, and the connecting wire should be as thick as possible. 6-10 mm2, to reduce the grounding resistance, you can pour a little more saline around the angle iron.
(2) Circuit ground wire: In circuit design, the main purpose is to prevent interference and improve the radiation efficiency of radio waves. The ground wire is widely used as a potential reference point, providing a reference potential for the entire circuit. At this time, the ground wire is not necessarily connected to the real ground, but is often connected to one of the input power wires (usually the neutral wire), and its potential is also independent of the ground potential. When the whole circuit is designed, the voltage on the ground line is 0V to unify the potential of the whole circuit.
The longer of the three feet is grounded and can be called grounding feet, and the other two shorter feet are used to connect household appliances to the circuit, and they can be called conductive feet. 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 the three-pin plug is inserted, the grounding pin contacts the ground wire in the socket first, so that the grounding protection can be formed first, and then the power supply is turned on; on the contrary, when the three-pin plug is pulled out, the conductive pin first contacts the conductive end of the power socket. Separated and disconnected after the ground pin. If the metal casing of the household appliance is charged due to the damage of the insulator, the grounding pin will form a short-circuit current to the ground, so that the metal casing of the household appliance is grounded and discharged to the ground, so that people will not be electrocuted and play a role in safety protection. .
The symbol for the ground wire is E (Earth). The corresponding live line symbol is L, and the zero line symbol is N.
"Grounding" is an important symbol in circuit diagrams. It involves several concepts that are both related and different, such as "signal ground", "connected to the chassis", "protective grounding", "equipotential", etc. The difference between electrical drawing and drawing must be noted when drawing.
"Signal ground", also known as "general ground" or "ground", refers to the common reference potential of all circuits during signal transmission. In circuits, zero potential is often used as the reference potential. The "signal ground" symbol is shown in Figure 7-6(A).
2. Connect the case
"Enclosure" refers to the potential at which the metal casing of electrical equipment is located. The potential of the chassis is often the common reference potential of the circuit in electronic equipment, so it is often called "chassis ground".
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. In the electronic circuit diagram, if there are multiple circuits 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 indicated. This drawing method will make the connection line long and zigzag, which will affect drawing and reading. If the equipotential symbols are used at different equipotential places to represent the equal relationship of potentials, the long connection lines can be omitted and the readability of the circuit diagram can be increased.
In an electronic system where analog circuits and digital circuits exist at the same time, in order to prevent mutual interference between the two circuits caused by the ground wire, the "signal ground" (AGND) of the analog circuit and the "signal ground" (DGND) of the digital circuit are often required. ) are separated inside the system, and then brought together at the "ground" terminal of the power supply of the system. At this time, "AGND" and "DGND" in the circuit diagram are respectively represented by "equipotential" symbols.
6. How to connect the ground wire
How to connect the ground wire? The ground wire is divided into two steps: 1. The three-eye socket is assigned the ground wire, the left wire is connected to the neutral wire, and the right wire is connected to the phase (fire) wire. The reliable metal casings of washing machines and refrigerators are also grounded. 2. The ground wire is grounded, buried in the ground with metal objects such as steel pipe and angle steel, which is selected according to the resistance value of the ground, and then connected to the distribution box with wires, and then tapped to each socket.
Introduction to Grounding Wires
Due to the poor insulation performance of household electrical equipment or the use of a humid environment, the shell will have a certain amount of static electricity, and an electric shock accident may occur in severe cases. In order to avoid accidents, you can connect a wire on the metal casing of the electrical appliance, and connect the other end of the wire to the ground. Once the electrical appliance leaks, the ground wire will bring static electricity into the ground and release it. In addition, it is more important for electrical maintenance personnel to break down and damage the integrated circuit in the electrical appliance because the electrical soldering iron is charged when using the electric soldering iron to weld the circuit. Friends who use computers sometimes ignore the grounding of the main chassis. In fact, connecting the main chassis of the computer to the ground wire can prevent the occurrence of crashes to a certain extent.
Grounding in power systems: An important tool to keep workers safe in the event of unexpected voltages appearing on equipment and lines that have been powered off. According to regulations, the grounding wire must be made of bare copper flexible wire of 25mm 2 or more.
In electrical appliances, the grounding wire is a line that is connected to the housing of electrical equipment and other parts in time to export unsafe electric charges or leakage currents caused by various reasons.
Overview of high voltage ground wire:
(1) Function of high-voltage grounding wire: The high-voltage grounding wire is used for line and substation construction to prevent electrostatic induction shock or mis-closing of nearby charged objects to ensure safety.
(2) High-voltage grounding wire structure: The portable high-voltage grounding wire consists of an insulating operating rod, a wire clip, a short-circuit wire, a grounding wire, a grounding terminal, a bus clip, and a grounding clip.
(3) Production process of high-voltage grounding wire: Shijiazhuang Kerui Electric Co., Ltd. specializes in the production of grounding wires, and the production process is excellent — the wire clip and grounding clip are made of high-quality aluminum alloy die-casting; the operating rod is made of epoxy resin color tube, which has excellent insulation performance Good, high strength, light weight, bright color, smooth appearance; grounding soft copper wire is made of multiple strands of high-quality soft copper wire, and is covered with a soft, high temperature-resistant transparent insulating sheath, which can prevent grounding copper in use. The wear and tear of the wire, the copper wire meets the fatigue test requirements, to ensure the safety of the operator in operation.
Classification of high voltage grounding wires:
(1) The high-voltage grounding wire can be divided into: indoor busbar type grounding wire (JDX-NL) and outdoor line type grounding wire (JDX-WS) according to the use environment.
(2) High-voltage grounding wires can be divided into: 10KV grounding wire, 35KV high-voltage grounding wire, 110KV grounding wire, 220KV high-voltage grounding wire, and 500KV high-voltage grounding wire according to the voltage level.
High voltage ground wire technical parameters:
(1) Length of insulating rod part of 10KV high voltage grounding wire: 700mm Length of handshaking part: 300 mm Length of metal joint part: 50 mm Number of sections: 1 Rod diameter: 30mm Total length (excluding wire clamp): 1050 mm.
(2) Nominal section of 35KV grounding wire: 25mm2 Total number: 810 Average diameter (mm): 0.2mm Calculated section: (mm2): 25.43 Length of metal joint part: 50 mm Number of sections: 1 Rod diameter: 30mm
(3) Nominal section of 110KV high-voltage grounding wire: 35mm2 Total number: 1136 Average diameter (mm): 0.2mm Calculated section: (mm2): 35.67 Length of insulating rod part: 1360 mm Length of handshaking part: 700 mm Length of metal joint part : 140 mm Number of sections: 2 Rod diameter: 30mm Overall length (excluding clamps): 2200 mm
How to connect the high voltage ground wire
(1) When hanging the grounding wire: connect the grounding clip first, and then connect the electric clip; when removing the grounding wire, the electric clip must be disassembled first, and then the grounding clip must be disassembled according to the procedure.
(2) Installation: Fix the double-eye copper nose on the grounded soft copper wire in the corresponding position of the electric connection clip on the grounding rod (the electric connection clamp has a fixed type and a movable type), and connect the single-eye copper nose on the grounding wire. Fixed on ground clips or ground pins to form a complete set of ground wires.
(3) Verify that the voltage level of the ground rod is consistent with the voltage level of the operating equipment.
(4) The grounding soft copper wire has split-phase and combined type, and the grounding rod has flat-type and double-reed hook-type clips.
How to connect the ground wire of the computer
The main function of the ground wire is to eliminate static electricity. If it is not connected, it is easy to carry a lot of static electricity such as the display screen and the main box.
Generally, the three-way electric door of the building has a ground wire, just pay attention to the power strip connected to the computer is also a three-way plug.
However, some bungalows do not have three-way switch doors, but they do not have the ability to conduct static electricity, so you need to connect a wire to the screw behind the chassis, and the other end of the wire falls to the ground or is inserted into the soil. The method to conduct static electricity is more obvious, but after all, it is a local method, and it will not completely guide the static electricity.
Seven, the ground wire is live
The utility model relates to an electric water heater control chip voltage limiting type time base circuit ground wire live detection interface, which belongs to the application field of detection technology. Including the ground wire live detection circuit. It is characterized in that the live detection circuit of the ground wire of the time base circuit is composed of a transformer, a rectifier circuit and a time base circuit. The transformer is connected to the neutral ground wire, and is connected to the input end of the time base circuit through the rectifier circuit, and the output end of the time base circuit is connected to the time base circuit. The input end of the single-chip microcomputer in the electric water heater control device is connected, and together with the single-chip detection program, it forms a voltage-limiting time-base circuit ground wire live detection interface. The beneficial effect is to overcome the lack of the ground wire live 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 control device when the ground wire is live, resulting in personal injury to the user. Security violation.
The reason why the ground wire is live
This problem is more troublesome to say, because there are many situations in which PE has electricity.
For example, the N line and the PE line are shared; the N line and the PE line are connected in reverse; the leakage of the equipment causes the phase line and the ground line to short-circuit; the ground is not equipotential, and if your ground wire is connected to the ground in different places, it will cause a potential difference. There are also interference problems such as high frequency of interference sources, etc. Finally, there is a large current flowing near the PE line, and some stray currents will be transmitted to the PE line through the ground.