Grounding grounding of electrical equipment. Grounding and grounding of electrical installations: functions, specifics, device. Legacy TN-C system

Protective grounding is called intentional electrical connection with earth or its equivalent of metal non-current-carrying parts that may become energized when shorted to the case and for other reasons.

Task protective earth- elimination of the danger of electric shock in case of touching the case and other current-carrying metal parts of the electrical installation that are energized. Protective grounding is used in three-phase networks With isolated neutral.

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

If the body of the electrical equipment is not grounded and is in contact with the phase, then touching such a body is equivalent to touching the phase. In this case, the current passing through a person (with low resistance of shoes, floor and wire insulation relative to the ground) can reach dangerous values.

If the case is grounded, then the amount of current passing through a person is safe for him. This is the purpose of grounding, and therefore it is called protective.

Zeroing is a deliberate electrical connection with zero protective conductor metal non-current-carrying parts that may be energized due to a short to the case and for other reasons.

The task of zeroing is to eliminate the danger of electric shock in case of touching the case and other non-current-carrying metal parts of the electrical installation that are energized due to a short to the case. This problem is solved by quickly disconnecting the damaged electrical installation from the network.

When zeroing, if it is reliably performed, any short circuit to the body turns into a single-phase short circuit(i.e. short circuit between phases and neutral wire). In this case, a current of such strength arises at which the protection (fuse or circuit breaker) is activated and automatic shutdown damaged installation from the network.

At the same time, zeroing (like grounding) does not protect a person from damage. electric shock with direct contact with current-carrying parts. Therefore, there is a need (in rooms that are especially dangerous in relation to electric shock) to use, in addition to zeroing, other protective measures, in particular, protective shutdown and potential equalization.

Protective grounding is an intentional electrical connection to the ground or its equivalent of metal non-current-carrying parts that may become energized due to a short to the case and for other reasons (inductive influence, potential removal, etc.). The principle of operation of protective grounding is to reduce the voltage between the housing that is energized and the ground to a safe value. This voltage is called the touch voltage U PR. This is achieved by reducing the potential of the grounded equipment, as well as by equalizing the potentials of the base on which the person stands and the grounded equipment, due to the appearance of potentials on the earth's surface when current drains into the ground.

Grounding conductors are connected to each other, as well as to grounding conductors and grounded structures, as a rule, by welding, and with the bodies of apparatuses, machines and other equipment - by welding or using bolts.

Zeroing of electrical installations is the deliberate connection of metal non-current-carrying parts of electrical installations, which may become energized due to insulation breakdown, with a zero protective conductor. When any phase is closed to the case, a short circuit is formed, characterized by a very large current, sufficient to “knock out” the fuses in the phase supply wires. Thus, the electrical installation is de-energized. Re-grounding of the neutral conductor is provided in case of a wire break in a section close to the neutral. Through this grounding, the current flows to the ground, from where it enters the neutral ground, through it into all phase wires, including those with broken insulation, then to the case. This creates a short circuit.

Question 7. Implementation of the achievement of the goals in the field of OSMS.

The goal is to improve the effectiveness of risk management in the field of labor protection.

The OSH objectives are the basis for the implementation of the OSH Policy and the development of the OSH management program.

OSH objectives are used as the basis for monitoring and evaluating the effectiveness of the OSH.

Upon achievement of the objectives in the field of labor protection, activities of the labor protection management programs in terms of reducing significant risks, a revision is made in the direction of reducing the levels of significant and other risks. At the same time, changes are to be made to the relevant tables “Goals in the field of labor protection, the program for managing labor protection to ensure the implementation of the Policy in the field of labor protection”.

Ticket number 12

Question 1. Obligations of the employer to remove the employee from work.

Obligations of the employer to remove the employee from work (Article 49 of the Labor Code of the Republic of Belarus):

At the request of authorized state bodies in cases provided for by law, the employer is obliged to remove the employee from work.

1) appeared at work in a state of alcoholic, narcotic or toxic intoxication, as well as in a state associated with an illness that prevents the performance of work. The refusal of the driver to pass the instrumental control of intoxication is the basis for removing him from work (paragraph 7 of the Instruction approved by the resolution of the Ministry of Transport and Communications of the Republic of Belarus and the Ministry Agriculture and food of the Republic of Belarus of 09.07.2013 N 25/28);

2) who has not been instructed, trained and tested knowledge on labor protection issues;

3) not using the means personal protection directly ensuring labor safety;

4) who has not passed a medical examination, an examination for being in a state of alcoholic, narcotic or toxic intoxication in cases and in the manner prescribed by law.

During the period of absence from work wage is not charged, except for the cases provided for by part five of Article 49 of the Labor Code of the Republic of Belarus.

When an employee who has not been instructed, trained and tested on labor protection issues, a medical examination or examination for being in a state of alcoholic, narcotic or toxic intoxication in cases and in the manner prescribed by law, through no fault of his own, is suspended from work payment for the entire period of suspension from work in accordance with the first part of Article 71 of this Code.

In accordance with Article 49 of the Labor Code of the Republic of Belarus, at the request of authorized state bodies in cases provided for by law, the employer is obliged to remove the employee from work.

In addition to the cases provided for by law, the employer is obliged not to allow to work (suspend from work) on the relevant day (shift) of the employee:

1) appeared at work in a state of alcoholic, narcotic or toxic intoxication;

2) who has not been instructed, tested knowledge on labor protection;

3) not using the required personal protective equipment when performing work that ensures labor safety;

4) who has not passed a medical examination in the cases and in the manner prescribed by law.

An employee who has committed the theft of the property of an employer, the employer has the right to suspend from work until the entry into force of a court verdict or a decision of the body, whose competence includes the imposition of an administrative penalty.

During the period of suspension from work, wages are not charged.

When an employee who has not been instructed, tested on labor protection or medical examination in cases and in the manner prescribed by law, through no fault of his own, is suspended from work, he is paid for the entire period of suspension from work not less than two-thirds of the tariff rate established for him ( salary).

Similar information.

Basic condition safe operation electrical installations is the choice correct scheme protection against accidental contact with high potential on metal parts not used for power transmission (cases, beds, etc.). To solve this problem, the requirements of the current standards (PUE, in particular) provide for the use of special protective devices called grounding devices - GD. They are arranged in close proximity to the protected structure and have the form shown in the figure below.

The process of arranging structures that protect structures and people from electric shock or lightning is commonly called grounding in electrical engineering. In order to have a complete and clear idea of what grounding is, it will be necessary to examine it distinctive features and principles of organization in more detail.

The essence of grounding

Grounding refers to the intentional connection of metal parts of electrical installations and other equipment, in this moment not under voltage, with elements of special devices called ground electrodes. The design of the latter usually consists of several steel pins driven into the ground or pieces of reinforcement welded together by strips of the same metal.

Complete with a set of flexible copper wires and thick strips (tires) grounding conductors form the so-called "grounding loop", to which the cases of all electrical appliances available at the facility and in need of protection are connected. Since the contour itself is partially or completely immersed in the ground and has almost perfect contact with it, its potential is normal conditions close to zero, which leads to the following conclusions:

On hit high voltage on the metal parts of a protected object or device, its value will immediately drop to a level that is safe for humans (photo below);

If a person or an animal accidentally touches the body of an emergency, but protected in this way, equipment, they will practically not suffer from high voltage;
In a situation where a sensitive device is installed in the supply line that responds to third-party leakage currents (RCD, for example), when a dangerous voltage appears, it will work and instantly disconnect this section from the power supply.

This is the essence of the grounding effect, which should not be confused with another protection technique often used in electrical engineering, called zeroing.

The concept of nulling

Each user inexperienced in electrical terms may have a question: how does grounding differ from zeroing, and also when is the latter used?

To understand the difference between grounding and zeroing, it will be necessary to consider the principle of equipment protection distribution substations, the essence of which is as follows:

Equipment of any power stations, including the step-down transformers installed on them, has a zero point or neutral;
In accordance with PUE requirements, this point is necessarily connected to the local charger, equipped directly on the territory of the substation;
Grounding is carried out in the form of a direct connection with the ground, as a result of which such a point is called dead-grounded;
The action of this grounding applies to all consumers connected to this electrical substation through an extensive power supply system.

Thus, to each consumer, along with phase wires the so-called "zero protective" core is brought in, already grounded tightly on the side of the substation (see photo).

Note! IN modern systems power supply (TN-C-S, for example), it is laid separately from the operating busbar N with a PE wire.

When zeroing the receiving equipment, its metal parts are deliberately connected not to the charger (as is done when grounding), but to the combined neutral wire that is part of the power supply system. In a TN-C-S system, they are connected to a separate PE conductor.

Zeroing provides a reduction in the threat of electric shock in case of accidental contact with open metal parts of the equipment, which, as a result of an accident, become energized. When questions like “what is the difference between zeroing and grounding” arise, you should always remember that the first guarantees automatic disconnection of the damaged line from the mains, and the second does not.

Differences between grounding and grounding

Often, users wonder if it is possible to do grounding instead of grounding, and how this will affect consumer safety. Answering all such questions, one should proceed from the definition given to this type of protection in previous section. It follows from it that functionally zeroing is more effective, since in a short period of time before the operation of station automation, it performs the same function as a conventional memory.

However, this does not mean that this species protection must be applied at all times and everywhere. The fact is that zeroing has a number of shortcomings, which are a consequence of the peculiarities of its organization. They appear as follows:

The neutral wire of power supply systems is long and is constantly used in active mode (as a conductor through which the operating current flows), as a result of which it can collapse over time;

Additional Information. This phenomenon in the technical literature, as well as among specialists, is most often referred to as “zero burnout” (see photo below).

Unlike grounding, during the arrangement of which there is no dependence on the phase of the protected line, when zeroing, certain conditions for connecting the protective conductor must be observed;
It is limited in its capabilities, since it can only be used in circuits with a tightly grounded neutral in TN-C-S, TN-C, TN-S networks (in the presence of N, PE, PEN conductors).

In lines where the connection is organized according to an isolated neutral scheme (in IT and TT systems), which are more suitable for industrial facilities by their purpose, it will not be able to work.

Also, these two types of deliberate protection differ in their scope, namely:

Zeroing is usually used in multi-storey buildings residential buildings where it is practically impossible to organize a full-fledged grounding;
Re-grounding is more commonly used on industrial enterprises where, according to safety regulations, increased requirements are imposed on the safety of personnel;
The same type of protection is most often used in everyday life (in country houses, in particular), where there are plenty of opportunities for arranging a protective circuit (see photo below).

It should be added that protective grounding and zeroing differ in one more an important factor. The fact is that in the first case, protection extends only to the area electrical circuit, on which in emergency mode (during the breakdown of insulation) due to the flow of current into the ground, the operating voltage has decreased. At the same time, the rest of the electricity supply system continues to function.

Unlike the action of the grounding effect, when grounding, this section of the power line is turned off completely.

So trying to answer the question, what is their difference, will not be entirely correct. It is much more correct to say that grounding and grounding of electrical installations should be used together. This combined use will provide more effective protection from electric shock.

Summing up their comparison, we note that the zeroing principle consists in the transformation emergency V single-phase short circuit, leading to the operation of the station protective automation. Grounding, on the one hand, is a decrease in the potential of a dangerous point (a decrease in the resistance of the ground electrode), and on the other, their equalization.

In this case, it consists in raising the potential of the support with a person standing on it to the voltage level on the grounded case.

Additional elements

Both in the case of grounding and zeroing for the implementation protective functions additional conductors must be used ( copper wires), providing a reliable connection with the charger or with a zero contact, respectively.

In the first case, this conductor is pulled from the protected point to the ground electrode contact and is made in the form of a copper braid. In a situation with zeroing, the same copper conductor it is laid in hidden places of premises and other buildings to the switch cabinet, where its end is fixed on the main ground bus (GZSH). A zero working conductor, which is part of the power cable supplying electricity, is also brought here.

Important! According to the requirements of the organization of grounding (see the PUE), the use of one bolt or terminal contact for fastening these two conductors is unacceptable, which is explained by the different modes of their operation.

At the end of the comparison of the two methods of protecting objects from electric shock, the following should be noted. Both of these methods (both zeroing and grounding), in fact, perform the same function, which consists in reducing the dangerous potential to an acceptable level. You zap some point of the equipment or protect it with the help of a memory, the effect will be about the same.

Video

Grounding the electrical installation- intentional electrical connection of its body with a grounding device.

Grounding electrical installations is of two types: protective earth And nulling, which have the same purpose - to protect a person
from electric shock if he touched the body of the electrical installation or its other parts that were energized.

Protective earth- intentional electrical connection of a part of an electrical installation with a grounding device in order to ensure electrical safety. Designed to protect a person from touching the body of the electrical installation or its other parts that are energized. The lower the resistance of the grounding device, the better. To take advantage of grounding, you need to buy sockets with a grounding contact.

In the event of an insulation breakdown between the phase and the body of the electrical installation, its body may be energized. If a person touched the case at that time, the current passing through the person is not dangerous, because its main part will flow through the protective ground, which has a very low resistance. Protective grounding consists of a grounding conductor and grounding conductors.

Eat two types of grounding – natural And artificial.

Natural grounding conductors are metal constructions buildings securely connected to the ground.

Used as artificial grounding steel pipes, rods or angle, not less than 2.5 m long, hammered into the ground and connected to each other with steel strips or welded wire. As grounding conductors connecting the ground electrode with grounding devices, steel or copper tires are usually used, which are either welded to the machine bodies or connected to them with bolts. Protective grounding is subject to metal cases electrical machines, transformers, shields, cabinets.

Protective grounding significantly reduces the voltage that a person can get under. This is due to the fact that the ground conductors, the ground electrode itself and the ground have some resistance. If the insulation is damaged, the fault current flows through the body of the electrical installation, the ground electrode and further along the ground to the neutral of the transformer, causing a voltage drop across their resistance, which, although less than 220 V, can be felt by a person. To reduce this voltage, it is necessary to take measures to reduce the resistance of the grounding conductor relative to the ground, for example, to increase the number of artificial grounding conductors.

Zeroing- deliberate electrical connection of parts of an electrical installation that are not normally energized with a dull earthed neutral with neutral wire. This leads to the fact that the short circuit of any of the phases on the body of the electrical installation turns into a short circuit of this phase with a neutral wire. The current in this case is much greater than when using a protective earth. Quick and complete shutdown of damaged equipment is the main purpose of zeroing.

Distinguish zero working conductor And zero protective conductor.

The zero working conductor is used to power electrical installations and has the same insulation as other wires and a sufficient cross section for the passage of the working current.

Zero protective conductor is used to create a short-term short-circuit current for protection operation and quick disconnection
damaged electrical installation from the mains. As a neutral protective wire, steel pipes of electrical wiring and neutral wires without fuses and switches.

Grounding system symbols

Grounding systems differ in connection schemes and the number of zero working and protective conductors.

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 in the designation of the grounding system 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 the 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 method of constructing the zero protective and zero working conductors:
C - the functions of the zero protective and zero working conductors are provided by one common PEN conductor.
S - functions of zero protective PE and zero working N conductors are provided by separate conductors.

Basic grounding systems

The TN-C system includes three-phase four-wire (three phase conductors and a PEN-conductor that combines the functions of zero working and zero protective conductors) and single-phase two-wire (phase and zero working conductors) networks of old buildings. This system is simple and cheap, but it does not provide the necessary level of electrical safety.

Currently, the use of the TN-C system on newly built and reconstructed facilities is not allowed. When operating the TN-C system in
an old building intended to house computer equipment and telecommunications, it is necessary to ensure the transition from the TN-C system to the TN-S (TN-C-S) system.

The TN-C-S system is typical for reconstructed networks in which the zero working and protective conductors are combined only in part of the circuit, during input device electrical installations (for example, an introductory apartment panel). In the input device of the electrical installation, the combined zero protective and working conductor PEN is divided into a neutral protective conductor PE and a neutral working conductor N. In this case, the neutral protective conductor PE is connected to all open conductive parts of the electrical installation. The TN-C-S system is promising for our country, it allows to provide high level electrical safety at a relatively low cost.

In the TN-S system, the zero working and zero protective conductors are laid separately. A five-wire cable comes from the substation. All open conductive parts of the electrical installation are connected by a separate neutral protective conductor PE. Such a circuit eliminates reverse currents in the PE conductor, which reduces the risk of electromagnetic interference. good option to minimize interference is an attached transformer substation(TP), which allows to ensure the minimum length of the conductor from the input of power supply cables to the main grounding clamp. TN-S system in the presence of an attached substation, it does not require re-grounding, since this substation has a main grounding conductor. This system is widespread in Europe.

4. TT grounding system

In the TT system, the transformer substation has a direct connection of current-carrying parts to 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 the transformer substation.

5. IT grounding system

In an IT system, the neutral of the power supply is isolated from earth, or earthed through high impedance appliances or devices, and exposed conductive parts are earthed. Leakage current to chassis or ground will be low and will not affect the operating conditions of the connected equipment. Such a system is used, as a rule, in electrical installations of buildings, which are subject to increased safety requirements.

Loop grounding scheme

1. Grounding
2. Ground conductors
3. Grounded equipment
4. Industrial building.

An example of a house grounding scheme

1. Water heater
2. Lightning protection grounding
3. Metal pipes
plumbing, sewerage, gas
4. Main ground bus

5. Natural grounding conductor (reinforcement of the foundation of the building)

Measures to protect against electric shock

Used to protect people from electric shock protective equipment- rubber gloves, tools with insulated handles,
rubber boots, rubber mats, warning posters.

Wire insulation monitoring

To prevent accidents from electric shock, it is necessary to control the condition of the insulation of the wires of electrical installations. The condition of the wire insulation is checked in new installations, after reconstruction, modernization, a long break in work.
Preventive control of wire insulation is carried out at least 1 time in 3 years. The insulation resistance of wires is measured with megohmmeters on Rated voltage 1000 V in the areas with the fuse-links removed and with the current collectors switched off between each phase wire and neutral working wire and between every two wires. The insulation resistance must be at least 0.5 Mohm.

The concept of step voltage. touch voltage.

In any electrical networks a person in the zone of current spreading may be under step voltage and touch voltage.

In accordance with GOST 12.1.009 "SSBT. Electrical safety. Terms and definitions" (hereinafter - GOST 12.1.009) step voltage(step voltage) is the voltage between two points of the current circuit, located one from the other at a step distance (0.8 m) and on which a person is simultaneously standing.

largest electric potential will be at the point of contact of the conductor with the ground. As you move away from this place, the potential of the soil surface decreases, since the cross section of the conductor (soil) increases in proportion to the square of the radius, and at a distance of approximately 20 m, it can be taken equal to zero. The danger of step voltage increases if the person who has been exposed to it falls: the step voltage increases, since the current no longer passes through the legs, but through the entire body of a person.

touch voltage called the voltage between two points of the current circuit, which are simultaneously touched by a person (GOST 12.1.009). The danger of such a touch is estimated by the value of the current passing through the human body, or by the voltage of the touch, and depends on a number of factors: circuits for closing the current circuit through the human body, network voltage, circuits of the network itself, its neutral mode (i.e. grounded or isolated neutral) , the degree of isolation of current-carrying parts from the ground, as well as the value of the capacitance of current-carrying parts relative to the ground, etc.

Protective grounding is an intentional electrical connection to the ground or its equivalent of metal non-current-carrying parts that may become energized when shorted to the case and for other reasons.

The task of protective grounding is to eliminate the danger of electric shock in case of touching the case and other current-carrying metal parts of the electrical installation that are energized. Protective grounding is used in three-phase networks with isolated neutral.

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

If the case is grounded, then the amount of current passing through a person is safe for him. This is the purpose of grounding, and therefore it is called protective.

Zeroing is a deliberate electrical connection with a neutral protective conductor of metal non-current-carrying parts that may be energized due to a short to the case and for other reasons.

When zeroing, if it is reliably performed, any short circuit to the body turns into a single-phase short circuit (i.e., a short circuit between the phases and the neutral wire).

In this case, a current of such strength arises at which the protection (fuse or circuit breaker) is activated and the damaged installation is automatically disconnected from the network.

At the same time, grounding (as well as grounding) does not protect a person from electric shock by direct contact with live parts. Therefore, there is a need (in rooms that are especially dangerous in relation to electric shock) to use, in addition to zeroing, other protective measures, in particular, protective shutdown and equalization of potential.

When accepting a grounding device for operation, the acceptance committee is presented with: executive drawings and diagrams of grounding devices, acts on hidden work, acts of checking openly laid grounding conductors, protocols for measuring resistance. The resistance to the flow of grounding conductors is checked special devices: M–416 (M–08).

The grounding device must have a passport.

Periodically, grounding must be inspected and tested;

At least once a year during periods of the lowest soil conductivity in summer or winter - measure the resistance of the grounding device. The results are documented and recorded in the passport.

Classification of premises according to the danger of electric shock.

The requirements for electrical equipment largely depend on the room in which it is installed.

On the danger of electric shock to people industrial premises subdivided:

1. Particularly dangerous - have high humidity(approximately 100%) or a reactive medium, or both.

2. Increased danger - With relative humidity exceeding 75% for a long time or there are conductive floors, conductive dust, air temperature exceeds +35°C for a long time, etc.

3. Premises without increased danger - none of the above factors. Electrical installations outdoors are equated to especially dangerous.

Requirements for personnel serving electrical installations:

Persons at least 18 years of age who have passed a medical examination and special electrical training are allowed. They must have a good knowledge of electrical engineering, electrical equipment, circuits and features of the devices being serviced; must have a clear understanding of the possible dangers, know and skillfully apply the electrical safety rule, be able to provide first aid to the victim.

The level of required knowledge is determined by the electrical safety qualification group. The higher the qualification group, the more requirements are placed on the employee. There are 5 installed groups.

Periodic checks of personnel are carried out:

1 time per year - for personnel directly servicing existing electrical installations and for employees who issue orders and organize these works;

1 time in 3 years - for engineers and technicians (engineering and technical workers) who do not belong to the previous group, labor protection engineers admitted to inspect electrical installations.