Requirements for protective grounding and grounding devices. What is protective grounding and grounding? Important! How not to organize protective grounding

To ensure the protection of people when touching metal non-current-carrying parts that may for some reason be energized, along with other means, protective grounding and grounding are used.

According to GOST 12.1.009-76 “System of occupational safety standards. Electrical safety. Terms and definitions" protective grounding - intentional electrical connection with earth or its equivalent of metal non-current-carrying parts that may become live. The purpose of protective grounding is to eliminate the danger of injury to people electric shock when voltage appears on structural parts of electrical equipment, i.e. when there is a short circuit to the housing.

Metal non-current-carrying parts of electrical equipment are subject to protective grounding, which, due to faulty insulation, may be energized and which can be touched by people and animals.

The operating principle of protective grounding is to reduce the voltage between the energized housing and the ground to a safe value.

It should be noted that in the technical code of established practice “Electrical installations for voltages up to 750 kV. Overhead power lines and conductors, distribution devices and transformer substations, electric power and battery installations, residential electrical installations public buildings. Rules for design and protective measures for electrical safety. Electricity metering. Acceptance testing standards”, approved by Resolution of the Ministry of Energy of the Republic of Belarus dated August 23, 2011 No. 44, defines not only the term “grounding”, but also terms derived from it:

grounding - an intentional electrical connection of any point in the network, electrical installation or equipment with a grounding device;

protective grounding - grounding performed for electrical safety purposes;

functional grounding (working, technological) - grounding of a point or points of a system, or installation, or electrical equipment for purposes other than electrical safety.

According to GOST 12.1.009-76 “System of occupational safety standards. Electrical safety. Terms and definitions “grounding” is an intentional electrical connection with a neutral protective conductor of metal non-current-carrying parts that may be energized.

The purpose of grounding is to eliminate the danger of electric shock to people in the event of a breakdown on the housing.

The operating principle of grounding is the transformation of a short circuit to the housing into a single-phase short circuit (i.e., a short circuit between phase and neutral wires) in order to cause a large current capable of triggering the protection and thereby automatically disconnecting the damaged installation from the supply network. Such protection can be fuses, magnetic starters with built-in thermal protection, contactors in combination with thermal relays, circuit breakers that simultaneously provide protection against currents short circuit and from overload.

Metal structural non-current-carrying parts of electrical equipment that must be grounded are subject to grounding: the housings of machines, devices, etc. In a network with grounding, the receiver housing cannot be grounded without connecting it to the neutral protective wire.

For safe work On various electrical installations and conductors, the connection of open metal taps to the ground and the network connection to the neutral cable are used. But few novice craftsmen know exactly the difference between grounding and neutralizing electrical installations and electrical equipment.

Definition of grounding

Grounding is the intentional connection of open parts electrical equipment, which are energized, to a special grounding tap, bus or other protective equipment. This could be reinforcement in the ground, part of an electrical installation or other devices. This approach, according to the PUE, is a mandatory measure of deliberate protection of both residential and non-residential assets. This is also stated in the rules and requirements of GOST 12.1.030-81 SSBT (electrical safety and system of occupational safety standards).

In almost every modern house circuit installed grounding TN-C-S or TN-S. But in old buildings there is often no grounding at all, so apartment owners in such buildings have to organize the ground on their own. This system is called TN-C. This is done by connecting the tap to the grounding loop, which can be located directly in the ground near the building or near the transformer booth.

Figure TN-C

Theoretically, such a wiring upgrade could be organized by a special installation company, but this is rarely practiced. More often, ground is supplied to the panel on the floor (in an apartment building), and the remaining wires are connected to it.

1. If a phase hits an open metal tap of any electrical device, then voltage appears in it. The same happens if, for example, the cable insulation is broken. The human body is an excellent conductor of current; if you touch such a tap, you will receive swipe electric shock Grounding will help avoid this;
2. Stray currents go into the grounding conductor, this guarantees life protection;
3. Particularly dangerous is the voltage that reaches heating radiators. In this case, all batteries in the house become current conductors. But if the ground is installed, then all the voltage will go through the conductor.

If it is not possible to establish a full grounding circuit, then other methods are used. For example, it is now very common to connect portable grounding pins (portable busbars). Their operation is no different from a standard stationary outlet, but at the same time they are much more practical in their functionality.

Zeroing purpose

Grounding and grounding are sometimes confused with each other, so what is the difference between the two? Zeroing is applied according to the PUE only for industrial installations and is not a guarantee of safety. If a phase hits the open part of the device, then the current does not flow out. After this, the two phases are paired, and, as a result, a short circuit occurs. The neutral conductor is necessary for rapid response differential circuit breaker for a short circuit, but not to protect a person from electric shock. Therefore, it is customary to use it only in production, where a quick power shutdown is required in case of emergency situation.

Is it necessary to do grounding in a private house or apartment? No, this is not necessary, and is even fraught with various negative consequences. Say, if the neutral wire burns out, then a larger number electrical devices, to which it was connected will break due to the extremely high voltage surge. It is worth remembering that your safety will not be affected if, along with grounding, you also arrange grounding, install an RCD and a safety switch.

How to set the grounding so that the device connected to it does not burn out:

1. You must use three-core insulated wire. One core is allocated for phase, the second for zero, the third for grounding;
2. Ground connects at the very end electrical installation work to the body of the safe conductor to the grounding loop, etc. The most practical is a special grounding tap at the switchboard;
3. For safety reasons, various power switches and other protective settings must be installed.

Video: what is the difference between grounding and grounding

Main difference

The most important thing to remember: grounding and grounding circuits have different protective effect. Zero guarantees a quick response to potential changes or current leakage for protection installations. Accordingly, when high voltage All energy consumers are switched off: lighting fixtures, computers and other machines (including machine tools, transformers).

Grounding ensures potential equalization and protection against electric shock. Earth is more often used at home; its installation can be easily done with your own hands. But there is no guarantee that the fuses will quickly respond to a leak. The best option to increase the safety guarantee is the combined use of grounding and grounding of networks and open parts of machines.

Before installing any of these protection options, you must obtain permission to carry out the work. Additionally, the protective conductor is calculated, earth is connected to each consumer in the home, and protective equipment is installed.

Even people are confused about the purpose and installation of these methods of protection against electric shock. professional electricians. This is not the case for everyone, but there are precedents. But a basic understanding of terms sometimes saves dozens of lives. Even if we are not talking about electric shock, but about the commissioning of a new private house. If the protection is performed incorrectly, the controlling organization will not allow voltage to be supplied to the input panel. And rightly so, no one wants to take responsibility for people’s lives. Today we will figure out what the terms and nullification mean, what is the difference between them, and when it is possible to use one or another method of protection.

In accordance with GOST 12.1.009–76:

• protective grounding- this is the intentional electrical connection to the ground or its equivalent of metallic non-current-carrying parts that may be energized;
• zeroing- this is an intentional electrical connection with a neutral protective conductor of metal non-current-carrying parts that may be energized.

GOST R 50571.2–94 “Electrical installations of buildings. Part 3. Main characteristics" provides a classification of grounding systems for electrical networks: IT, TT, TN-C, TN-C-S, TN-S.

According to the PUE, grounding is mandatory (if there is a circuit or the possibility of installing it). All metal enclosures that could hypothetically become energized must be grounded. If there is no possibility of grounding, protective grounding is carried out with the mandatory installation of devices protective shutdown(RCD) and automatic in incoming electrical.

Of course, the language in which PUE and GOST are written can be difficult for a person without electrical engineering education, which means it is worth examining in detail what grounding and grounding are in ordinary language that is understandable to the common man.

What is grounding: how it works, the principle of operation and the advantages of such protection

The principle of grounding is to prevent the passage of electric current through the human body if, due to any circumstances, the body becomes energized. This can happen if the cable insulation is damaged. Let's look at an example. A core with damaged insulation is in contact with a metal casing. The housewife, while preparing food in the kitchen, touches something that is not grounded. This causes current to rush to the ground, using the human body as a conductor. The result can be very disastrous, even death.

Now let's look at why grounding is needed and how it works. The same example, but using protection. The most stringent grounding requirements apply. When taking measurements, the circuit resistance should be practically absent, which allows the current to flow freely into the ground along the bus. The laws of physics do not allow voltage to flow through the human body, which has its own resistance. Some have more, others have less, but its presence is not disputed. It turns out that the current flows along the path of least resistance, through the ground electrode. If an RCD is included in the circuit, it will detect a leak and turn off the power supply to the device.

What is grounding of electrical appliances: application possibilities

Protective grounding electrical appliances is used if it is impossible to install grounding. This situation may arise if an apartment building was built in Soviet times. Such houses do not have their own outline, and it will not be possible to arrange one on your own.

Protective grounding is a system that performs a different job from grounding. If the second is designed to divert the voltage to the ground, eliminating the possibility of electric shock, then the first is carried out with the aim of creating (if the insulation breaks down and hits the housing) a short circuit. In this case, the automation is triggered and the electricity is turned off.

Important information! IN apartment buildings modern construction and in private sectors, installation of grounding is prohibited these days. This is dictated by the safety of residents. Automation can fail, which will lead to irreparable consequences.

Protective grounding requires correct installation. You should not think that it is enough to throw a jumper from the neutral contact inside to the ground one. This is strictly prohibited. Let's consider a situation when an already “burnt” zero is subjected to a short circuit load, and the machine has not yet had time to operate. The zero burns out, eliminating the short circuit, but the device remains energized. A person, hoping for the absence of electricity (after all, there is no light, the zero has burned out), moves towards the exit by touch and leans on the body, which is under voltage. The outcome is clear, isn't it?

Grounding and grounding: what is the difference

The difference between these systems is in the method of implementing protection. When installing protective grounding, the role of a voltage cut-off device in the event of an emergency situation is assumed by the RCD, and in the case of installation of grounding, the RCD becomes powerless; only the automatic device can operate. Why is this happening? The residual current device reacts only to current leaks, completely ignoring any overloads, including short circuits. If a grounding is installed and an RCD is included in the circuit without a circuit breaker, in the event of a short circuit the RCD does not operate, but simply burns out without disconnecting the voltage from the line.

What is the difference between grounding and grounding: generalization

Grounding differs from grounding in the method of protection and installation. Such systems contradict each other, which means installing a circuit that includes both options is unacceptable. Zeroing is installed only in apartment buildings that are not equipped with their own circuit. In other cases, such installation is prohibited. Now let's talk in more detail about the methods of its construction.

What is zeroing and how to arrange it correctly

The installation diagram looks like this: The neutral arriving at the input machine is bifurcated, each of the cores goes to a separate bus. One of the buses becomes zero, and the second becomes grounding. From the neutral bus, the conductors go through the automation and further to all zero contacts of the apartment's consumers. Grounding connects to the housing input panel, the yellow-green wire from it goes to the corresponding contacts of the sockets and that require it. Contact of the ground wire with the neutral wire after protective automation forbidden.

Important information! Improper installation of protective grounding leads to burnout of cable cores and a fire. Electric shock and even death are also possible.

The best protection option is a grounding device?

The only correct answer to this question is yes. This is true. , mounted according to all the rules, will protect a person much better than the previous version. You can improve your protection by using additional devices– circuit breakers, RCDs or automatic circuit breakers. After all, what is protective grounding? At its core, it is a system for discharging electric current in the event of an accident to a place where it cannot harm a person.

Regarding the grounding device, we can say that it can be different - a grounding loop around the perimeter of the building, a “triangle” in the yard, or a natural grounding device. We will definitely consider all the rules and methods of its installation in one of the upcoming topics. But for general information It makes sense to understand the definition of what is a natural grounding agent.

Good to know! As a natural grounding agent, you can use any metal constructions located underground, with the exception of fuel and lubricants pipelines, sewage systems and objects coated with anti-corrosion compounds. Water pipes can be used for this purpose.

Generally speaking, it can be noted that the great and terrible power of electricity has long been described, calculated, and entered into thick tables. Normative base, defining the paths of sinusoidal electrical signals frequencies of 50 Hz can plunge any neophyte into horror with its volume. And, despite this, any regular on technical forums has long known that there is no more scandalous issue than grounding.

The mass of conflicting opinions does little to establish the truth. Moreover, this issue is actually serious and requires closer consideration.

Basic Concepts

If we omit the introduction of the “electrician’s bible” (), then to understand grounding technology you need to turn (to begin with) to Chapter 1.7, which is called “Grounding and protective measures for electrical safety”.

In clause 1.7.2. PUE says:

Electrical installations with regard to electrical safety measures are divided into:

• electrical installations above 1 kV (with high currents ground fault), ;
• electrical installations above 1 kV in networks with an isolated neutral (with low ground fault currents);
• electrical installations up to 1 kV with a solidly grounded neutral;
• electrical installations up to 1 kV with insulated neutral.

The vast majority of residential and office buildings in Russia use solidly grounded neutral. Clause 1.7.4. reads:

A solidly grounded neutral is the neutral of a transformer or generator, connected to a grounding device directly or through low resistance (for example, through current transformers).

The term is not entirely clear at first glance - neutral and grounding devices are not found at every turn in the popular science press. Therefore, below all unclear places will be gradually explained.

Let's introduce a few terms - this way we can at least speak the same language. Perhaps the points will seem "taken out of context". But not fiction, and such separate use should be completely justified - like the application of individual articles of the Criminal Code. However, the original PUE is quite accessible both in bookstores and online - you can always turn to the original source.

• 1.7.6. Grounding of any part of an electrical installation or other installation is the intentional electrical connection of this part to a grounding device.
• 1.7.7. Protective grounding is the grounding of parts of an electrical installation in order to ensure.
• 1.7.8. Working grounding is the grounding of any point of live parts of an electrical installation, which is necessary to ensure the operation of the electrical installation.
• 1.7.9. Grounding in electrical installations with voltage up to 1 kV is called intentional connection parts of the electrical installation that are not normally energized, with a solidly grounded neutral of the generator or transformer in the networks three-phase current, with solidly grounded source output single-phase current, with a solidly grounded midpoint of the source in networks direct current.
• 1.7.12. A grounding electrode is a conductor (electrode) or a set of metallic interconnected conductors (electrodes) that are in contact with the ground.
• 1.7.16. A grounding conductor is a conductor that connects the grounded parts to the ground electrode.
• 1.7.17. A protective conductor (PE) in electrical installations is a conductor used to protect people and animals from electric shock. In electrical installations up to 1 kV protective conductor, connected to the solidly grounded neutral of the generator or transformer, is called the neutral protective conductor.
• 1.7.18. The neutral working conductor (N) in electrical installations up to 1 kV is the conductor used to power electrical receivers, connected to a solidly grounded neutral of a generator or transformer in three-phase current networks, to a solidly grounded terminal of a single-phase current source, to a solidly grounded source point in three-wire DC networks. A combined neutral protective and neutral working conductor (PEN) in electrical installations up to 1 kV is a conductor that combines the functions of a neutral protective and neutral working conductor. In electrical installations up to 1 kV with a solidly grounded neutral, the neutral working conductor can serve as a neutral protective conductor.

Rice. 1. Difference between protective grounding and protective “zero”

So, a simple conclusion follows directly from the terms of the PUE. The differences between “ground” and “zero” are very small... At first glance (how many copies are broken in this place). At the very least, they must be combined (or even can be done “in one bottle”). The only question is where and how it is done.

In passing, we note paragraph 1.7.33.

Grounding or grounding of electrical installations should be performed:

• at voltage 380 V and above alternating current and 440 V and above direct current - in all electrical installations (see also 1.7.44 and 1.7.48);
• at rated voltages above 42 V, but below 380 V AC and above 110 V, but below 440 V DC - only in hazardous areas, especially hazardous and in outdoor installations.

In other words, it is not at all necessary to ground or neutralize a device connected to a voltage of 220 volts AC. And there is nothing particularly surprising in this - there is really no third wire in ordinary Soviet sockets. We can say that the Eurostandard, which is coming into its own in practice (or the new edition of the PUE, which is close to it) is better, more reliable, and safer. But according to the old PUE, people lived in our country for decades... And what is especially important, houses were built in entire cities.

However, when it comes to grounding, it's not just about the supply voltage. A good illustration of this is VSN 59-88 (State Committee for Architecture) “Electrical equipment of residential and public buildings. Design standards” Excerpt from Chapter 15. Grounding (grounding) and protective safety measures:

15.4. For grounding (grounding) metal cases of household air conditioners, stationary and portable household appliances class I (not having double or reinforced insulation), household electrical appliances powerSt. 1.3 kW, housings of three-phase and single-phase electric stoves, digesters and others thermal equipment, as well as metal non-current-carrying parts technological equipment in rooms with wet processes, a separate conductor with a cross-section equal to the phase one should be used, laid from the switchboard or panel to which this electrical receiver is connected, and in lines supplying medical equipment, from the ASU or main switchboard of the building. This conductor is connected to the neutral conductor of the supply network. The use of a working neutral conductor for this purpose is prohibited.

This results in a normative paradox. One of the visible results at the everyday level was the acquisition washing machines"Vyatka-automatic" with a coil of single-core aluminum wire with the requirement to perform grounding (by the hands of a certified specialist).

And one more interesting point:. 1.7.39. In electrical installations up to 1 kV with a solidly grounded neutral or a solidly grounded output of a single-phase current source, as well as with a solidly grounded midpoint in three-wire DC networkszeroing must be performed. The use of grounding of electrical receiver housings in such electrical installations without grounding them is not allowed.

In practice, this means that if you want to “ground”, first “ground”. By the way, this is directly related to the famous issue of “battery storage” - which, for a completely incomprehensible reason, is mistakenly considered better than zeroing(grounding).

Grounding parameters

The next aspect to consider is numeric parameters grounding. Since physically it is nothing more than a conductor (or many conductors), its main characteristic will be resistance.

1.7.62. Grounding device resistance, kkto which the neutrals of generators or transformers or the terminals of a single-phase current source are connected, at any time of the year there should be no more than 2, 4 and 8 Ohms, respectively, at line voltages of 660, 380 and 220 V of a three-phase current source or 380, 220 and 127 V of a single-phase current source. This resistance must be provided taking into account the use natural grounding agents, as well as grounding conductors for repeated grounding neutral wire Overhead lines up to 1 kV with at least two outgoing lines. In this case, the resistance of the grounding conductor located in close proximity to the neutral of the generator or transformer or the output of a single-phase current source should be no more than: 15, 30 and 60 Ohms, respectively, at line voltages of 660, 380 and 220 V of a three-phase current source or 380, 220 and 127 In a single-phase current source.

For lower voltage, higher resistance is acceptable. This is quite understandable - the first purpose of grounding is to ensure human safety in the classic case of a “phase” hitting the body of an electrical installation. The lower the resistance, the smaller part of the potential may be “on the body” in the event of an accident. Therefore, the hazard for higher voltages must be reduced first.

Additionally, it should be taken into account that grounding also serves for normal operation fuses. To do this, it is necessary that the line upon breakdown"on the body" significantly changed the properties (primarily resistance), otherwise the operation would not occur. The greater the power of the electrical installation (and the consumed voltage), the lower its operating resistance, and accordingly the grounding resistance should be lower (otherwise, in the event of an accident, the fuses will not trip minor change total circuit resistance).

The next standardized parameter is the cross-section of the conductors.

1.7.76. Grounding and neutral protective conductors in electrical installations up to 1 kV must have dimensions no less than those given in table. 1.7.1 (see also 1.7.96 and 1.7.104).

It is not advisable to present the entire table; an excerpt will suffice:

For non-insulated copper, the minimum cross-section is 4 square meters. mm, for aluminum - 6 sq. mm. For isolated ones, respectively, 1.5 sq. mm and 2.5 sq. mm. If the grounding conductors go in the same cable with the power wiring, their cross-sectionThe reduction can be 1 sq. mm for copper, and 2.5 sq. mm for aluminum.

Grounding in a residential building

In a normal “domestic” situation, users of the power grid (i.e. residents) deal only with the Group network ( 7.1.12 PUE. Group network - a network from panels and distribution points to lamps, plug sockets and other electrical receivers). Although in old buildings, where the panels are installed directly in the apartments, they have to deal with part of the distribution network ( 7.1.11 PUE. Distribution network - network from VU, ASU, main switchboard to distribution points and switchboards). It is advisable to understand this well, because often “zero” and “ground” differ only in the place of connection with the main communications.

From this, the first grounding rule is formulated in the PUE:

7.1.36. In all buildings, group network lines are laid from group, floor and apartment panels to general lighting fixturesconnections, plug sockets and stationary electrical receivers must be made with three wires (phase - L, neutral working - N and neutral protective - PE conductors). Combining zero working and zero protective conductors of different group lines is not allowed. The neutral working and neutral protective conductors are not allowed to be connected on panels under a common contact terminal.

Those. from a floor, apartment or group panel you need to lay 3 (three) wires, one of which is a protective zero (not ground at all). Which, however, does not at all prevent it from being used for grounding a computer, cable shield, or the “tail” of lightning protection. It seems that everything is simple, and it is not entirely clear why to delve into such complexities.

You can look at your home outlet... And with a probability of about 80% you will not see the third contact there. What is the difference between zero working and zero protective conductors? In the shield they are connected on one bus (even if not at the same point). What happens if you use the working zero as a protective zero in this situation?

Assuming that a careless electricianphase and zero melt in the shield, it’s difficult. Although this constantly frightens users, it is impossible to make a mistake in any state (although there are unique cases). However, the “working zero” goes along numerous grooves, probably passing through several distribution boxes (usually small, round, mounted in the wall near the ceiling).

It’s much easier to confuse phase with zero there (I’ve done this myself more than once). As a result, there will be 220 volts on the body of the incorrectly “grounded” device. Or even simpler - a contact will burn out somewhere in the circuit - and almost the same 220 will pass to the housing through the load of the electrical consumer (if it is a 2-3 kW electric stove, then it will not seem too small).

For the human protection function, frankly speaking, this is a bad situation. But for connecting grounding, lightning protection type APC is not fatal, since a high-voltage isolation is installed there. However, it would definitely be wrong to recommend this method from a security point of view. Although it must be admitted that this norm is violated very often (and, as a rule, without any adverse consequences).

It should be noted that the lightning protection capabilities of the working and protective zeros are approximately equal. Resistance (to connecting bus) fromvaries slightly, and this is perhaps the main factor influencing the flow of atmospheric interference.

From the further text of the PUE, you can see that literally everything that is in the house must be connected to the neutral protective conductor:

7.1.68. In all rooms it is necessary to connect exposed conductive parts of luminaires general lighting and stationary electrical receivers ( electric stoves, boilers, household air conditioners, electric towels, etc.) to the neutral protective conductor.

In general, it is easier to imagine this with the following illustration:

Rice. 2. Grounding diagram

The picture is quite unusual (for everyday perceptionand I). Literally everything in the house must be grounded to a special bus. Therefore, the question may arise - after all, we lived without this for decades, and everyone is alive and well (and thank God)? Why change everything so seriously? The answer is simple - there are more electricity consumers, and they are becoming more powerful. Accordingly, the risks of damage increase.

But the relationship between safety and cost is statistical, and no one has canceled the savings. Therefore, it is not worth blindly placing a copper strip of a decent cross-section around the perimeter of the apartment (instead of a baseboard), placing everything on it, right down to the metal legs of the chair. How you shouldn’t wear a fur coat in the summer and always wear a motorcycle helmet. This is already a question of adequacy.

Also in the area of ​​an unscientific approach is the independent digging of trenches under the protective contour (in a city house this will obviously bring nothing but problems). But for those who still want to experience all the delights of life - in the first chapter of the PUE there are standards for the manufacture of this fundamental structure (in the very literal sense of the word).

Summarizing the above, we can draw the following practical conclusions:

• If the group network is made of three wires, a protective zero can be used for grounding/zeroing. In fact, that’s what it was invented for.
• If the group network is made of two wires, it is advisable to install a protective neutral wire from the nearest panel. The cross-section of the wire must be larger than the phase one (more precisely, you can check in the PUE).

Introduction

Protective grounding (grounding) is the main measure for protecting metal structures. The main purpose of this measure is to protect the user of the device from possible electric shock if there is a short circuit to the housing in the event, for example, electric shock in the event of a phase wire shorting to when the insulation is broken. In other words, grounding is a backup protective functions fuses. There is no need to ground all electrical appliances in the house: most of them have a reliable plastic case, which itself protects against electric shock. Protective grounding differs from grounding in that the bodies of machines and devices are connected not to the “ground”, but to a grounded neutral wire coming from the transformer substation along a four-wire power line. To ensure complete human safety, the resistance of the grounding conductors (together with the circuit) should not exceed 4 ohms. For this purpose, they are checked twice a year (in winter and summer) by a special laboratory.

Grounding is an intentional electrical connection of any point in an electrical network, electrical installation or equipment, with a grounding device.

The grounding device consists of a ground electrode (a conductive part or a set of interconnected conductive parts that are in electrical contact with the ground directly or through an intermediate conducting medium) and a grounding conductor connecting the grounded part (point) to the ground electrode. The ground electrode can be a simple metal rod (most often steel, less often copper) or a complex set of specially shaped elements. The quality of grounding is determined by the resistance value of the grounding device, which can be reduced by increasing the area of ​​the grounding conductors or the conductivity of the medium - using many rods, increasing the salt content in the ground, etc. Electrical resistance grounding device is determined by the requirements of the PUE

Terminology

· Solidly grounded neutral - the neutral of a transformer or generator, connected directly to the grounding device. The output of a single-phase alternating current source or the pole of a direct current source in two-wire networks, as well as the midpoint in three-wire DC networks, can also be solidly grounded.

· Isolated Neutral- neutral of a transformer or generator, not connected to a grounding device or connected to it through a high resistance of signaling, measuring, protection and other similar devices.

Designations

Designation on diagrams (two symbols on the right)

Protective grounding conductors in all electrical installations, as well as neutral protective conductors in electrical installations with voltages up to 1 kV with a solidly grounded neutral, including busbars, must have letter designation PE (Protective Earthing) and color designation alternating longitudinal or transverse stripes of the same width (for tires from 15 to 100 mm) of yellow and green colors. Zero working (neutral) conductors are designated by the letter N and blue. Combined neutral protective and neutral working conductors must have the letter designation PEN and a color designation: blue along the entire length and yellow-green stripes at the ends.

Grounding system designations

The first letter in the designation of the grounding system determines the nature of the grounding of the power source:

· T - direct connection of the neutral of the power source to the ground;

· I - all live parts are isolated from the ground.

The second letter determines the state of exposed conductive parts relative to ground:

· T - open conductive parts are grounded, regardless of the nature of the connection between the power source and the ground;

· N - direct connection of open conductive parts of the electrical installation with the solidly grounded netal of the power source.

The letters following N through a dash determine the nature of this connection - the functional method of constructing the zero protective and zero working conductors:

· S - the functions of zero protective PE and zero working N conductors are provided by separate conductors;

· C - the functions of the neutral protective and neutral working conductors are provided by one common conductor PEN.

Protective function of earthing

Principle of protective action

The protective effect of grounding is based on two principles:

· Reducing the potential difference between a grounded conductive object and other naturally grounded conductive objects to a safe value.

· Discharge of leakage current when a grounded conductive object comes into contact with a phase wire. In a properly designed system, the occurrence of leakage current results in immediate tripping. protective devices(residual current devices - RCDs).

Thus, grounding is most effective only in combination with the use of residual current devices. In this case, with most insulation failures, the potential is grounded objects will not exceed dangerous values. Moreover, the faulty section of the network will be disconnected within a very short time (tenths ÷ hundredths of a second - the response time of the RCD).

Types of grounding systems

The classification of types of grounding systems is given as the main characteristics of the supply electrical network. GOST R 50571.2-94 “Electrical installations of buildings. Part 3. Basic characteristics" regulates following systems grounding: TN-C, TN-S, TN-C-S, TT, IT. TN-C system

The TN-C system (French Terre-Neutre-Combine) was proposed by the German concern AEG in 1913. The working neutral and the PE conductor (Protection Earth) in this system are combined into one wire. The biggest drawback was the possibility of phase voltage appearing on the housings of electrical installations in the event of an emergency zero break. Despite this, this system still found in buildings in the countries of the former USSR.

TN-S system

Separating zeros in TN-S and TN-C-S

To replace conditionally dangerous TN-C systems in the 1930s, the TN-S system (French Terre-Neutre-Separe) was developed, in which the working and protective zeros were separated directly at the substation, and the ground electrode was a rather complex structure of metal fittings. Thus, when the working zero was broken in the middle of the line, the electrical installation housings did not receive line voltage. Later, such a grounding system made it possible to develop differential circuit breakers and current leakage circuit breakers capable of sensing small currents. Their work to this day is based on Kirchhoff’s laws, according to which the current phase wire the current must be numerically equal to the current at the operating zero current.

You can also observe the TN-C-S system, where the separation of zeros occurs in the middle of the line, however, if the neutral wire breaks before the separation point, the housings will be under line voltage, which will pose a threat to life if touched.

System TN-C-S

In the TN-C-S system transformer substation has a direct connection of live parts with the ground. All exposed conductive parts of the building's electrical installation are directly connected to the grounding point of the transformer substation. To ensure this connection, a combined neutral protective and working conductor (PEN) is used in the section between the transformer substation and the electrical installations of the building. electrical circuit- separate neutral protective conductor (PE).

TT system

In the TT system, the transformer substation has a direct connection of live parts to the ground. All open conductive parts of the building's electrical installation have a direct connection to the ground through a ground electrode, electrically independent from the neutral ground electrode of the transformer substation.

IT system

In an IT system, the neutral of the power supply is isolated from earth or earthed through high resistance instruments or devices, and the exposed conductive parts are earthed. The leakage current to the frame or to ground in such a system will be low and will not affect the operating conditions of the connected equipment. The IT system is usually used in electrical installations of buildings and structures special purpose, which are subject to increased reliability and safety requirements, for example in hospitals for emergency power supply and lighting.

Grounding is a deliberate electrical connection of open conductive parts of electrical installations that are not in in good condition under voltage, with a solidly grounded neutral point of the generator or transformer, in three-phase current networks; with a solidly grounded output of a single-phase current source; with a grounded source point in DC networks, performed for electrical safety purposes. Protective grounding is the main measure of protection against indirect contact in electrical installations up to 1 kV with a solidly grounded neutral.

Operating principle

Operating principle of zeroing

The principle of operation of zeroing: if the voltage (phase) falls on the one connected to zero metal case device, a short circuit occurs. Circuit breaker, included in a damaged circuit, is triggered by a short circuit and disconnects the line from electricity. In addition, a fuse can disconnect electricity from the line. In any case, the PUE regulates the time automatic shutdown damaged line. For the rated phase voltage of the network 380/220 V, it should not exceed 0.4 s.