What is grounding and why. How does grounding work in a home network. How to protect yourself from electric shock
In order to ensure reliable protection when working under voltage, electrical installations are grounded. Protective grounding is intentional electrical connection installation housing with a grounding device. According to the principle of operation, all grounding is divided into two types. It can be performed in the form of protective grounding and grounding, which have exactly the same function, which consists in protecting people from the effects of electric current, in case of touching the case or other parts with broken insulation.
The essence of protective grounding
With a protective clamping device, a deliberate connection of parts of electrical installations and a grounding device is carried out. Thus, electrical safety is ensured in case of accidental contact with certain parts that are energized. This situation, as a rule, occurs during an insulation breakdown, when voltage appears between the case and the phase. In the presence of grounding, the current will not pose a danger, since the conductor will act protective earth, which has a very low .
Main constituent parts grounding is directly grounding and grounding conductors. Grounding conductors can be natural and artificial. In the first case, this metal constructions having a reliable connection to the ground. Earthing electrodes of artificial origin are steel rods, pipes or angles, the length of which must be at least 2.5 m. They are hammered into the ground and interconnected using welded wire or steel strips. To make grounding more efficient, it is necessary to reduce its resistance by increasing the number of artificial grounding conductors.
Protective earthing device
The essence of the protective is the deliberate electrical connection of certain parts of electrical installations with a neutral wire.
As a rule, such electrical installations are not under normal voltage. In these cases, any phase shorted to the case leads to its short circuit with the neutral wire. There is a current with very great value therefore, the equipment must be quickly and completely switched off. This is precisely the main function of zeroing. Whole structure protective zeroing consists of a zero working and zero protective conductor.
Grounding a private house or apartments. Many people wonder if they should ground a private house or can they do without it? The answer is unequivocal - grounding a private house is necessary, moreover, according to the PUE during the construction of new and overhauls old houses, grounding of a private house is required. Installation of grounding of a private house is milestone when installing the power supply system of your private house, cottage or apartment. Properly designed grounding of a private house is the electrical safety of your home, electrical appliances, and most importantly, health and life.
To begin with, let's turn to the electrical literature, in particular to the Rules for the Construction of Electrical Installations, according to clause 1.7.28, grounding a private house:
"This is an intentional electrical connection of any point in the network, electrical installation or equipment with a grounding device."
I will not go into the abstruse formulations of textbooks or specials. literature, I will try to explain why it is necessary to ground a private house in a simple accessible language.
If a in simple words, grounding a private house is a wire connection between the equipment case and the ground loop.The grounding of a private house is a common mello-construction, assembled according to given dimensions, from certain materials and “hidden” in the ground.
Grounding a private house (metal structure) using copper wires, section not less than 10 sq. mm. or steel plate
connects to, in which the ground wire through the terminal block is connected to the ground wires of cables laid in the house or apartment to sockets, lamps and other electrical receivers.
Sockets, which must be three-pin (phase-zero-earth), through a special third "ground" contact, are connected with a plug to our household electrical appliances.
That is, the following "route" of the ground conductor PE is obtained: electrical appliance - plug - socket - terminal block in the electrical panel - ground wire (bus) - ground loop - earth.
Grounding a private house is done primarily for the electrical safety of people. Surely, many are familiar with such a situation when, touching an old refrigerator or washing machine, it slightly, but sometimes very noticeably, shocks. This happens in the old housing stock, where there is no grounding of a private house, i.e. only two wires are suitable for sockets: phase and zero, without a third protective RE wires. It shocks due to poor insulation of the refrigerator or washing machine (the insulation of the electrical wire, motor, compressor, etc. is damaged), and voltage (potential) appears on their case. And when you touch the body of the refrigerator or washing machine, for example, with your hand, especially if it is wet, you just “ground” the refrigerator or washing machine, and then a small current “runs” through you into the “ground”.
If there is a third protective wire PE in your electrical network at home, cottage or apartment, then if the insulation of the refrigerator or machine is broken, the current will “run away” through it to the ground loop. And when you touch the body of electrical equipment that is grounded, but with poor insulation, you will not feel anything, because the current always "runs" along the path of least resistance. In our case, human resistance ( about 1000 Ohm) will be much greater than the resistance of the protective wires + ground loop resistance, which will be approximately several dozens Ohm.
Grounding a private house necessary to protect our household electrical appliances. A person is often a "carrier" of a static charge, which depends on many factors, ranging from clothing to the level of humidity in the room, while the current is very small, but the voltage reaches several thousand volts that can damage delicate electronics in electrical appliances.
But grounding a private house will prevent this from happening and “take away” static electricity to the ground. Also, grounding a private house does not allow a static charge to accumulate to significant values already on the electrical appliances themselves, in this case, the charge constantly “flows” into the ground.
This is a simple and, I hope, understandable explanation of why it is necessary to ground a private house, cottage or apartment. An electric charge, whether it is damage to the insulation of an electrical appliance, or accumulated statically, when grounded, constantly “leaves” into the ground, because. the body of electrical equipment and the ground loop of a private house, figuratively speaking, are one.
How to properly mount the grounding of a private house yourself can be read in a separate article "".
Thank you for your attention.
From school course physics, every person remembers that an electric current cannot arise from nowhere, it is the movement of charged particles in a conductor, which can serve as a wire. But also, many people remember, from the course of life safety, that electric current is dangerous for human life. When does the danger of getting an electric shock arise? This happens if a person touches bare wires, or a device that is plugged into an ungrounded outlet. In their right mind, no adult will touch bare wires, but everyone can plug the kettle into a socket without grounding.In order for a “hit” to occur, you need to create electrical circuit. In the case when an ungrounded socket is used, the current enters the device, accumulates in it and passes to the person as soon as he touches it. The person in this case is a conductor, as he stands on the floor. The current passes through the body and then goes to the floor. AT best case, the victim will feel discomfort, and at worst - go in an ambulance to the hospital.
How to protect yourself from electric shock?
When there are a lot of electrical appliances in the house, people do not always use only grounded outlets. In a hurry, they forget about the importance of grounding or do not know at all whether they have it in their apartment, and simply stick the plug into the outlet that turned out to be closer. Constantly using a non-grounded socket to operate a metal electrical appliance, there is a high risk that static voltage will accumulate in it and a person will receive an electric shock. To avoid this, you need to install sockets with grounding contacts in every room at home. Of course, the risk will not disappear completely, because it is impossible to be completely sure of the quality of the outlets, but it will still become less.Those people who have a big house kitchen stove and a washing machine, must additionally ground the appliances. To do this is quite simple, you need to take a special wire, attach it to the body of the device and send it to the ground. In private homes, this can be easily done, but in an apartment there may be problems with where to send this ground wire.
Due to the fact that death from electric shock has long ceased to be a rarity, most developers, before putting the house into operation, equip the power grid special devices protective shutdown. His job is that, in the event of a current leakage, he disconnects the entire apartment from electricity, thereby saving residents from fatal injury. To date, this is the most effective protection from electric shock. Anyone can install such a system, for this it is enough to contact the appropriate company.
A grounded outlet in your home not only protects against possible damage electric shock. The presence of grounding makes the operation of complex home appliances: washing machine, computer, video and audio equipment.
Outwardly, with grounding, it differs from the usual one by the presence of built-in grounding brackets made of metal. In world practice, many options for the design of sockets with grounding are used, but in Russia this option was chosen, with brackets. The choice is due to the design, in which, when the plug is connected, the terminals (brackets) intended for grounding first come into contact, only then the phase ones. This type of device is called Shuko, or type F (CEE 7/4).
Why is grounding necessary?
This term in electrical engineering means the connection of current-carrying elements of electrical installations, electrical appliances with the ground. The main task of grounding is protection against electric shock. In its presence, the electrical potential goes into the ground, protecting a person. Simple devices are used to ensure the process. Most often, this is a metal rod dug to a depth of at least 2 meters. Sometimes several rods are buried, interconnected - the quality of grounding is higher, the more total area soil contact.
There is another concept - a connection with "". This refers to the contact of the body of electrical equipment (for example, a switchboard, a stationary type of power tool) with the "zero" wiring. Such an operation is necessary to protect against short circuits in electrical equipment. Ideally, "zero", "ground" are connected.
Features of mounting a socket with grounding
Such a socket is installed by analogy with a traditional connection device, but taking into account the presence of three, not two, contacts. One of important points during installation - the color of the wires. The wire originally intended for the ground connection is always green-yellow. The wire under the zero contact is blue-blue. The phase wire may have different colour, but in any case it will be different from zero and ground. It is still recommended to check the correct connection with a tester.
When arranging grounding in private (suburban) housing, there are usually no difficulties, but problems can arise in a multi-storey building. There are 2 ground connection options. In the first case, you can lead the wire to the shield body on landing(it must be grounded). The second option is to connect the ground wire and the "zero". This option makes it possible to connect RCDs, differential automata.
Everyone knows that electricity is an essential attribute modern man. Without the use of electricity, it is impossible to turn on the kettle to drink tea or coffee, heat up food in the microwave or watch TV. Despite the indispensability of electricity, we should not forget about its deceit. A lot of unpleasant cases happen with electric shock, there are even lethal situations.
Greetings Dear friends and readers of the Electrician in the House website. Many felt an unpleasant electric shock when they accidentally touched bare wire. But in everyday life there are situations when a person can be shocked, even if he touches a seemingly harmless household appliance. Why is this happening?
As a rule, this happens when the internal insulation is damaged and the device does not have an earth connection. In this article we will try plain language explain to the reader what grounding is, how grounding works and why it is needed.
What does grounding protect against?
The main purpose of grounding in electrical network is protection. For the operation of electrical appliances in the wiring, two wires are provided: phase and zero.
The protection that grounding provides consists in connecting a third conductor connected directly to the ground electrode, which in turn is connected to the ground loop. Thanks to grounding, you can not worry that a malfunction that has arisen due to the fault household appliance an emergency situation will result in an electric shock to someone around you.
Friends, let's see what emergencies can occur and what is it?
The danger of breaking an electrical device is that its case may be energized, thereby making it dangerous. This circumstance may arise if the internal insulation is damaged. For example, when the wires of the device shrink or melt over time, and come into contact with the metal case of the household appliance.
It is impossible to visually notice such an emergency breakdown, but it is enough to touch the electric stove or washing machine, the electric shock will pass immediately.
After many such situations, the question arises: and whether it can effectively protect. The strength of such a blow may be different depending on the condition of the person and the surrounding conditions.
What happens if case not connected to ground? By itself, such a breakdown does not represent anything. Washing machine with a pierced body, it has worked and will continue to work. It will perform its functions perfectly until you touch it.
The thing is that a person is more than 70% water and is an excellent conductor of electricity. When you stand on the floor or touch a wall, your body can act as a conductor. When touching a damaged case, current will begin to flow through your body and into the ground.
Of course, you can avoid electric shock if you wear rubber gloves or shoes, but no one walks like that in the house. If you do not have grounding in your house, and the device beats with current, you should remember that even low voltage can lead to deplorable circumstances.
A value of 50 mA is already dangerous for humans. Such small value current can lead to cardiac fibrillation and even death.
In order not to worry about your life and the health of your family, it is important that the ground is connected in the house. In this case, the dangerous potential available on the instrument case will go into the ground, protecting you from impact. This is . In addition, it is recommended to install an RCD in addition to grounding, which will turn off damaged equipment at the slightest leak.
The principle of operation of grounding
After the devices are grounded, a breakdown of the internal insulation is not terrible for us. If for some reason the body of the device is energized, a short circuit will occur between the phase and ground. As a result, it will work circuit breaker. Due to properly installed grounding and the operation of the machine, a person will not be shocked.
However, there are some nuances of electrical engineering. Not always, during a voltage breakdown on the case, the machine can knock out, and in such cases, a residual current device will become a great helper.
How electrical grounding works
As for the residents of the private sector, in general, in these areas, electricity is supplied to the plots by overhead power lines. As a rule, these are two-wire lines, which consist of a phase and a neutral wire. In our country, power lines leave much to be desired, because there can be many twists on one cable running along the main line.
Gusts of wind, falling branches and precipitation can break off at any time power cable and if you do not have a protection system in the form of grounding and an RCD installed in your house, then not only the owner of the house, but also all his equipment can suffer. Here, the installation of grounding is a particularly relevant issue.
Today you can create your own good protection for the house and create a ground with my own hands, ensuring the safety of appliances and the health of households.
Properly made and installed system protection will be able to save electrical appliances even at the moment of a break in the line leading to the house. Currently individual work grounding the house in conjunction with the RCD is considered a popular means of protection against electric shock in your own home.
Grounding work in the private sector
In this section, we will analyze how grounding works using the example of a private house. The power supply scheme of the house shown in the figure consists of an overhead line. The overhead line is two-wire, the most common in the private sector. It consists of two phase wires (marked in red in the figure) and zero ( of blue color). The neutral wire is zero working and protective at the same time. That is, a combined conductor. In electrical literature, it is referred to as a PEN conductor.
In order to divide this conductor into two independent working and protective ones, a special branch is made in the inlet shield of the house to the ground loop. After that, two neutral conductors come out of the input shield, which have different purpose. One of them is a working zero, which serves to operate the devices. Another protective zero - grounding conductor, must have a yellow-green marking and a PE designation.
In the "Electrical Installation Rules" such a grounding system is referred to as TN-C-S. The internal wiring of the house must be three-wire, that is, phase, zero and ground. All sockets in the house must be properly grounded. In this case, the body of the potentially dangerous device will be connected to the protective conductor through the grounding contact of the socket. Particularly at risk is the so-called wet technique these are water heaters, pumps, dishwashers and washing machines.
If during operation the phase wire, as a result of insulation breakdown, comes into contact with the body of the device (for example, this is the case of a refrigerator), then a short circuit will occur between the phase wire (red) and the ground wire (yellow-green), as a result of which the power machine will turn off.
Imaginary protection or incorrect grounding
There are situations where grounding can be dangerous. This is subject to INCORRECT CONNECTION. Friends now consider the case of incorrect ground connection and compare it with the case discussed above.
The figure shows a diagram of incorrect grounding. Its essence is to connect the ground conductor (ground wire in the electrical wiring) to the zero working one. The neutral wire is grounded at the substation, why not ground it from it? Unfortunately, there are specialists in our industry who make such mistakes.
What is the danger? AT good condition the equipment will work flawlessly, everything electrical devices will do their job. Friends, let's now consider another situation when neutral wire on the line was interrupted as a result strong wind, while the red is still intact.
When closing phase wire in this case, a short circuit will not occur on the case, since ground wire, which is also a zero worker, is cut off on the way to the house, there is no potential difference between the phase and ground wires, and a short circuit will not occur. From here it is not difficult to guess that the circuit breaker will not turn off, since it simply has nothing to react to (there is no short circuit current).
It follows from this that the body of the refrigerator, being under dangerous voltage, will wait for its victim. The strength of the electric shock in this situation will directly depend on how close the person is to the ground. The better the contact, the harder it hits.
In some cases, an electric shock through the body of the device can be fatal, so that trouble does not happen, you need to know how grounding works in the house.
For example, you touch a pierced electric water heater and at the same time take hold of water pipe. It is also dangerous to take hold of the body of the device, which is energized while standing barefoot on concrete floors. Such a floor can serve as a conductor.
How does an ouzo work with grounding
The sensitivity of the grounding system, and, accordingly, electrical safety can be increased by installing a residual current device (RCD) in the electrical panel. This device reacts to current leakage and turns off when it occurs, thereby de-energizing equipment with damaged insulation. RCD works even in those cases if there is the slightest leakage of current.
In reality, current leakage can occur both through the grounded case of the device, and through the human body (if there is no grounding in the house), which is less pleasant. The figure shows the situation when the current passes through the human body.
For example, a person touches the body faulty device, the case of which is not grounded. At the moment of touch, a current begins to flow through a person, and the RCD, reacting to it, will instantly turn off. The duration of the electric shock for a person in this case will be equal to the time the RCD is turned off. It is usually equal to tenths of a second.
Insignificant and short-term exposure to current in most cases does little harm, a person gets pain and discomfort and fear, which disappears after a few minutes.
Seemingly perfect option protection, but not everything is so smooth. Even such a protection system has its drawbacks:
- if the device does not have grounding, then, therefore, the RCD will not be able to fix the leak, and it will be possible to understand the breakdown only after a small, but electric shock;
- in fact, RCD is a complex electronic device, which cannot operate immediately, it takes time to trip, therefore, protection with RCD alone may be too slow.
- due to the high cost of RCDs, homeowners tend to save money and buy low-quality devices or install one RCD for the whole house, in which case it is difficult to guarantee timely operation.
Do not use RCD devices of dubious quality and little-known brands. Each person is responsible for their own protection, so you need to buy only original and certified goods. AT this moment the market is full of electrical equipment from various manufacturers and you need to be responsible for such a purchase.
Friends, we have examined the principle of grounding, and what can happen when wrong way of grounding. The main advantage of such a connection scheme is that it has its own individual ground loop, and in the event of a wire break on the power line, it will not be able to affect performance in any way.
Important! Do not think that if the house has grounding, then you do not need to use an RCD. Even with the slightest leak, the device can fix the problem and turn off the damaged section of the network, ensuring human safety and health.
Electricity is a friend and enemy of a person, therefore, in order to prevent something unforeseen from happening, it is necessary to do the wiring correctly, and to know How does grounding work in a house?. If there is no knowledge and experience in working with electricity, then it is better to entrust such work to professionals who will do everything, not only quickly, but also qualitatively, taking into account all norms and requirements.
In the first part (theory), I will describe the terminology, the main types of grounding (appointment) and the requirements for grounding.
In the second part (practice) there will be a story about traditional solutions used in the construction of grounding devices, listing the advantages and disadvantages of these solutions.
The third part (practice) in a sense will continue the second. It will contain a description of new technologies used in the construction of grounding devices. As in the second part, with a list of the advantages and disadvantages of these technologies.
If the reader has theoretical knowledge and is only interested in practical implementation - he had better skip the first part and start reading from the second part.
If the reader has necessary knowledge and wants to get acquainted only with new products - it is better to skip the first two parts and immediately proceed to reading the third.
My view of the described methods and solutions is somewhat one-sided. I ask the reader to understand that I do not put forward my material as a comprehensive objective work and express my point of view, my experience in it.
Some of the text is a compromise between accuracy and the desire to explain in “human language”, therefore simplifications are allowed that can “cut the ear” of a technically savvy reader.
1 part. grounding
In this part I will talk about terminology, about the main types of grounding and about quality characteristics grounding devices.It is possible to increase the area of contact of the earth electrode with the ground either by increasing the number of electrodes, connecting them together (adding the areas of several electrodes), or by increasing the size of the electrodes. When using vertical ground electrodes, the latter method is very effective if the deep layers of the soil have a lower electrical resistance than the upper ones.
B1.2. Soil electrical resistance (specific)
Let me remind you: this is a value that determines how well the soil conducts current through itself. The less resistance the soil will have, the more efficiently / easier it will “absorb” the current from the ground electrode.Examples of soils that conduct electricity well are saline soils or highly moistened clay. Ideal natural environment for passing current - sea water.
An example of a “bad” soil for grounding is dry sand.
(If interested, you can see the table of soil resistivity values used in calculations of grounding devices).
Returning to the first factor and the method of reducing the ground resistance in the form of increasing the depth of the electrode, we can say that in practice, in more than 70% of cases, the soil at a depth of more than 5 meters has several times lower electrical resistivity than at the surface, due to more humidity and density. Often found ground water which provide the ground with very low resistance. Grounding in such cases is very high quality and reliable.
IN 2. Existing regulations ground resistance
Since the ideal (zero spreading resistance) cannot be achieved, all electrical equipment and electronic devices are created based on some normalized ground resistance values, for example, 0.5, 2, 4, 8, 10, 30 or more Ohm.For guidance, I will give the following values:
- for a substation with a voltage of 110 kV, the resistance to current spreading should be no more than 0.5 Ohm (PUE 1.7.90)
- when connecting telecommunications equipment, grounding should usually have a resistance of no more than 2 or 4 ohms
- for reliable operation of gas dischargers in protection devices overhead lines connections(For example, the local network on the basis of a copper cable or a radio frequency cable), the ground resistance to which they (arresters) are connected must be no more than 2 ohms. There are instances with a requirement of 4 ohms.
- at a current source (for example, a transformer substation), the ground resistance should be no more than 4 ohms at a linear voltage of 380 V of a three-phase current source or 220 V of a source single-phase current(PUE 1.7.101)
- at the ground used for connection lightning rods, resistance should be no more than 10 Ohm (RD 34.21.122-87, p. 8)
- for private houses, with connection to the mains 220 Volt / 380 Volt:
- using TN-C-S systems it is necessary to have a local ground with a recommended resistance of not more than 30 ohms (I focus on PUE 1.7.103)
- when using the TT system (isolation of ground from the neutral of the current source) and the use of a residual current device (RCD) with a trip current of 100 mA, it is necessary to have a local ground with a resistance of not more than 500 Ohm (PUE 1.7.59)
IN 3. Ground resistance calculation
For the successful design of a grounding device with the required grounding resistance, as a rule, typical configurations of the grounding conductor and basic formulas for calculations are used.The configuration of the earth electrode is usually chosen by the engineer based on his experience and the possibility of its (configuration) application on a particular object.
The choice of calculation formulas depends on the selected configuration of the ground electrode system.
The formulas themselves contain the parameters of this configuration (for example, the number of ground electrodes, their length, thickness) and the soil parameters of a particular object where the ground electrode will be placed. For example, for a single vertical electrode, this formula would be: 
The calculation accuracy is usually low and again depends on the soil - in practice, discrepancies in practical results occur in almost 100% of cases. This is due to its (soil) great heterogeneity: it changes not only in depth, but also in area - forming a three-dimensional structure. The existing formulas for calculating grounding parameters can hardly cope with one-dimensional soil heterogeneity, and the calculation in a three-dimensional structure is associated with huge computing power and requires extremely highly trained operator.
In addition, to create an accurate soil map, it is necessary to carry out a large amount of geological work (for example, for an area of 10 * 10 meters it is necessary to make and analyze about 100 pits up to 10 meters long), which causes a significant increase in the cost of the project and most often is not possible.
In the light of the foregoing, the calculation is almost always a mandatory, but indicative measure and is usually carried out according to the principle of achieving ground resistance “no more than”. Averaged values are substituted into the formulas resistivity soil, or their largest values. This provides a “margin of safety” and in practice is expressed in obviously lower (lower means better) ground resistance values than expected during design.
Construction of grounding conductors
In the construction of grounding electrodes, vertical grounding electrodes are most often used. This is due to the fact that it is difficult to bury horizontal electrodes to a great depth, and with a small depth of such electrodes, their grounding resistance increases very much (deterioration of the main characteristic) in winter period due to freezing of the upper layer of the soil, leading to a large increase in its electrical resistivity.)
Grounding devices and systems for equalizing electrical potentials in electrical installations containing information processing equipment (google)
Tags: Add tags