Protective grounding is a deliberate electrical connection to the ground or its equivalent of metal non-current-carrying parts that may become energized due to a short circuit to the case and for other reasons (inductive effect of neighboring current-carrying parts, potential removal, lightning discharge, etc.).

Protective grounding is designed to eliminate the risk of electric shock in case of contact with the body of the electrical installation and other non-current-carrying metal parts that are energized due to a short to the body and for other reasons.

The scope of protective grounding is electrical installations with voltage up to 1000 V in networks with an isolated central and above 1000 V in networks with any neutral mode of the current source (both isolated and dead-earthed).

In accordance with the requirements of GOST 12.1.030-81, protective grounding of an electrical installation should be performed:

at rated voltage of 380V and above AC and 440V and above DC in all cases;

at rated voltages from 42V to 380V AC and from 110V to 440V DC when working in conditions with increased danger, especially dangerous and outdoor installations.

Note: The characteristics of these conditions are given in the mandatory annex to GOST 12.1.013-78.

Protective grounding is applied to metal parts of electrical installations and equipment that are accessible to human touch and do not have other types of protection, for example, cases of electrical machines, transformers, lamps, switchboard frames, metal pipes and electrical wiring shells, etc.

The principle of operation of protective grounding in electrical installations with voltage up to 1000V:

decrease in the touch voltage on the grounded case when the supply voltage is shorted to it.

This is achieved due to the low resistance of the grounding device (Ohm). Current flows along the path of least resistance, and since human resistance (
kOhm), then it will go to the ground electrode or its equivalent.

Schematic diagram of protective grounding is shown in Fig.:

(a) - three-phase network; (b) - two-wire networks of alternating current and (c) - direct current.

Note: the maximum allowable values ​​of touch voltages and currents through the human body, taking into account the duration of exposure, are given in GOST 12.1.038-82.

Grounding is carried out using special devices - grounding conductors- this is a set of grounding conductors - metal conductors in contact with the ground, and grounding conductors connecting the grounded parts of the electrical installation with the grounding conductor.

Depending on the relative position of the grounding conductors and the equipment to be grounded, remote and loop grounding devices are distinguished. The first of them are characterized by the fact that the ground electrodes are placed outside the site on which the grounded equipment is located, or are concentrated on some part of this site (Fig. 20.4).

Loop grounding device (Fig. 20.5), the ground electrodes of which are located along the contour (perimeter) around the grounded equipment at a small distance from each other (several meters), provides a better degree of protection than the previous one

Grounding conductors are single and group, artificial and natural.

Group grounding consists of vertical rods and a horizontal strip connecting them.

As natural grounding conductors use:

Water pipe laid in the ground;

Well casing pipes (metal);

Lead sheaths of cables laid in the ground;

Other metal structures located in the ground.

The total resistance of the grounding device consists of the resistance of natural and artificial grounding conductors:

where
- the required (permissible) value of the resistance of the grounding device.

Requirements for protective grounding resistance are regulated by the PUE. At any time of the year, this resistance should not exceed 4 ohms

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Every day at home and at work, we have to deal with electricity, which makes human life more comfortable. But, despite the benefits that the use of electricity gives us, it still poses a certain danger, for example, electric shock. To avoid this, electrical safety requirements have been developed and special protection measures are taken. Such measures include zeroing and grounding. What is the difference between them and is there any, we will understand in this article.

All electrical work must only be carried out by qualified personnel.

The main requirement for household electrical appliances is safety. To a greater extent, this applies to devices that come into contact with water, because even a minor defect in the equipment can be fatal to the user. To protect yourself and those around you, you must keep the power grid and equipment in good condition and regularly revise them.To eliminate the possibility of a fire due to faulty wiring and electric shock, it is necessary to install protective devices (RCD).

In accordance with the basic rules of electrical safety:

This is only a short list of electrical safety requirements. More detailed information about safety rules can be found in various regulations and special literature on electricity, which are now easily found on the Internet.

What is grounding, principle of operation and device

When creating an electrical network in premises for various purposes, it is necessary to create protection that will prevent possible electric shock. To avoid this, a grounding device is provided. In accordance with PES clause 1.7.53, grounding is carried out in electrical equipment with a voltage of more than 50 V AC and 120 V DC.

Grounding - the intentional connection of non-current-carrying metal parts of electrical installations (which may be energized) to the ground or its equivalent. This protective measure is designed to eliminate the possibility of electric shock to a person in the event of a short circuit to the equipment case.

Operating principle

The principle of operation of protective grounding is:

• reducing the potential difference between the grounded element and other conductive objects with natural grounding, to a safe value;
• current removal in case of direct contact of the grounded equipment with a phase conductor. In a well-designed electrical network, the occurrence of a leakage current causes an instantaneous operation of the residual current device (RCD).

From the foregoing, it follows that grounding is more effective when used in combination with an RCD.

Grounding device

The design of the grounding system consists of a ground electrode (a conductive part that has direct contact with the ground) and a conductor that provides contact between the ground electrode and non-current-carrying elements of electrical equipment. Usually, a steel or copper (very rarely) rod is used as a ground electrode; in industry, this is usually a complex system consisting of several elements of a special shape.

The effectiveness of the grounding system is largely determined by the resistance value of the protective device, which can be reduced by increasing the useful area of ​​the ground electrodes or by increasing the conductivity of the medium, for which several rods are used, the level of salts in the ground increases, etc.

The grounding device is...

Above, we examined in general terms what protective grounding is. However, it is worth mentioning that the earth electrodes used in the system differ in natural and artificial.

As grounding devices, it is primarily preferable to use such natural grounding conductors as:

Important! It is forbidden to use pipelines with gas and flammable liquids, as well as heating mains as a grounding element.

Natural grounding conductors must be connected to the protective system from two or more different points.

As an artificial grounding can be used:

• steel pipe with a wall thickness of 3.5 mm and a diameter of 30 ÷ 50 mm and a length of about 2 ÷ 3 m;
• steel strips and corners with a thickness of 4 mm;
• steel bars with a length of up to 10 meters or more and a diameter of 10 mm.

For aggressive soils, it is necessary to use artificial ground electrodes with high resistance to corrosion and made of copper, galvanized or copper-plated metal.So, we figured out what is the definition of the concept of artificial and natural grounding, now let's look at when grounding is applied.

The proposed video clearly explains what protective grounding is:

When and where is grounding applied?

As already mentioned, protective grounding is intended to eliminate the possibility of electric shock to people in the event that voltage is applied to the conductive parts of the equipment, that is, when there is a short to the case.Protective grounding is equipped with metal non-current-carrying elements of electrical installations, which, due to a possible breakdown of wire insulation, may become energized and harm the health and life of people and animals in case of direct contact with faulty equipment.

Electrical networks and equipment with voltage up to 1000 V are subject to grounding, namely:

• alternating current;
• three-phase with isolated neutral;
• two-phase, isolated from the earth;
• direct current;
• current sources with an isolated winding point.

Also, grounding is necessary for electrical networks and electrical installations of direct and alternating current with a voltage of more than 1000 V with any neutral or midpoint of the current source winding.

The main methods of grounding device

When constructing a grounding system, vertical metal rods are usually used as a ground electrode. This is due to the fact that horizontal electrodes, due to the shallow depth of occurrence, have an increased electrical resistance. As vertical electrodes, steel pipes, rods, angles and other rolled metal products with a length exceeding 1 meter and having a relatively small cross section are almost always used.

There are two main methods for mounting vertical ground electrodes.

Related article:

Electricity can not only create comfortable living conditions, but also carries a certain danger. To reduce the likelihood of this hazard, do-it-yourself grounding in a private house 220V. How to do it - read in the publication.

Several short electrodes

In this option, several steel angles or rods 2-3 meters long are used, which are connected together using a metal strip and welding. The connection is made near the surface of the earth.The installation of the earth electrode is carried out by simply driving the electrode into the ground using a sledgehammer. A similar method is better known as the "corner and sledgehammer."

The minimum permitted cross section of the grounding electrodes is given in the PUE, but most often the corrected and supplemented values ​​are from the technical circular No. 11 of RusElectroMontazh. In particular:

The advantages of this method are simplicity, low cost and availability of materials and installation.

Single electrode

In this case, an electrode in the form of a steel pipe (usually single) is used as a ground electrode, which is placed in a deep hole drilled in the ground. Drilling the soil and installing the electrode requires the use of special equipment.

An increase in the area of ​​contact of the ground electrode with the ground is provided by a greater depth of installation of the electrode. Moreover, this method is more efficient in comparison with the previous version, with the same total length of the electrodes, due to the achievement of deep soil layers, which usually have a low electrical resistivity.

The advantages of this method include high efficiency, compactness and seasonal "independence", i.e. due to the winter freezing of the soil, the specific resistance of the earth electrode practically does not change.

Another way is to lay a ground electrode in a trench. However, this option requires large physical and material costs (more material, trench digging, etc.).

Having figured out how it works and why grounding is needed, now the second question of our article is, namely, what is zeroing, what is it for and how is it different from grounding.

What is nulling

The term grounding refers to the deliberate connection of open, non-current-carrying conductive parts of the electrical network and equipment with a solidly grounded point in single- and three-phase DC and AC networks. Zeroing is carried out for electrical safety purposes and is the main protective tool against getting under voltage.

Operating principle

A short circuit in the mains occurs when a phase wire under voltage comes into contact with the body of the device, connected to zero. The current strength increases sharply, and protective devices are activated that cut off power from faulty equipment. According to the rules, the RCD response time to turn off a faulty electrical network should not exceed 0.4 seconds. This requires that the phase and zero have a small amount of resistance.

Related article:

Have you ever heard an abbreviation, you will know by reading the review to the end. In short, I would like to add that this device is able to protect housing and all its inhabitants from emergencies associated with electricity.

To create a zero in a single-phase network, as a rule, use the third (unused) wire of a three-core cable. To create good protection, it is necessary to ensure a high-quality connection of all elements of the zeroing system.

Device

The grounding system, for example, in an apartment building, begins with a grounded power transformer, from which the neutral with a three-phase line comes to the main switchboard (MSB) of the building. Next happens. A working zero is created from the neutral, which together with the phase wire form the usual single-phase voltage.

Zeroing itself for the protection of the electrical network and equipment is created in the shield using a conductor connected to a grounded neutral. You should be aware that it is forbidden to install switching devices between zero and neutral (automatic machines, packet switches, knife switches, etc.).

Where is the grounding scheme applied?

According to the requirements of the PES, protective earthing must be equipped with:

• single- and three-phase alternating current networks with a grounded output and voltage up to 1,000 V;
• DC electrical networks with an average grounding point and voltage up to 1,000 V.

Grounding cannot protect against electric shock like grounding. This protection circuit simply cuts off the power supply in the event of a short circuit and cuts off the local power grid.

Is it possible to do grounding in an apartment using grounding

We already know what grounding and grounding are and we will try to find out if grounding can be done using a grounded zero located in the electrical panel. The fact is that many people far from electrical engineering ask this question and often make unforgivable mistakes by doing just that.

First, it is prohibited by the PES. The fact is that if, for example, during installation work, for some reason, the phase and zero are mixed up in places, and besides, zeroing is brought to a working zero, then the most unpleasant situations can be expected. When electrical equipment is connected to the network, the case will be energized and a person will be struck by electric current, since the protective operation of the RCD will not occur.

To create a protective grounding in the storey electrical panel, a separate bus is allocated, which is connected to a solidly grounded neutral. And it is best not to perform these works on your own, but to entrust a specialist with knowledge in electrical engineering.

The video shows how to create a zero if it is not in the storey electrical panel:

What is the difference between grounding and grounding

It should be said right away that despite the fact that grounding and zeroing are protective measures, they have differences in the principle of operation and purpose.Grounding is a more effective and reliable method of protection than zeroing, since it allows you to quickly equalize the difference between the potentials to the required value. Also, grounding has a simpler design and is easier to install, and for its installation you just need to follow the instructions. In addition, this protective circuit does not depend on the phase of the connected equipment. Grounding options are varied, and this allows you to choose a specific type for each specific case.

Protective neutralization is a protective measure that, in the event of a network failure, simply ensures that the supply of voltage from the mains is instantly interrupted by tripping the RCD. To create a zero and connect equipment requires experience and certain knowledge in electrical engineering. All installation work, especially the determination of the neutral point, must be carried out correctly, otherwise an electric shock may result in an emergency.

Having figured out what grounding and grounding are, many prefer to use both methods. However, grounding is mandatory for the installation of household and industrial networks, as well as the operation of equipment.

To better understand the difference between grounding and grounding, we suggest watching this video:

Requirements for grounding and grounding

Grounding is a more serious protective measure than grounding. This scheme requires the creation of a separate low-resistance bus, which is connected to a grounding conductor dug into the ground and equipped in accordance with the standards. All requirements for grounding, its elements and arrangement are prescribed in the PES and GOST 12.2.007.0.

In the industrial sector, grounding is subject to:

• electric drives;
• electrical equipment cases;
• metal structures of buildings;
• shielded braid of low-voltage electrical cables;
• enclosures of electrical distribution boards and similar structures.

There are more loyal requirements for zeroing, namely:

• neutral and phase conductors are selected in such a way that during a breakdown on the equipment case, a current sufficient to trigger an RCD or other protective mechanism occurs;
• the grounding conductor from the device to the grounded neutral must be continuous, that is, it must not contain any switching devices in the circuit.

Summing up

Ensuring the safety of life and health is the primary task of the state, society and, of course, the individual himself. To do this, you must strictly adhere to the established rules, instructions and requirements. One of the factors hazardous to human health is electricity, so it is very important to ensure sufficient electrical safety at work and at home with the help of certain measures and protective equipment.

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Protective earthing is the intentional connection to earth of metal parts of equipment that are not normally energized, but which may become energized as a result of a failure in the insulation of an electrical installation.

The purpose of protective grounding is to eliminate the danger of electric shock to people when voltage appears on the structural parts of electrical equipment, i.e., when a “short circuit to the case” occurs.

The principle of operation of protective grounding is to reduce the contact and step voltages to safe values, due to a "short circuit to the case". This is achieved by reducing the potential of grounded equipment, as well as by equalizing potentials by raising the potential of the base on which a person stands to a potential close in magnitude to the potential of grounded equipment.

The scope of protective grounding is three-phase three-wire networks with voltage up to 1000 V with an isolated neutral and above 1000 V with any neutral mode (Fig. 71).

Rice. 71. Schematic diagrams of protective grounding:
a - in a network with an isolated neutral up to 1000 V and above; b - in a network with a grounded neutral above 1000 V, 1 - grounded equipment; 2 - protective earthing; 3 - ground electrode for working grounding; r3. ro are the resistances of the protective and working grounds, respectively

Types of grounding devices. A grounding device is a set of grounding conductors - metal conductors that are in direct contact with the ground, and grounding conductors connecting the grounded parts of the electrical installation with the grounding conductor. There are two types of grounding devices: remote (or concentrated) and contour (or distributed).

An external grounding device is characterized by the fact that its ground electrode is placed outside the site on which the grounded equipment is located, or is concentrated on some part of this site.

The disadvantage of remote grounding is the remoteness of the ground electrode from the protected equipment, as a result of which the touch coefficient a \u003d 1. Therefore, this type of grounding is used only at low earth fault currents and, in particular, in installations with voltages up to 1000 V, where the potential of the earth electrode does not exceed the allowable contact voltage .

The advantage of this type of grounding device is the ability to choose the location of the electrodes with the lowest soil resistance (damp, clay, in lowlands, etc.).

The contour grounding device is characterized by the fact that its single grounding conductors are placed along the contour (perimeter) of the site on which the grounded equipment is located, or distributed throughout the site as evenly as possible.

Safety with loop grounding is ensured by equalizing the potential in the protected area to such a value that the maximum values ​​​​of the touch and step voltages do not exceed the permissible values. This is achieved by appropriate placement of single earthing switches.

Indoors, potential equalization occurs naturally through metal structures, pipelines, cables and similar conductive objects connected to an extensive ground network.

Implementation of grounding devices. There are artificial grounding conductors, intended exclusively for grounding purposes, and natural ones - metal objects located in the ground for other purposes.

For artificial ground electrodes, vertical and horizontal electrodes are usually used.

As vertical electrodes, steel pipes with a diameter of 3–5 cm and angle steel measuring from 40 X 40 to 60 X 60 mm and 2.5–3 m long are used. In recent years, steel bars with a diameter of 10–12 mm and a length of up to 10 m have been used. .

To connect vertical electrodes and as an independent horizontal electrode, use strip steel with a cross section of at least 4 X 12 mm or round steel with a diameter of at least 6 mm.

To install vertical grounding devices, they first dig a trench with a depth of 0.7-0.8 m, after which pipes or corners are clogged with the help of mechanisms.

The following can be used as natural grounding conductors: water and other metal pipelines laid in the ground, with the exception of pipelines of flammable liquids, flammable or explosive gases, as well as pipelines covered with insulation to protect against corrosion; casing pipes of artesian wells, wells, pits, etc.; metal structures and reinforcement of reinforced concrete structures of buildings and structures that are connected to the ground; lead sheaths of cables laid in the ground. Natural grounding conductors, as a rule, have a low resistance to current spreading, and therefore their use for grounding purposes provides very tangible savings. The disadvantages of natural ground electrodes are their accessibility to non-electrotechnical personnel and the possibility of breaking the continuity of the connection of extended ground electrodes (during repair work, etc.).

As grounding conductors intended for connecting grounding parts with grounding conductors, as a rule, strip steel, as well as round steel, etc. are used. Grounding conductors are laid openly along building structures, including along walls on special supports. Grounding conductors in the premises must be accessible for inspection.

Grounded equipment is connected to the grounding line using separate conductors. In this case, the series connection of grounded equipment is not allowed.

According to the requirements of the Electrical Installation Rules, the protective grounding resistance at any time of the year should not exceed:

4 Ohm - in installations with voltage up to 1000 V; if the power of the current source (generator or transformer) is less than 100 kVA, then the grounding resistance is allowed 10 ohms;

0.5 Ohm - in installations with voltages above 1000 V with high ground fault currents (more than 500 A);

250/I3, but not more than 10 Ohm - in installations with voltages above 1000 V with low earth fault currents and without compensation of capacitive currents; if the grounding device is simultaneously used for electrical installations up to 1000 V, then the grounding resistance should not exceed 125 / I3, but not more than 10 ohms (or 4 ohms, if required for installations up to 1000 V). Here I3 is the earth fault current.

Equipment to be grounded. Protective grounding is subject to metal non-current-carrying parts of electrical equipment, which, due to insulation failure, may become energized, and which can be touched by people and animals. At the same time, in rooms with increased danger or especially dangerous, grounding is mandatory at a rated voltage of the electrical installation above 36 V AC and 110 V DC, and in rooms without increased danger - at a voltage of 500 V and above. Only in hazardous areas, grounding is carried out regardless of the magnitude of the voltage.

grounding

Form start

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A warning: the article is purely informative and is not a normative document. When performing work related to electricity, you should be guided by the Electrical Installation Rules (PUE).

Definitions

grounding- this is a deliberate connection of non-current-carrying equipment elements, which, as a result of insulation breakdown, may become energized, with the ground. Grounding consists of a grounding conductor (a conductive part or a set of interconnected conductive parts that are in electrical contact with the ground directly or through an intermediate conductive medium) and a grounding conductor connecting the grounded device to the grounding conductor. The grounding conductor can be a simple metal rod (most often steel, less often copper) or a complex set of special-shaped elements. The quality of grounding is determined by the value of the electrical resistance of the grounding circuit, which can be reduced by increasing the contact area or the conductivity of the medium - using many rods, increasing the salt content in the ground, etc. As a rule, the electrical resistance of grounding is normalized. Main ground clamp. To minimize electromagnetic interference and maintain electrical safety, grounding should be performed with a minimum number of closed loops. Ensuring this condition is possible when performing the so-called main ground clamp (GZZ), or bus. The main earth clamp should be located as close as possible to the input power and communication cables and connected to the earth electrode(s) with the shortest conductor length. This location of the GZZ provides the best potential equalization and limits the induced voltage from industrial interference, lightning and switching overvoltages coming from the outside through the screens of communication cables, armor of power cables, pipelines and antenna bushings. To GZZ (tire) must be attached:

grounding conductors;

protective conductors;

conductors of the main potential equalization system;

working ground conductors (if necessary).

Protective and working (technological, logical, etc.) grounding conductors, lightning protection grounding conductors, etc. must be connected to the main grounding terminal (bus). exposed conductive part- a conductive part of an electrical installation accessible to touch that is not normally energized, but which may become energized if the basic insulation is damaged. Open conductive parts include metal cases of electrical equipment. live part- the electrically conductive part of the electrical installation, which is under operating voltage during its operation. indirect touch- electrical contact of people and animals with open conductive parts that are energized when the insulation is damaged. That is, this is a touch on the metal case of electrical equipment during the breakdown of insulation on the case.

Notation

Protective grounding conductors in all electrical installations, as well as zero protective conductors in electrical installations with voltage up to 1 kV with a solidly grounded neutral, including tires, must have a letter designation RE and color designation by 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 indicated by the letter N and blue. Combined zero protective and zero working conductors must have a letter designation PEN and color designation: blue color along the entire length and yellow-green stripes at the ends. Graphic symbols used to designate conductors in diagrams:

Grounding designation:

Letter designations of the grounding system

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 supply to the ground; I– all current-carrying parts are isolated from the ground. The second letter determines the nature of the grounding of the open conductive parts of the electrical installation of the building: T- direct connection of the open conductive parts of the electrical installation of the building with the ground, 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 of the building with the grounding point of the power source. The letters following through the dash behind N determine the nature of this connection - a functional way of arranging the zero protective and zero working conductors: S– functions of zero protective PE and zero working N conductors are provided by separate conductors; C- the functions of the zero protective and zero working conductors are provided by one common PEN conductor.

Errors in the grounding device

Wrong PE conductors Sometimes water pipes or heating pipes are used as a ground conductor, but they cannot be used as a ground conductor. There may be non-conductive inserts in the plumbing (such as plastic pipes), the electrical contact between the pipes may be broken due to corrosion, and finally, a part of the pipeline may be dismantled for repair.

Combining a working zero and a PE conductor Another common violation is the union of the working zero and the PE conductor beyond the point of their separation (if any) along the distribution of energy. Such a violation can lead to the appearance of quite significant currents in the PE conductor (which should not be current-carrying in the normal state), as well as to false trips of the residual current device (if installed).

Incorrect separation of the PEN conductor The following way of “creating” a PE conductor is extremely dangerous: a working neutral conductor is determined directly in the socket and a jumper is placed between it and the PE contact of the socket. Thus, the PE conductor of the load connected to this outlet is connected to the working zero. The danger of this circuit is that a phase potential will appear on the grounding contact of the socket, and, consequently, on the case of the connected device, if any of the following conditions are met:

Rupture (disconnection, burnout, etc.) of the neutral conductor in the area between the socket and the shield (and further, up to the grounding point of the PEN conductor);

Swapping the phase and zero (phase instead of zero and vice versa) conductors going to this outlet.

grounding

This article is about the grounding of electrical installations necessary to ensure electrical safety - protecting a person from electric shock. For the term in radio communications, see Counterweight (radio engineering).; for the "ground" wire in electronics, see Ground (electronics).

1.7.28. grounding- intentional electrical connection of any point of the network, electrical installation or equipment with a grounding device.

Chapter 1.7 GROUNDING AND ELECTRICAL SAFETY. Application area. Terms and Definitions
Rules for the installation of electrical installations (PUE) Seventh edition. Approved by the Order of the Ministry of Energy of Russia dated 08.07.2002 No. 204

In electrical engineering, with the help of grounding, the contact voltage is reduced to a value that is safe for humans and animals.

Terminology

• Solidly grounded neutral- transformer or generator neutral connected directly to the earthing device. The output of a single-phase AC source or the pole of a DC source in two-wire networks, as well as the midpoint in three-wire DC networks, can also be dead-earthed.
• Isolated neutral- the neutral of a transformer or generator, not connected to a grounding device or connected to it through a large resistance of signaling, measuring, protection devices and other similar devices.

• Grounding device- a set of grounding conductors and grounding conductors.
• grounding conductor- a conductive part or a set of interconnected conductive parts that are in electrical contact with the ground directly or through an intermediate conductive medium.
  • Artificial grounding- a grounding conductor specially made for grounding purposes.
  • Natural grounding- a third-party conductive part in electrical contact with earth, directly or through an intermediate conductive medium, used for earthing purposes.
• Ground conductor- a conductor connecting the grounded part (point) with the ground electrode.
• Protective (PE) conductor- a conductor intended for electrical safety purposes.
• Protective earth conductor- protective conductor intended for protective earthing.
• Protective potential equalization conductor- protective conductor intended for protective equalization of potentials.
• Zero protective conductor- a protective conductor in electrical installations up to 1 kV, designed to connect open conductive parts to a solidly grounded neutral of a power source.
• Zero working (neutral) conductor (N)- a conductor in electrical installations up to 1 kV, designed to power electrical receivers and connected to a solidly grounded neutral of a generator or transformer in three-phase current networks, with a solidly grounded output of a single-phase current source, with a solidly grounded source point in DC networks.
• Combined zero protective and zero working (PEN) conductors- conductors in electrical installations with voltage up to 1 kV, combining the functions of zero protective and zero working conductors.
• Main ground bus- a busbar that is part of the grounding device of an electrical installation up to 1 kV and is designed to connect several conductors for the purpose of grounding and potential equalization.
• Conductive part- a part that can conduct electricity.
• live part- the conductive part of the electrical installation, which is under operating voltage during its operation, including the zero working conductor (but not the PEN conductor).
• exposed conductive part- accessible to touch conductive part of the electrical installation, normally not energized, but which may become energized if the basic insulation is damaged.
• Third party conductive part- a conductive part that is not part of the electrical installation.
• Zero potential zone (relative earth)- a part of the earth that is outside the zone of influence of any grounding conductor, the electric potential of which is assumed to be zero.

• Protective earth- grounding performed for electrical safety purposes.
• Working (functional) grounding- grounding of a point or points of current-carrying parts of an electrical installation, performed to ensure the operation of an electrical installation (not for electrical safety purposes).
• Protective grounding in electrical installations with voltage up to 1 kV- intentional connection of open conductive parts with a solidly grounded neutral of a 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.
• Potential equalization- electrical connection of conductive parts to achieve equality of their potentials.
• Protective potential equalization- equalization of potentials, performed for the purpose of electrical safety.
• Potential equalization- reduction of the potential difference (step voltage) on the surface of the ground or floor with the help of protective conductors laid in the ground, in the floor or on their surface and connected to a grounding device, or by using special ground coverings.
• Spreading zone (local ground) - the zone of the earth between the ground electrode and the zone of zero potential.
• ground fault- accidental electrical contact between energized live parts and earth.

• direct touch- electrical contact of people or animals with live parts under voltage.
• indirect touch- electrical contact of people or animals with open conductive parts that are energized when the insulation is damaged.

• Protection against direct contact- protection to prevent contact with live parts under voltage.
• Protection against indirect contact- protection against electric shock when touching open conductive parts that are energized when the insulation is damaged.
• Protective automatic power off- automatic opening of the circuit of one or more phase conductors (and, if required, the neutral working conductor), performed for electrical safety purposes.
• Isolating transformer- a transformer, the primary winding of which is separated from the secondary windings by means of protective electrical separation of circuits.
• Safety isolating transformer- isolating transformer designed to power circuits with extra-low voltage.
• protective screen- a conductive screen designed to separate an electrical circuit and / or conductors from the current-carrying parts of other circuits.

• Protective electrical separation of circuits- separation of one electrical circuit from other circuits in electrical installations with voltage up to 1 kV using:
  • double insulation;
  • basic insulation and protective screen;
  • reinforced insulation.

• Basic insulation- insulation of current-carrying parts, providing, among other things, protection against direct contact.
• Additional insulation- independent insulation in electrical installations with voltage up to 1 kV, performed in addition to the main insulation for protection in case of indirect contact.
• double insulation- insulation in electrical installations with voltage up to 1 kV, consisting of basic and additional insulation.
• Reinforced insulation- insulation in electrical installations with voltage up to 1 kV, providing a degree of protection against electric shock equivalent to double insulation.
• Non-conductive (insulating) rooms, zones, sites- premises, zones, platforms in which (on which) protection in case of indirect contact is provided by high resistance of the floor and walls and in which there are no grounded conductive parts.

• Earth fault ratio in a three-phase electrical network- the ratio of the potential difference between the undamaged phase and earth at the point of earth fault of another or two other phases to the potential difference between the phase and earth at this point before the fault.

• Grounding device voltage- voltage that occurs when current drains from the ground electrode into the ground between the point of current input into the ground electrode and the zone of zero potential.
• Touch voltage- the voltage between two conductive parts or between a conductive part and earth when a person or animal touches them at the same time.
• Expected touch voltage- the voltage between simultaneously accessible conductive parts when a person or animal does not touch them.
• Step Voltage- the voltage between two points on the surface of the earth, at a distance of 1 m from one another, which is taken equal to the length of a person's step.
• Extra low (low) voltage (SLV)- voltage not exceeding 50 V AC and 120 V DC.

• Grounding device resistance- the ratio of the voltage on the grounding device to the current flowing from the grounding conductor into the ground.
• Equivalent earth resistivity with non-homogeneous structure- electrical resistivity of the earth with a homogeneous structure, in which the resistance of the grounding device has the same value as in the earth with a heterogeneous structure.

Term "Earth", used in the chapter, should be understood as the ground in the spreading zone.

Term "resistivity", used in the chapter for earth with a non-uniform structure, should be understood as equivalent resistivity.

Term "insulation failure" should be understood as the only insulation failure.

Term "automatic power off" should be understood as protective automatic power off.

Term "potential equalization" used in the chapter should be understood as protective potential equalization.

Notation

Grounding device

In Russia, the requirements for grounding and its device are regulated by the Electrical Installation Rules (PUE). Grounding in electrical engineering is divided into natural and artificial.

Natural ground

Earthing switch (metal rod) with connected earth conductor

It is customary to refer to natural grounding those structures, the structure of which provides for a permanent stay in the ground. However, since their resistance is not regulated by anything and there are no requirements for the value of their resistance, natural grounding structures cannot be used as the grounding of an electrical installation. Natural grounding conductors include, for example, pipes.

Artificial ground

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

Grounding device(GD) consists of a grounding conductor (a conductive part or a set of interconnected conductive parts that are in electrical contact with the ground directly or through an intermediate conductive medium) and a grounding conductorconnecting the grounded part (point) to the grounding conductor. The grounding conductor can be a simple metal rod (most often steel, less often copper) or a complex set of special-shaped elements.

The quality of grounding is determined by the value of grounding resistance / current spreading resistance (the lower, the better), which can be reduced by increasing the area of ​​grounding electrodes and reducing the electrical resistivity of the soil: increasing the number of grounding electrodes and / or their depth; increasing the concentration of salts in the soil, heating it, etc.

The electrical resistance of the grounding device is different for different conditions and is determined / standardized by the requirements of the PUE and relevant standards.

Varieties of artificial grounding systems

Some types of grounding systems for electrical networks. TN-S came in the 1930s to replace TN-C after a large number of electrical injuries when the neutral wire was broken, since the cross section of the neutral wire was usually taken 1/3 of the thickness of the cross section of the phase wires

Electrical installations in relation to electrical safety measures are divided into:

• electrical installations with voltages above 1 kV in networks with dead-earthed or effectively grounded neutral;
• electrical installations with voltages above 1 kV in networks with isolated or grounded neutral through an arcing reactor or resistor;
• electrical installations with voltage up to 1 kV in networks with dead-earthed neutral;
• electrical installations with voltage up to 1 kV in networks with isolated neutral.

Depending on the technical features of the electrical installation and the supply networks, its operation may require different grounding systems. As a rule, before designing an electrical installation, the sales organization issues a list of specifications that specifies the earthing system used.

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

For electrical installations with voltage up to 1 kV, the following designations are accepted:

• system TN - a system in which the neutral of the power source is solidly grounded, and the open conductive parts of the electrical installation are connected to the solidly grounded neutral of the source by means of zero protective conductors;
• system TN-C - system TN, in which the zero protective and zero working conductors are combined in one conductor along its entire length;
• system TN-S - system TN, in which the zero protective and zero working conductors are separated along its entire length;
• system TN-C-S - system TN, in which the functions of the zero protective and zero working conductors are combined in one conductor in some part of it, starting from the power source;
• system IT - a system in which the neutral of the power supply is isolated from earth or earthed through devices or devices with high resistance, and the exposed conductive parts of the electrical installation are earthed;
• system TT - a system in which the neutral of the power source is solidly grounded, and the open conductive parts of the electrical installation are grounded using a grounding device that is electrically independent of the solidly grounded neutral of the source.

• T - grounded neutral (lat. terra);
• I - isolated neutral isolation).

• 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.

• S - zero worker ( N) and zero protective ( RE) conductors are separated (eng. separated);
• With - the functions of the zero protective and zero working conductors are combined in one conductor (PEN-conductor) (eng. combined);
• N - zero working (neutral) conductor; (English) neutral)
• RE - protective conductor (grounding conductor, zero protective conductor, protective conductor of the potential equalization system) (eng. Protective Earth)
• PEN - combined zero protective and zero working conductors (eng. Protective Earth and Neutral).

Systems with solidly earthed neutral ( TN-systems)

Systems with a solidly grounded neutral are commonly called TN-systems, since this abbreviation comes from fr. Terre Neutral, which means "ground-neutral".

System TN-C

System TN-C (fr. Terre-Neutre-Combine) was proposed by the German concern AEG in 1913. Working zero and PE- conductor Protection Earth) in this system are combined into one wire. The biggest drawback was the possibility of the appearance of phase voltage on the housings of electrical installations during an emergency break zero. Despite this, this system is still found in the buildings of the countries of the former USSR. Of modern electrical installations, such a system is found only in street lighting for reasons of economy and reduced risk.

System TN-S

System TN-S (fr. Terre-Neutre-Separe) was developed to replace the conditionally dangerous system TN-C in the 1930s. The working and protective zero were separated directly at the substation, and the ground electrode was a rather complex design of metal fittings. Thus, when the working zero was interrupted in the middle of the line, the electrical installations did not receive line voltage. Later, such a grounding system made it possible to develop differential automata and current leakage automata, capable of sensing a small current. Their work to this day is based on Kirchhoff's laws, according to which the current flowing at the working zero must be numerically equal to the geometric sum of the currents in the phases.

• You can also see the system TN-C-S, where the separation of zeros occurs in the middle of the line, however, in the event of a break in the neutral wire before the separation point, the cases will be under line voltage, which will be life-threatening when touched.

System TN-C-S

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

• Advantages: a simpler lightning protection device (it is impossible for a voltage peak to appear between PE and N), the ability to protect against phase short circuits on the device case using ordinary "automatic machines".

• Disadvantages: extremely weak protection against "burning out zero", that is, destruction PEN on the way from the CTP to the separation point. In this case, the bus PE on the consumer side, a phase voltage appears, which cannot be turned off by any automation ( PE cannot be disabled). If inside the building the EMS serves as protection against this (everything metal is energized, and there is no risk of electric shock when touching 2 different objects), then in the open air there is no protection from this at all.

In accordance with the PUE, it is the main and recommended system, but at the same time, the PUE require compliance with a number of measures to prevent destruction PEN- mechanical protection PEN, as well as repeated grounding PEN overhead line along poles over a certain distance (no more than 200 meters for areas with up to 40 thunderstorm hours per year, 100 meters for areas with more than 40 thunderstorm hours per year).

In the event that these measures cannot be observed, the EMP recommend TT. Also TT recommended for all outdoor installations (sheds, porches, etc.)

Bus in city buildings PEN usually a thick metal frame running vertically through the entire building. It is almost impossible to destroy it, therefore, in urban buildings it is used TN-C-S.

In rural areas in Russia, in practice, there are a huge number of overhead lines without mechanical protection. PEN and re-groundings. Therefore, in rural areas, the system is more popular. TT.

In late Soviet urban development, as a rule, TN-C-S with a division point based on the electrical panel ( PEN) next to the counter, while PE carried out only for electric stoves.

In modern Russian development, “five-wire” is also used with a dividing point in the basement, independent N and PE.

System TT

In system TT the transformer substation has a direct connection of current-carrying parts with the ground. All open conductive parts of the electrical installation of the building have a direct connection to the ground through a grounding conductor, electrically independent of the neutral grounding conductor of a transformer substation.

• Advantages: high resistance to destruction N on the way from TP to the consumer. This destruction does not affect PE.

• Disadvantages: requirements for more complex lightning protection (the possibility of a peak appearing between N and PE), as well as the impossibility for a conventional circuit breaker to track the short circuit of the phase to the device case (and further to PE). This is due to the rather noticeable (30-40 ohm) local ground resistance.

In view of the above, the PUE recommend TT only as an "additional" system (provided that the supply line does not meet the requirements TN-C-S for re-grounding and mechanical protection PEN), as well as in outdoor installations where there is a risk of simultaneous contact with the installation and physical earth (or physically earthed metal parts).

However, due to the poor quality of most overhead lines in rural areas of Russia, the system TT extremely popular there.

TT requires mandatory use of RCD. Usually, an introductory RCD is installed with a setting of 300-100 mA, which monitors the short circuit between phase and PE, followed by personal RCDs for specific circuits at 30-10 mA to protect people from electric shock.

Lightning protection devices such as ABB OVR, differ in design for systems TN-C- S and TT, in the latter a gas discharger is installed between N and PE and varistors between N and phases.

Systems with isolated neutral

IT system

In system IT the neutral of the power supply is isolated from earth or earthed through instruments or devices with high resistance, and 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.

System IT It is used, as a rule, in electrical installations of buildings and structures for special purposes, which are subject to increased requirements for reliability and safety, for example, in hospitals for emergency power supply and lighting.

Protective function of grounding

The principle of protective action

The protective effect of grounding is based on two principles:

• Reduction to a safe value of the potential difference between a grounded conductive object and other conductive objects that have a natural ground.
• Removal of leakage current when a grounded conductive object contacts a phase conductor. In a properly designed system, the appearance of a leakage current leads to the immediate operation of protective devices (residual current devices - RCDs).
• In systems with a solidly grounded neutral - initiation of a fuse when a phase potential hits a grounded surface.

Thus, grounding is most effective only in combination with the use of residual current devices. In this case, with most insulation failures, the potential on 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 RCD trip time).

Grounding operation in case of electrical equipment malfunctions

A typical case of a malfunction of electrical equipment is the ingress of phase voltage on the metal case of the device due to insulation failure. (It should be noted that modern electrical appliances that have a pulse and are equipped with a three-pole plug, such as a PC system unit, in the absence of grounding, have a dangerous potential on the case, even when they are fully operational.) Depending on what protective measures are implemented, the following options are possible:

Options described

The case is not grounded, there is no RCD (the most dangerous option).

• The body of the device will be under phase potential and this will never be found. Touching such a malfunctioning device can be fatal.

• If the leakage current in the circuit phase-housing-grounding is large enough (exceeds the threshold of the fuse that protects this circuit), the fuse will trip and turn off the circuit. The highest operating voltage (relative to earth) on a grounded case will be U max =R G I F, where R G− ground electrode resistance, I F− the current at which the fuse protecting this circuit operates. This option is not safe enough, since with a high resistance of the ground electrode and large fuse ratings, the potential on the grounded conductor can reach quite significant values. For example, with a grounding resistance of 4 ohms and a 25 A fuse, the potential can reach 100 volts.

• The case of the device will be at phase potential and this will not be detected until there is a path for the leakage current to pass. In the worst case, leakage will occur through the body of a person who has touched both a faulty device and an object that has a natural ground. The RCD disconnects the section of the network with a malfunction as soon as a leak occurs. A person will receive only a short-term electric shock (0.01 ... 0.3 s - RCD operation time), which, as a rule, does not cause harm to health.

• This is the safest option since the two protective measures complement each other. When a phase voltage hits a grounded conductor, the current flows from the phase conductor through an insulation fault into the ground conductor and further into the ground. The RCD immediately detects this leak, even if it is very insignificant (usually the RCD sensitivity threshold is 10 mA or 30 mA), and quickly (0.01 ... 0.3 s) disconnects the section of the network with a malfunction. In addition, if the leakage current is high enough (greater than the threshold of the fuse protecting that circuit), then the fuse may also blow. Which protective device (RCD or fuse) will turn off the circuit depends on their speed and leakage current. It is also possible for both devices to operate.

Errors in the grounding device

Wrong PE- conductors

Sometimes water pipes or heating pipes are used as a ground conductor, but they cannot be used as a ground conductor. There may be non-conductive inserts in the plumbing (such as plastic pipes), the electrical contact between the pipes may be broken due to corrosion, and finally, a part of the pipeline may be dismantled for repair. There is also a danger of electric shock when in contact with conductive parts of plumbing.

"Pure Land"

A popular belief is that computer and telephone installations require an earth connection separate from the general building earth.

This is completely wrong, because the memory has a non-zero resistance, and, in the case of a short circuit (and even a small leakage not detected by automatics), the phase PE on one of the devices, a current begins to flow through the memory and its potential grows due to the resistance of the memory. If there are 2 or more independent chargers, this will lead to a potential difference between PE various electrical installations, which can create a risk of electric shock to people, as well as block (or even destroy) interface devices (Ethernet and others) that connect 2 parts of the system, grounded from independent chargers.

The right decision is to organize a potential equalization system.

All of the above also applies to artisanal groundings of the type “we dig a bucket in the garden and ground one device on it,” which are sometimes arranged in rural areas.

The flow of the operating current of the line through the local memory

Understanding the grounding device

Due to the misconception about the principle of operation of the local memory, one can often find the opinion that in the event of a break in the PEN conductor ( Protective Earth + Neutral protective and neutral conductor in one wire) on the supply line, the operating current of the zero-potential conductor can flow through the grounding devices of consumers located after the PEN conductor break. The most common way to "eliminate this danger" of this misconception is to create emergency modes of operation by installing a two-pole circuit breaker as an introductory knife switch.

Explanation of the cause of a common error

The fear of high currents flowing through the consumer's charger would only be justified if the soil between the consumer's charger and the charger of the transformer substation was made of metals with low resistance. Since, in practice, building grounds are connected to the transformer ground only by the main PEN conductor, in the event of its breakage, the resistance will increase sharply due to the absence of conductors parallel to the PEN conductor, thereby eliminating the possibility of high currents flowing through the local grounding device.

Since the resistance of the ground loop of the local charger is taken to calculate the parameters of the consumer's electrical installation (to reduce the likelihood of creating a dangerous step voltage on the consumer's territory, the minimum possible numerical value is usually required), the resistance of the soil between the transformer supplying the consumers and the consumer's local charger is not taken into account - the result of the resistance of the local The memory of an individual consumer is taken only for a single consumer, and not for the entire electrical network. In other words: since the exposed metal parts of a single consumer are not connected directly to the transformer (but only through the main ground bus), in the event of a break in the PEN conductor between the consumer’s charger and the transformer substation’s charger, a huge electrical resistance forms through the soil between them, which, according to the law Ohm does not allow large currents to flow through the memory of a single consumer.