What is the tt system. Why is it dangerous to independently perform grounding in an apartment (converting TN-C to TN-C-S). TN-C earthing system

The most perfect, for today, grounding system "TN-S"(type of electrical network) strongly recommended for use by the PUE (Electrical Installation Rules). In Russia, a system similar to TN-C is still used (TN-C system is prohibited in new construction, in single-phase and direct current. This requirement does not apply to branches from overhead lines with voltage up to 1 kV to single-phase consumers of electricity - PUE 1.7.132).

Grounding system "TN-S"- from supply substations two different neutral wires go to the consumer: N - working zero and PE - protective zero, thereby ensuring the greatest electrical safety, both for humans and for electrical consumers.

In the event of a breakdown to the case, the leakage current flows through the grounding (grounding) conductor to the protective zero - PE, which causes a trip RCD(currents through the differential transformer to the load and back are not equal). And with a large leakage current, it works circuit breaker

In general, the "TN-S" grounding system was first developed in the 1930s and implemented in the territory European countries, in which the last 50 years is the main scheme for the protection of electricity consumers. Most likely, the same task is facing Russian enterprises electrical networks, since when designing new lines for the development of power supply, it is recommended to use a five-core electrical installation for three-phase inputs and three-wire - for single-phase connection, starting from the power source and ending with the outlet of a specific subscriber. As you know, recommendations very often turn into norms and provisions of standards, but for now one of the stages of such a transition is mandatory electrical installation according to the system grounding TN-С-S, since the direct transition from TN-С to TN-S involves large capital investments and is comparable to the construction of a new hydroelectric power station.

Fig1. TN-C system

Fig2. TN-S system

Fig3. TN-C-S system

What is so remarkable about it, if it is required, albeit a gradual, but mandatory transition? To find out, let's first look at it. wiring diagram. It is completely identical with traditional system power supply, where, in addition to current-carrying lines, neutral wire nickname, with the important difference that another neutral conductor is added to the circuit, which does not require re-grounding neither on the "N" line, nor on the "PE" line, which is carried out only on the initial power source. Thus, allowing them to separate their working and protective functions on separate power rails. That is, the working conductor "N" performs only the functions of EMF (electromotive force - a physical quantity that characterizes the work of external (non-potential) forces in sources of constant or alternating current. In a closed conducting circuit, the EMF is equal to the work of these forces in moving a single positive charge along the circuit), and the “PE” conductor is only a protection function, while achieving complete isolation from each other. Such a wiring diagram is especially relevant in terms of problems when there is absolutely no control over the state of protective grounded circuits, as you can see, the need for this is completely eliminated.

Now, after we figured out the electrical circuit, it becomes obvious that such a "TN-S" grounding system provides maximum protection electrical equipment and the person himself. Moreover, it eliminates high-frequency pickups and other interference on consumer lines coming from some devices. similar situation, each of us probably observed when someone used an electric razor in the next entrance, sometimes a drill or welding machine, rattling distortion appeared on the TV screen. Such a system, if not completely, then certainly excludes most of the interference, oscillatory and electromagnetic excitations that sometimes occur in electrical networks. Therefore, the TN-S grounding system is very fond of employees who work with information, telecommunications, radar or location equipment, since maximum isolation from casings and cases of other electrical devices, as well as pickups through the "ground", in other words, from interference sources.

Conventions grounding systems:

First letter is the state of the source neutral with respect to earth.

T- grounded neutral.
I- isolated neutral.

Second letter- state of exposed conductive parts relative to earth.

T- exposed conductive parts are earthed regardless of the relation to earth of the neutral of the power supply or any point of the supply network.
N- exposed conductive parts are connected to a dead-earthed neutral of the power source.

Letters after N- combination in one conductor or separation of the functions of the zero working and zero protective conductors.

S- zero working (N) and zero protective (PE) conductors are separated.
With- the functions of the zero protective and zero working conductors are combined in one conductor (PEN-conductor).

The generally accepted method of ensuring safety when working with electrical equipment is grounding. In the PUE, in the list of measures to protect people from exposure to electric current, protective earth ranks first (clause 1.7.51). This measure involves the connection of open conductive parts of the electrical installation with a grounding device. Depending on the design features electrical installations and networks, the ground loop can be organized in several ways. The system in accordance with which grounding is carried out is determined at the design stage or prescribed by the technical specifications issued by the electric grid organization. The subject of this article is the TT grounding system, the principle of operation and scope of which will be detailed below.

General description and principle of operation

The use of the TT system applies to electrical networks, the neutral of which is deafly grounded. The essence of this method lies in the fact that the conductive parts of electrical equipment are connected to a grounding device located on the consumer side. There is no electrical connection between this device and the grounding conductor to which the neutral of the transformer at the substation is connected.

The figure schematically shows the TT system, through which the building is grounded:

Application area

Consider the cases in which this type of grounding is used. It should be noted that the TT system is in some way an extraordinary measure. The fact is that the PUE prescribes, as a rule, TN grounding in networks with a solidly grounded neutral. It has several varieties, the common design feature of which is the combination of the earthing circuits of the neutral of the transformer and the electrical installations of the consumer. Protection performed according to this principle is most easily implemented from the point of view of the consumer connecting to the electrical network. This system does not require the construction of a grounding device at the customer's site.

The use of CT earthing is only prescribed when the TN system does not provide required level security. This usually occurs when the technical condition of the supply air line is unsatisfactory, especially if it was built according to a temporary scheme. Under such conditions, as a rule, there is a high probability of damage to the grounding conductor, that is, the loss of electrical connection between the grounding device at the substation with the consumer's grounding circuits. This situation is fraught with the fact that in the event of an insulation breakdown, the contact voltage to the electrical equipment housings may turn out to be equal to the operating voltage of the network. For this reason, the main scope of the TT scheme is objects whose power supply is temporary. For example, construction sites, wagons, etc.

Quite often there are cases when TT grounding is used in a private house or in a country house. The implementation of such a scheme is quite laborious, especially for a private owner. Questions of how to make a ground electrode and install an RCD can, perhaps, only be solved by specialists. Not every owner can build a grounding device on his site that meets the requirements of the rules. It can also be added to the above that the use of the system should be coordinated with the organization providing electricity.

In accordance with the PUE, the operation of electrical equipment, which is grounded according to the TT system, is prohibited without the use of RCDs. Figure 2 illustrates the RCD connection diagram.

(RCD), this is a protection system that turns off the installation when it occurs due to damage to the insulation. This device responds to the difference in currents flowing through the phase and neutral wires, therefore it is called a differential current circuit breaker. If the insulation of the electrical installation is damaged, a shunt circuit is formed through the equipment case to the ground. As a result, a leakage current to ground is generated.

Requirements for a grounding device

most important characteristic grounding device is its resistance. The requirement for this parameter, if grounding is performed according to the TT system, can be expressed as follows:

R ≤ 50V/Iav.uzo

In this case, in the case of using several protective shutdown devices, the differential tripping current of the device where it has the maximum value is taken into account.

In addition to this requirement, the main one must be met. The essence of the event is to interconnect the following structures:

• Grounding device made on site.
• Metal pipelines for heating, water supply (cold and hot), sewerage, gas supply.
• Metal structures related to the frame of the building.
• metal parts ventilation systems as well as air conditioning systems.
• Grounding device, which is part of the lightning protection of a private house.

Advantages and disadvantages

Let's list the pros and cons that CT grounding brings with it. An absolute plus should include a certain independence from possible damage to the power line in terms of safety. The presence of a local grounding device located in close proximity to grounding objects makes it extremely unlikely to break communication with it.

On the other hand, the construction of a full-fledged grounding device, which has the necessary characteristics, is quite troublesome, requiring earthworks. Here you also need to add the need to use an RCD, which complicates the circuit and requires additional financial costs.

Electricity in our houses and apartments comes from electrical wires overhead or cable lines from transformer substations. The configuration of these networks has a significant impact on performance characteristics systems and, especially, the safety of people and household appliances.

In electrical installations, there is always a technical possibility of damage to equipment, the occurrence of emergency modes, and electrical injury to a person. Proper organization grounding systems allows you to reduce the possibility of risks, maintain health, and eliminate damage to home appliances.

Reasons for using a TT earthing system

According to its purpose, this circuit is designed for such a case when a high degree security cannot be provided by other common systems. This is very clearly stated in paragraph PUE 1.7.57.

Most often this is associated with low level the technical condition of power lines, especially those using bare wires located in the open air and fixed on supports. They are usually mounted in a four-wire circuit:

three phases of voltage supply, offset by an angle of 120 degrees from each other;

one common zero that performs the combined functions of a PEN conductor (working and protective zero).

They come to consumers from a step-down transformer substation, as shown in the photo below.

AT countryside such highways can be of great length. It is no secret that wires sometimes clash or break due to poor quality twists, falling branches or whole trees, surges, gusts of wind, ice formation in frost after a wet snowfall, and for many other reasons.

This happens quite often, since it is mounted with the bottom wire. And this causes a lot of trouble to all connected consumers due to the occurrence of voltage distortions. In such a circuit, there is no protective PE conductor connected to the ground loop of the transformer substation.

Cable lines are much less likely to break zero because they are located in closed ground and are better protected from damage. Therefore, they immediately implement the most secure TN-S grounding system and gradually perform the reconstruction of TN-C to TN-C-S. Consumers, connected by overhead wires, are still practically deprived of such an opportunity.

Now many owners land plots start building country houses, entrepreneurs organize trade in separate pavilions and kiosks, manufacturing enterprises create prefabricated household premises and workshops, or generally use separate trailers that are temporarily powered by electricity.

Most often, such structures are made of metal sheets that conduct electricity well or have damp walls with high humidity. Human safety in such conditions can only be ensured by a grounding system made according to the TT scheme. It is specially designed to work in conditions where the potential of the network has a high probability of an emergency appearance on current-carrying walls or equipment cases.

Principles of constructing a grounding scheme according to the TT system

The main safety requirement in this situation is ensured by the fact that the protective PE conductor is created and grounded not at the transformer substation, but at the consumption facility itself. electrical energy without connection with the working N-conductor connected to the grounding of the supply transformer. These zeros should not contact and combine even if a separate ground loop is mounted nearby.

In this way, all dangerous conductive surfaces of buildings made of metal and the case of connected electrical appliances are completely separated by a protective PE conductor from operating system power supply.

Inside the building or structure, a protective PE conductor is mounted from a rod or strip of metal, which serves as a busbar for connecting all dangerous elements with conductive properties. On the opposite side, this protective zero is connected to a separate ground loop. The PE conductor assembled in this way combines all areas with a risk of dangerous voltage into a single potential equalization system.

Hazardous connection metal structures to protective zero can be carried out with a multi-core flexible wire of increased cross-section, marked with yellow-green stripes.

At the same time, we once again draw attention to the fact that it is strictly forbidden to combine elements of building structures and metal cases of electrical devices with a working zero N.

Technical requirements for ensuring safety in the TT system

Due to an accidental break in the insulation of electrical wiring, a voltage potential can suddenly appear anywhere in an unconnected, but conductive part of the building. A person who touches it and the earth immediately finds himself under the influence of an electric current.

Circuit breakers protecting against overcurrents and overloads can only be indirectly used to relieve voltage in this case, since part of the current will bypass the operating zero circuit, and the resistance of the main ground loop must be very low.

To protect a person with the operation of circuit breakers, it is necessary to create a condition for the formation of a leakage potential on an open current-carrying part of not more than 50 volts relative to the ground potential. In practice, this is difficult to achieve for a number of reasons:

high multiplicity of short-circuit currents of the time-current characteristic used by the designs of various switches;

high resistance of the ground loop;

the complexity of technical algorithms for the operation of such devices.

Therefore, preference in creating a protective shutdown is given to devices that respond directly to the appearance of a leakage current branching off from the main calculated load flow path through the PE conductor and localizing it by removing voltage from the controlled circuit, which is performed only by RCDs or difavtomatov.

It is possible to eliminate the risks of electrical injury with this method of grounding only if the four main tasks are integrated:

1.correct installation and operation protective devices type of RCD or differential automata;

2. maintaining the working zero N in a technically sound condition;

3. use of protective devices against surges in the network;

4. correct operation of the local ground loop.

RCD or difavtomaty

Almost all parts of the building's electrical wiring must be covered by the zone of protection of these devices from the occurrence of leakage currents. Moreover, their operation setting should not exceed 30 milliamps. This will ensure that the voltage is turned off from the emergency section in the event of a breakdown in the insulation of the electrical wiring, exclude accidental contact of a person with a spontaneously arisen dangerous potential, and protect against electrical injury.

Installing a fire RCD with a setting of 100 ÷ 300 mA on the input shield to the house increases the level of safety and ensures the introduction of a second degree of selectivity.

Working zero N

In order to correctly determine leakage currents, it is necessary to create technical conditions for this and eliminate errors. And they arise immediately when the circuits of the working and protective zeros are combined. Therefore, the working zero must be reliably separated from the protective one, and they cannot be connected. (Third reminder!).

Network surge protection

The occurrence of electrical discharges in the atmosphere, associated with the formation of lightning, are random, spontaneous. They can manifest themselves not only as an electric shock to the building, but also as a hit on the wires of an overhead power line, which happens quite often.

Power engineers apply protective measures against such natural phenomena, but they are not always effective enough. Most of the energy of a lightning strike is taken away from power lines, but some of it has a harmful effect on all connected consumers.

It is possible to protect yourself from the action of such bursts of overvoltage coming through the supply overhead line using special devices - or impulse surge protection devices (SPD).

Maintaining the local ground loop in good condition

This task rests primarily with the owner of the building. No one else will deal with this issue on their own.

The ground loop is buried for the most part in the ground and in this way is hidden from accidental mechanical damage. However, solutions are constantly found in the soil. various acids, alkalis, salts that cause redox chemical reactions with metal parts of the contour forming a layer of corrosion.

Due to this, the conductivity of the metal at the points of contact with the ground deteriorates and the overall electrical resistance of the circuit increases. Judging by its size technical capabilities grounding and its ability to conduct fault currents to the ground potential. This is done by electrical measurements.

A good ground loop must reliably pass the current setting of the residual current device, for example, 10 milliamps, to the ground potential and not distort it. Only in this case, the RCD will work correctly, and the TT system will fulfill its purpose.

If the resistance of the ground loop is higher than normal, then it will prevent the passage of current, reduce it, which can completely eliminate the protective function.

Since the operating current of the RCD depends on the complex resistance of the circuit and the state of the ground loop, there are recommended resistance values ​​that allow for guaranteed operation of the protections. These values ​​are shown in the picture.

The measurement of these parameters requires professional knowledge and accurate specialized instruments that work, but use a sophisticated algorithm with additional scheme connections and a strict sequence of calculations. A high-quality ground loop resistance meter stores the results of its work in memory and displays it on an information board.

According to them, with the help of computer technology, graphs of the distribution of the electrical characteristics of the circuit are plotted and its state is analyzed.

Therefore, accredited electrical laboratories with special equipment are engaged in similar work.

The measurement of the insulation resistance of the ground loop must be done immediately after the electrical installation is put into operation and periodically during operation. When the obtained value goes beyond the norm, exceeding it, then additional sections of the circuit are created, connected in parallel. The completion of the correctness of the work performed is checked by repeated measurements.

Dangerous circuit failures in a CT system

When considering the technical requirements for ensuring safety, four main conditions have been identified, the solution of which must be carried out in a comprehensive manner. Violation of any point can lead to sad consequences during the breakdown of the insulation resistance of the phase conductor.

For example, if a phase hits the body of an electrical appliance with a faulty RCD or a broken ground loop, it will lead to electrical injury. The circuit breakers installed in the circuit may simply not work, since the current through them will be less than the setting.

In this case, the situation can be partially corrected by:

introduction of a potential equalization system;

connecting the second selective RCD protection stage to the entire building, which was already mentioned in the recommendations.

Since the entire organization of work on the creation of grounding of the TT system is complex and requires precise execution of technical conditions, such installation should be entrusted only to trained workers.

To deal with grounding systems, I will define the basic concepts that will be used in this article. Of course, you can read paragraphs 1.7.3-1.7.7 of Chapter 7, PUE, if you like primary sources. Here I will not rewrite the PUE, I will simply tell you what you need to understand by individual words in this article.

First of all, what is the grounding of the eclectic network, in fact

Grounding of an electrical network is the connection of all conductive parts of electrical appliances open to touch (for example, cases) and accessible fittings (for example, metal water pipes) to the ground (literally).

Why is grounding necessary?

The earth, or rather the conductive part of the earth, has zero electrical potential at any point. Parts of electrical appliances through which no electric current flows in normal mode are completely safe for humans. Another situation is in an emergency in which current begins to flow through the housing of the household appliance. In such an emergency, touching the body would pose a serious danger to humans. It is to protect a person from electric shock, as well as to protect against the consequences of electrical accidents (for example, fire) that GROUNDING is intended.

Why does grounding protect a person?

As I said, the conductive part of the Earth has zero electrical potential. If an electric potential arises on the side of the conductor connected to earth (there is emergency situation), then it will tend to equalize with the zero potential of the earth and the current will flow in the direction of the earth. A special electrical device responsible for emergency turn-off power supply is also connected to ground. An electrical circuit occurs between the emergency conductor and the protection device, which disconnects the emergency section from the power supply.

But this protection scheme will work if all elements of the electrical network are connected to the ground. And speaking of all the elements of the network, we mean the elements of the network from generators supplying power to a simple outlet in the apartment.

Wherein. The scheme according to which the grounding of the main generator (source) of the power supply network is made must match all the grounding schemes of this network. Rather the opposite. Network grounding schemes must match the power supply grounding scheme.

There are three main electrical grounding systems TN; TT; IT.

TN earthing system (exposed parts connected to neutral)

At TN earthing system one point of the power supply of the electrical network is connected to the ground using a grounding electrode and grounding conductors. The ground electrode is in direct contact with the ground. With a TN earthing system, exposed conductive parts are connected to the neutral, and the neutral is connected to earth.

TN-C system

If the neutral is connected to protective conductors (earth) throughout the mains, such a system is called and denoted TN-C.

TN-S system

If the neutral and protective conductors are separated throughout the electrical network, and are combined only at the power source, such a system is called TN-S.

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A grounding system that allows the use of both the TN-C (4/2-wire) grounding system and the TN-S (5/3-wire) grounding system.

Important! With a TN-C-S earthing system, it is forbidden to use the TN-C system below the TN-S system, since any break in the neutral in the TN-C system will lead to a break in the protective conductor after the TN-S system. (See figure)

Earthing system TT-grounded neutral

At TT earthing system the middle point of the power supply is connected to ground. All conductive parts of the electrical network are connected to earth through an earth electrode different from the electrode of the power source. In this case, the spreading zones of both electrodes can intersect.

IT earthing system - isolated neutral

With an earthing system, IT is completely isolated from the entire electrical network, or the resistance of the earth connection tends to infinity.

The earth connection is one of the most important ways to protect a person from stray current in the electrical network. Appropriate grounding systems are used for this. Not only human safety, but also the proper functioning of electrical appliances and other protective equipment will depend on them.

Grounding systems are usually classified. The standards by which the type of protective grounding structure is determined have been adopted by the International Electrotechnical Commission and the State Standard of the Russian Federation. So it is customary to distinguish between several types of systems.

TN system. This type has characteristic difference from others - the presence of a dead-earthed neutral in the circuit. In TN, all open conductive sections of any electrical equipment are connected to a certain dead-earthed neutral section of a separate power supply by connecting protective conductors ("zero"). In this system, a solidly grounded neutral means that the “zero” of the transformer is connected to the ground loop. Used for grounding electrical equipment (TVs, computer system unit, refrigerator, boiler and other equipment).

Subsystem TN-C. This is a TN system where the protective and neutral conductors on the entire line are combined in one PEN. This means that a special protective grounding has been performed. This system was relevant in the 90s, but today it is outdated. Usually used for outdoor lighting to save money. Not recommended for installation in modern residential buildings.

Subsystem TN-S. In TN-S, the protective and neutral conductors are separated. This subsystem is considered the most reliable and secure, but this usually entails large financial costs. It is used to protect television communications, which will eliminate most of the interference in a low-voltage network. Subsystem TN-C-S. The TN C S earthing system is an intermediate circuit. In this case, the protective and working contacts must be combined in only one place. Often this is done in the main switchboard of the complex.

Compatible. And in all other parts of the TN C S system, these conductors must be separated from each other. This system is considered the most optimal solution for the electrical network of any building (industrial, residential, public).

Favorable ratio of quality and price. Other ways of connecting grounding electrical installations do not allow reliable operation on individual parts. Depending on the required level of resistance, the cross-sections of the conductors are selected.

TT system. A system of this type has a characteristic feature - the neutral conductor of the source is grounded, and the open conductive parts of electrical installations are connected to ground. The ground loop is independent of the grounded neutral of the main power supply. This means that the equipment uses a separate ground loop that is not connected to the neutral conductor.

The TT system is used for various mobile structures or in places where it is not possible to equip protective grounding in accordance with all standards and norms. Mandatory connection of residual current devices with high-quality grounding is provided (at a voltage of 380 volts, the resistance must be at least 4 ohms). The resistance level must take into account the particular type of circuit breaker.

IT system. A characteristic feature of the circuit is that the neutral conductor of the power source is grounded through electrical appliances or from the ground. Devices must have high resistance, and conductive parts of electrical installations must be grounded using grounding equipment. The high resistance of electrical devices will increase the reliability of the system.

IT is used infrequently, usually for electrical equipment in special buildings (for example, uninterrupted power supply system block PC, emergency lighting of hospitals), where the requirement for reliability and safety is increased. Each of these systems has its own advantages and disadvantages. In this regard, it is necessary to correctly select the protective earthing installation scheme for specific situations.

How TN works

In accordance with the norms of the Electrical Installation Rules (PUE), the TN system is the most reliable. The principle of its operation allows to provide reliable protection of a person and connected electrical equipment from stray currents.

The main condition for safe and reliable operation TN systems - the value of the current between the phase conductor and the bare part in the event of a short circuit in the electrical network must necessarily exceed the value of the current at which the protective devices must operate. For this system, it also becomes necessary to connect a residual current device and differential circuit breakers.

Video "Advanced Grounding System"

We arrange a grounding system

If you decide to make a grounding loop yourself, then you must use ordinary ferrous metal for the grounding structure. For this, iron corners, steel strips, pipes and other structures are suitable. Such material has optimal resistance and low cost. Before starting installation work, you need to draw up a project that will contain a description of the design, material used, dimensions, location of technical communications, type of soil and other parameters.

Be sure to know in what type of soil the ground loop will be installed. This will determine the level of resistance. So in sandy soil, the resistance is much higher than in ordinary earth. The resistance will be affected by soil moisture and the presence of groundwater. The humidity of the earth will vary depending on the climate of the area where the installation work will be carried out.

Scheme and installation

Electrical engineers strongly recommend the use of ready-made schemes for the installation of grounding structures. Ready-made equipment can be purchased in specialized stores. The earthing kit is accompanied by a corresponding connection and installation diagram. The set is certified and has a guarantee for operation. But such a design can be done independently. The most common grounding structures are in the form of a triangle and a square. The first way is more economical.

At the place where the protective structure will be installed, you need to draw a conditional equilateral triangle. Its peaks should be at a distance of 1.5 m from each other. A trench is dug along the contour with a depth of 1 m. At the peaks, 3 main conductors will be clogged - round fittings (diameter - from 35 mm, length - 2-2.5 m). The reinforcement is hammered into the ground, then they must be connected with a metal tire (width - 40 mm, thickness - 4 mm). Fastening is carried out by welding. The ground wire will extend from the structure to the switchboard.

Then the trench is buried. After finishing installation work you need to check the ground loop. For this, special equipment is used, which allows you to measure the resistance in certain areas of the earth (up to 15 meters from the grounding structure). At correct installation resistance will not exceed 4 ohms. At higher values, you need to double-check the connection points. A multimeter will not work for testing.

Almost every house is equipped with grounding. Its task is to ensure safety when using electrical installations by a person. Among professionals, it is customary to divide grounding systems into several types. We will talk about the existing options in our article.

In the world field of electricity, it is customary to classify grounding into three types, and they can be defined using the abbreviation TT, TN, IT. Each letter has the following meaning:

• T - grounding, translated from the French word terra - soil;
• N is neutral, which means this system nulled;
• I - indicates the presence of ground electrode insulation.

Important! The location of the letters of the grounding systems plays important role and bears a certain designation.

The meaning of the first letter indicates the principle of grounding the power supply, the designation of the second letter in the system indicates the grounding of conductive exposed parts of electrical equipment. The last letters speak of the functionality of the neutral and protective conductors.

Grounding systems for a private house

Let's take a closer look at grounding options, each of which will be given a separate section.

Grounding TN and its subspecies

A lot has already been said about grounding systems, but few people pay attention to decoding. When creating the protection of electrical equipment, it is necessary to take into account every detail, because subsequently problems often arise during the repair or reconstruction of the system.

This variety differs from the rest in that it has a grounded neutral. This installation provides for the connection of exposed conductive parts to the zero point of the supply source. You will probably ask what is a "deeply grounded neutral". In general terms, this concept is the connection of a neutral conductor directly to an earth conductor in a transformer installation.

Electrical safety in this system is achieved by exceeding the voltage of the open part of the installation and the "phase" over the value of the operation of the electrical potential for a specific time.

TT earthing system: detailed characteristic

This type of grounding differs from the previous scheme in that it has a "ground" on the neutral wire, while the exposed conductive parts of the electrical equipment are directly connected to the protection system. The TT system provides for a separate installation of the ground loop. This type of protection is used in modern conditions for change houses, mobile and portable constructions.

Grounding systems for an apartment building

Important! When designing this earthing system, a residual current device (RCD) must be used.

Grounding structure IT

IT grounding is used much less frequently than in previous systems. You can find such equipment in buildings for special purposes and industrial enterprises. Mainly installed for emergency lighting.

The design is characterized by the presence of an insulated neutral of the power source from the "ground". In some cases, it is possible to ground it through consumer devices.

Important! It is necessary to use the IT grounding system only in conditions of increased energy security requirements.

What method is used to make the grounding system?

Grounding system diagram

To date, several technologies have been registered that provide for the installation of common grounding systems. Two methods are widely used, which we will now analyze.

1. The standard technique is characterized by the implementation of the grounding structure using ferrous metallurgy raw materials. Initially, a project is being developed, and after preparing all the tools, they begin to implement the contour on the ground. This takes into account a number of factors that can affect the design. The use of this technology has improved over the years and is now used in many climates.
2. Modular grounding involves the use of a special kit, which can be found at retail outlets. In this case, factory-made materials are used.

Installation and raw materials for modular grounding

To install this type of device, use: steel rods with copper-plated parts, couplings and connecting parts, a kit for a modular ground electrode system (brass, copper and copper-plated parts), steel tips, anti-corrosion paste, protective tape. When we have prepared the material, we follow the installation rules:

What are the types of grounding systems

• First of all, a vertical steel rod is installed on the ground;
• The intermediate resistance is measured;
• The remaining steel rods are being installed;
• At this stage, a horizontal grounding conductor is laid;
• All structural elements are connected using terminals or welded equipment, covered with a protective tape. Also, do not forget about anti-corrosion treatment.

Attention! Fulfilling

The most important part of the design, installation and further operation of equipment and electrical installations is a properly executed grounding system. Depending on the grounding structures used, grounding can be natural or artificial. Natural grounding conductors are represented by various metal objects permanently in the ground. These include fittings, pipes, piles and other structures capable of conducting current.

But the electrical resistance and other parameters inherent in these objects cannot be accurately controlled and predicted. Therefore, with such grounding, it is impossible to operate any electrical equipment normally. Regulatory documents provide only artificial grounding using special grounding devices.

Classification of grounding systems

Depending on the schemes of electrical networks and other operating conditions, grounding systems are used TN-S, TNC-S, TN-C, TT, IT, designated in accordance with international classification. The first character indicates the grounding parameters of the power supply, and the second letter character corresponds to the grounding parameters of open parts of electrical installations.

Letter designations are deciphered as follows:

• T (terre - earth) - means grounding,
• N (neuter - neutral) - connection to the source neutral or neutral,
• I (isole) corresponds to isolation.

Zero conductors in GOST have the following designations:

• N - is the zero working wire,
• PE - zero protective conductor,
• PEN - combined zero working and protective earth wire.

TN-C earthing system

Grounding TN refers to systems with solidly grounded neutral. One of its varieties is the TN-C grounding system. It combines functional and protective neutral conductors. The classic version is represented by a traditional four-wire circuit, in which there are three phase and one neutral wire. It is used as the main ground bus, connected to all conductive exposed parts and metal parts, using additional neutral wires.

The main disadvantage of the TN-C system is the loss of protective qualities when the neutral conductor burns out or breaks. This leads to the appearance of life-threatening voltage on all surfaces of device and equipment cases where insulation is not available. The TN-C system does not have a PE protective earth conductor, so all connected sockets are also not earthed. In this regard, for all electrical equipment used, a device is required - connecting the body parts to the neutral wire.

In case of touch phase wire open parts of the housing, a short circuit will occur and the automatic fuse will trip. Fast emergency shutdown eliminates the risk of fire or electric shock to people. It is strictly forbidden to use additional potential equalization circuits in bathrooms when using the TN-C grounding system.

Despite the fact that tn-c circuit is the most simple and economical, it is not used in new buildings. This system has been preserved in the houses of the old housing stock and in street lighting, where the probability of electric shock is extremely low.

Grounding scheme TN-S, TN-C-S

A more optimal, but expensive scheme is the TN-S grounding system. To reduce its cost, practical measures have been developed to take full advantage of this scheme.

The essence of this method lies in the fact that when electricity is supplied from a substation, a combined zero conductor PEN is used, which is connected to a solidly grounded neutral. At the entrance to the building, it is divided into two conductors: zero protective PE and zero working N.

The tn-c-s system has one significant drawback. If the PEN conductor burns out or is damaged in any other way in the section from the substation to the building, a dangerous voltage arises on the PE wire and the parts of the instrument case associated with it. Therefore, one of the requirements of regulatory documents to ensure the safe use of the TN-S system is special measures to protect the PEN wire from damage.

TT earthing scheme

In some cases, when electricity is supplied through traditional overhead lines, it becomes quite problematic to protect the combined PEN earth conductor when using a TN-C-S scheme. Therefore, in such situations, a TT grounding system is used. Its essence lies in the deaf grounding of the neutral of the power source, as well as the use of four wires to transmit three-phase voltage. The fourth conductor is used as functional zero N.

The connection of the modular pin ground electrode system is most often carried out by the consumers. Further, it is connected to all protective earthing conductors PE associated with the parts of the instrument and equipment cases.

The TT scheme has been used relatively recently and has already proven itself in private country houses. In cities, the TT system is used at temporary facilities, such as retail outlets. This method of grounding requires the use of protective devices in the form of RCDs and the implementation of technical measures to protect against thunderstorms.

IT grounding system

The systems with a dead-earthed neutral considered earlier, although they are considered quite reliable, however, have significant drawbacks. Much safer and more perfect are circuits with a neutral completely isolated from the ground. In some cases, devices and devices with significant resistance are used to ground it.

Similar circuits are used in the IT earthing system. They are the best way suitable for medical facilities, while maintaining uninterrupted power to life support equipment. IT schemes have proven themselves well in energy and oil refineries, and other facilities where complex highly sensitive devices are available.

The heart of the IT system is the isolated source neutral I and T installed on the consumer side. The supply of voltage from the source to the consumer is carried out using a minimum number of wires. In addition, all conductive parts present on the equipment cases installed at the consumer are connected to the ground electrode. In the IT system, there is no zero functional conductor N in the section from the source to the consumer.

Thus, all grounding systems TN-C, TN-S, TNC-S, TT, IT ensure reliable and safe operation of devices and electrical equipment connected to consumers. The use of these circuits prevents electric shock to people using the equipment. Each system is used in specific conditions, which must be taken into account in the design process and subsequent installation. Due to this, guaranteed safety, preservation of health and life of people is ensured.

My story will be in three parts.
1 part. Grounding (general information, terms and definitions).
2 part. Traditional ways construction of grounding devices (description, calculation, installation).
3 part. Modern methods of construction of grounding devices (description, calculation, installation).

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, it is better for him to skip the first part and start reading from the second part.

If the reader has the necessary knowledge and wants to get acquainted only with new products, it is better to skip the first two parts and go straight 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 the terminology, the main types of grounding and the qualitative characteristics of grounding devices.

A. Terms and definitions
B. Purpose (types) of grounding
B1. Working (functional) grounding
B2. Protective earth
B2.1. Grounding as part of external lightning protection
B2.2. Grounding as part of an overvoltage protection system (SPD)
B2.3. Grounding in the electrical network
B. Grounding quality. Ground resistance.
IN 1. Factors affecting the quality of grounding
B1.1. The area of ​​contact of the earth electrode with the ground
B1.2. Soil electrical resistance (specific)
IN 2. Existing regulations ground resistance
IN 3. Ground resistance calculation

A. Terms and definitions
To avoid confusion and misunderstanding in the future story, I will start from this point.
I will give the established definitions from the current document “Electrical Installation Rules (PUE)” in latest edition(chapter 1.7 in the edition of the seventh edition).
And I will try to “translate” these definitions into “simple” language.

grounding- deliberate electrical connection any point of the network, electrical installation or equipment with a grounding device (PUE 1.7.28).
The soil is a medium that has the property of “absorbing” an electric current. Also, it is a certain “common” point in the electrical circuit, relative to which the signal is perceived.

A set of grounding conductor / grounding conductors and grounding conductors (PUE 1.7.19).
This is a device/circuit consisting of a grounding conductor and a grounding conductor connecting this grounding conductor to the grounded part of the network, electrical installation or equipment. May be distributed, i.e. consist of several mutually distant ground electrodes.

It is shown in the figure with thick red lines:

A conductive part or a set of interconnected conductive parts that are in electrical contact with the ground (PUE 1.7.15).
The conductive part is a metal (conductive) element / electrode of any profile and design (pin, pipe, strip, plate, mesh, bucket :-), etc.), located in the ground and through which an electric current “flows” into it from the electrical installation.
The configuration of the grounding conductor (number, length, location of electrodes) depends on the requirements for it, and the ability of the soil to “absorb” the electric current flowing / “flowing” from the electrical installation through these electrodes.

In the figure, it is shown with thick red lines:

Ground resistance- the ratio of the voltage on the grounding device to the current flowing from the grounding conductor into the ground (PUE 1.7.26).
Ground resistance is the main indicator of a grounding device, which determines its ability to perform its functions and determines its quality as a whole.
The grounding resistance depends on the area of ​​electrical contact of the grounding electrode (grounding electrodes) with the ground (“drainage” of current) and the specific electrical resistance of the soil in which this grounding conductor is mounted (“absorption” of current).

Conductive part in electrical contact with local ground (GOST R 50571.21-2000 p. 3.21)
I repeat: a conductive part can be a metal (conductive) element of any profile and design (pin, pipe, strip, plate, mesh, bucket :-), etc.), located in the ground and through which it “flows” into it electric current from the electrical installation.

In the figure, they are shown with thick red lines:

- “popular” name of a grounding conductor or grounding device, consisting of several grounding electrodes (a group of electrodes) connected to each other and mounted around an object along its perimeter/contour.

In the figure, the object is indicated by a gray square in the center,
and the ground loop - thick red lines:

Specific electrical resistance of soil- a parameter that determines the level of "electrical conductivity" of the soil as a conductor, that is, how well the electric current from the ground electrode will spread in such an environment.
This is a measurable value that depends on the composition of the soil, dimensions and density.
adhering to each other of its particles, humidity and temperature, the concentration of soluble chemicals in it (salts, acid and alkaline residues).

B. Purpose (types) of grounding
Grounding is divided into two main types according to the role performed - into working (functional) and protective. also in various sources additional types are given, such as: “instrumental”, “measuring”, “control”, “radio”.

B1. Working (functional) grounding
This is the grounding of a point or points of the current-carrying parts of an electrical installation, performed to ensure the operation of the electrical installation (not for electrical safety purposes) (PUE 1.7.30).

Working grounding (electrical contact with the ground) is used for the normal operation of an electrical installation or equipment, i.e. to operate in NORMAL mode.

B2. Protective earth
This is a grounding performed for electrical safety purposes (PUE 1.7.29).

Protective grounding provides protection for electrical installations and equipment, as well as protection of people from exposure to dangerous voltages and currents that may occur in case of breakdowns, improper operation of equipment (i.e. in EMERGENCY mode) and lightning strikes.
Also, protective grounding is used to protect equipment from interference during switching in the supply network and interface circuits, as well as from electromagnetic interference induced from equipment operating nearby.

The protective purpose of grounding can be considered in more detail in two examples:
as part of an external lightning protection system in the form of a grounded lightning rod
as part of a surge protection system
as part of the facility's power grid

B2.1. Grounding as part of lightning protection
Lightning is a discharge or, in other words, a “breakdown” that occurs FROM the cloud TO the ground, when a charge of a critical value accumulates in the cloud (relative to the ground). Examples of this phenomenon on a smaller scale are "breakdown" in a capacitor and gas discharge in a lamp.

Air is a medium with very high resistance (dielectric), but the discharge overcomes it, because. has great power. The discharge path follows areas of least resistance, such as water droplets in the air and trees. This explains the root-like structure of lightning in the air and the frequent hitting of lightning in trees and buildings (they have less resistance than the air in this gap).
When it hits the roof of a building, lightning continues its way to the ground, also choosing areas with the least resistance: wet walls, wires, pipes, electrical appliances - thus posing a danger to people and equipment located in this building.

Lightning protection is designed to divert the lightning discharge from the protected building/object. A lightning discharge, following the path of least resistance, hits a metal lightning rod above the object, then descends to the ground along the metal lightning rods located outside the object (for example, on the walls), where it diverges in it (I remind you: the soil is a medium that has the property of “absorbing ” into itself an electric current).

In order to make lightning protection "attractive" for lightning, as well as to exclude the spread of lightning currents from lightning protection parts (receiver and outlets) inside the facility, its connection to the ground is made through a ground electrode with low ground resistance.

Grounding in such a system is a mandatory element, because. it is it that ensures the complete and rapid transition of lightning currents into the ground, preventing their propagation throughout the facility.

B2.2. Grounding as part of a surge protection system (SPD)
The SPD is designed to protect electronic equipment from the charge accumulated in any section of the line/network as a result of exposure to an electromagnetic field (EMF) induced from a nearby powerful electrical installation (or high-voltage line) or EMF that occurred during a close (up to hundreds of meters) discharge lightning.

A striking example of this phenomenon is the accumulation of charge on the copper cable of the house network or on the "forwarding" between buildings during a thunderstorm. At some point, the devices connected to this cable (computer network card or switch port) cannot withstand the “size” of the accumulated charge and an electrical breakdown occurs inside this device, destroying it (simplified).
To “bleed” the accumulated charge parallel to the “load”, an SPD is placed on the line in front of the equipment.

A classic SPD is a gas discharger designed for a certain “threshold” of charge, which is less than the “safety margin” of the protected equipment. One of the electrodes of this arrester is grounded, and the other is connected to one of the wires of the line/cable.

When this threshold is reached, a discharge occurs inside the spark gap:-) between the electrodes. As a result, the accumulated charge is discharged into the ground (through grounding).

As in lightning protection, grounding in such a system is a mandatory element, because. it is this that ensures the timely and guaranteed occurrence of a discharge in the SPD, preventing the charge on the line from exceeding a level that is safe for the protected equipment.

B2.3. Grounding in the electrical network
The third example of the protective role of grounding is to ensure the safety of humans and electrical equipment in case of breakdowns / accidents.

The easiest way to describe such a breakdown is by shorting the phase wire of the mains to the device case (short circuit in the power supply or short circuit in the water heater through the aquatic environment). A person who touches such a device will create an additional electrical circuit, through which a current will run, causing damage to internal organs in the body - primarily nervous system and hearts.

To eliminate such consequences, the connection of housings with a ground electrode is used (to divert emergency currents into the ground) and protective automatic devices that cut off the current in a split second in an emergency.

For example, grounding of all cases, cabinets and racks of telecommunications equipment.

B. Grounding quality. Ground resistance.
For the correct performance of its functions by grounding, it must have certain parameters / characteristics. One of the main properties that determine the quality of grounding is the current spreading resistance (grounding resistance), which determines the ability of the grounding electrode (grounding electrodes) to transmit currents coming to it from the equipment into the ground.
This resistance has finite values ​​and ideally is zero, which means that there is no resistance when passing "harmful" currents (this guarantees their FULL absorption by the ground).

The resistance mainly depends on two conditions:
area (S) of the electrical contact of the earth electrode with the ground
electrical resistance (R) of the soil itself, in which the electrodes are located

B1.1. The area of ​​contact of the earth electrode with the ground.
The larger the area of ​​contact of the ground electrode with the ground, the greater the area for the current to pass from this ground electrode to the ground (the more favorable conditions are created for the current to pass into the ground). This can be compared to the behavior car wheel on the turn. A narrow tire has a small area of ​​contact with asphalt and can easily begin to slide on it, “sending” the car into a skid. A wide tire, and even a little deflated, has a much larger contact area with asphalt, providing reliable traction with it and, therefore, reliable control over the movement.

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 grounding devices used in the calculations).

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 ground resistance standards
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 Ohms.

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 for overhead communication lines (for example, a local area network based on 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 single-phase current source (PUE 1.7.101)
at the ground used to connect lightning rods, the resistance should be no more than 10 ohms (RD 34.21.122-87, p. 8)
for private houses, with connection to the mains 220 Volt / 380 Volt:
when using the TN-C-S system, 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 high operator training.
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”. The formulas are substituted with the average values ​​of soil resistivity, or their highest 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.

As vertical electrodes, almost always choose steel pipes, pins / rods, angles, etc. standard rolled products having a large length (more than 1 meter) with relatively small transverse dimensions. This choice is associated with the possibility of easy penetration of such elements into the ground, in contrast to, for example, a flat sheet.

More about construction in the following sections.

Alexey Rozhankov, technical specialist.

In preparing this article, the following materials were used:
Rules for the Construction of Electrical Installations (PUE), part 1.7 as amended by the seventh edition
GOST R 50571.21-2000 (IEC 60364-5-548-96)
Grounding devices and systems for equalizing electrical potentials in electrical installations containing information processing equipment (google)
Instructions for the installation of lightning protection of buildings and structures RD 34.21.122-87
Publications on the site ""
Own experience and knowledge