When organizing a household electrical network, it is necessary to take into account the electrical safety class of each room in a house or apartment. Those who believe that the classification of premises according to the danger of damage electric shock applicable only to production facilities, are deeply mistaken. In modern houses and apartments there are rooms belonging to the category of increased danger, which should be taken into account when designing and installing electrical wiring.

What conditions affect electrical safety?

There are many factors that increase the risk of electric shock. First of all, it is water. AT pure form it is an insulator, but salts and other impurities dissolved in it conduct electricity perfectly. Since distilled water does not exist in nature, this liquid should be considered as conductive. Accordingly, a high concentration of water vapor, leading to the formation of condensate, increases the likelihood of breakdown on the body of electrical equipment, creates a threat and increases the risk of direct or indirect contact with current-carrying elements.

No less dangerous is the high concentration of tiny conductive particles in the air. Such dust settles on the current-carrying elements of the equipment, forming conductor paths through which electricity can pass to various metal structures. As a result, there is a direct threat to the life of maintenance personnel, not to mention equipment failure and more serious consequences.

Dust also interferes with heat dissipation by covering electrical equipment cases or settling on ventilation grilles. This leads to a violation of the temperature regime of operation, which can cause a serious accident.

Speaking of excessive heat, this is also a destructive factor affecting electrical safety. High temperature contributes to early wear of current-carrying elements and destroys their insulating coating. What this can lead to is described above.

Active chemicals are also hazards. At a certain concentration in the air, they practically “eat up”, destroy the contacts of the switching equipment and form conductive chemical compounds.

To reduce the impact of destructive factors, it is necessary to apply certain measures described in the electrical safety requirements. To this end, a system for classifying premises according to the degree of danger has been adopted, with detailed description regulatory requirements for each group.

Classification

No matter how reliable the insulating coating is, it cannot last forever, especially when the technological cycle requires difficult conditions. Other factors can also pose a threat, such as metal flooring in a production facility or the location of electrical equipment near grounded metal structures. This, if touched indirectly, can cause electric shock.

To improve the efficiency of electrical safety, a system for classifying premises according to the degree of danger was developed. In accordance with current regulations (see PUE, clause 1.1.13), all types of premises (household, industrial, administrative, etc.) are divided into three groups. Each of them will be discussed in detail below.

First class - "premises without increased danger"

This group includes any type of premises meeting the following conditions:

• Low humidity, usually not exceeding 60.0%.
• Air conditioning systems are allowed, including ventilation and heating.
• The floor covering must be made only of dielectric materials. That is, earthen, reinforced concrete and metal floors are excluded.
• Air temperature up to 30.0°С.
• There is no emission of process dust.
• There are no chemically active substances in the air.

That is, in the premises of this group, the presence of any destructive factors affecting the decrease in the level of electrical safety is unacceptable. As an example, we can cite premises in residential, office, retail and administrative facilities.

If the above conditions are met, production facilities, for example, “clean” shops where electronic components are manufactured, can also be included in this category. At such facilities, almost sterile conditions are created, a constant air temperature and a given level of humidity are maintained.

Second class - "Premises with increased danger"

Any room can be included in this group if at least one of the hazard factors inherent in this class is present. Let's list them:

• Increased moisture content in the air (over 75.0%). Details of the humidity standards can be found in the PUE (see clause 1.1.8).
• The presence of a large concentration of conductive dust generated during the process.
• The floor covering conducts electricity (reinforced concrete, metal, earth, etc.).
• The air temperature does not fall below 35.0°C. Permissible norms temperature conditions for various classes of premises are given in the PUE (see clause 1.1.10).
• There is a risk of electric shock if there is indirect contact with current-carrying elements. For example, as a result of an insulation breakdown, a dangerous voltage is present on the machine casing, and a grounded metal structure (column, beam, pipes, etc.) is located nearby. If the structure and the casing are touched at the same time, the worker will be under deadly voltage.

Third class - "Especially dangerous premises"

There are three conditions for any of which a room can be classified as a special hazard category, list them:

1. High moisture concentration, i.e. relative humidity reading close to 100.0%.
2. Exceeding the permissible limits concentration in the air of chemically active compounds that can harm electrical equipment (destroy electrical insulation, contacts, current-carrying wires, etc.).
3. Indoors more than one factor from the list of conditions for the second category of danger. For example, high level temperature (from 35.0°C) and humidity (75.0% or more).

As a striking example of a production facility that meets all three of the above conditions, galvanizing shops can be cited.

It should be noted that, according to electrical safety standards, open and covered sites are included in the third category. Accordingly, this group includes any types of open switchgears(ORU).

What is the danger?

First of all, this is the risk of electric shock, for example, high humidity leads to a shift in the dew point, as a result, a water concentrate can form even at normal temperatures. Actually, for this reason, in any house or apartment, the bathroom belongs to the 2nd category according to the norms of the accepted classification.

At a temperature of more than 35.0 ° C, the service life of the insulating coating of wires and other current-carrying elements is reduced. As a result, a “breakdown” may occur long before the end of the warranty period specified by the cable manufacturer.

Dust can cause a short circuit or cause the equipment to overheat. Chemically active compounds also introduce destructive actions, destroying insulation and current-carrying elements.

To ensure the proper level of electrical safety in the premises of the 2nd and 3rd class, it is necessary to take a number of special measures, and almost all of them must be taken into account at the design stage of the facility.

Increasing the level of electrical safety

Consider the measures that can be applied to provide the necessary level of protection against the harmful effects of electric current:

• Most reliable way ensure electrical safety in wet rooms - reduce the operating voltage of the power supply (including lighting). For this, a step-down transformer is used, which, in addition to its main functions, also provides galvanic isolation. For premises of the 2nd and 3rd class, the PUE prescribes a voltage in the network of 12.0 V and 42.0 V, respectively.

In everyday life, it does not make sense to lower the voltage in the electric points of the bathroom, due to the lack of widely available electrical equipment operating from 42.0 V. Therefore, it is necessary to minimize the amount of equipment, and install the electric points with a degree of protection of at least IP44. In addition, lines to the boiler, washing machine or other equipment located in the bathroom must be protected by RCDs or diffusers.

• The problem of dustiness, elevated temperature and concentration of chemically active elements, in some cases, can be solved by installing appropriate ventilation equipment.
• To reduce the risk of electric shock due to indirect or direct contact, the equipment is connected to protective earth, and other technical measures are taken (installation of fences, warning signs, etc.).

The listed measures will be incomplete if we do not mention the mandatory electrical safety briefing conducted at regular intervals. The effectiveness of this event has been repeatedly proven by industrial practice.

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Where work is connected with electricity, there is always the possibility of electric shock to a person. Impact of adverse conditions external environment aggravated by the fact that the human body is able to provide little resistance. And if there is high humidity in the room, then the probability of electric shock increases, since human sweat conducts it very well. There is a classification of premises according to the danger GOST provides for three classes.

Classification of premises without increased danger

In such rooms and air humidity, there is no dust, the floors are made of materials that do not conduct current (usually wood), there are no grounded objects or their number is minimized. These rooms allow you to use with a voltage of 220 volts. Classification of premises according to the danger of electric shock includes:

• rooms for the work of administrative and managerial personnel;
• computer technology centers;
• auxiliary, instrumental and control rooms.

Classification of premises with increased danger

These spaces are characterized by:

• relatively high air humidity, exceeding 75%;
• temperature with a constant or periodic mark on the thermometer of 35 degrees;
• conductive dust that covers wires and internal surfaces of electrical equipment;
• conductive floors. They are made of materials such as metal, brick, reinforced concrete, or simply earth.

The room belongs to the category of increased danger if at least one of these characteristics is present. The classification of premises according to the danger of electric shock of this class applies to the production premises of enterprises associated with vehicles, zones by maintenance and repair, thermal, welding departments.

Classification of premises of special danger

They differ:

• excessive which reaches 100%, due to which condensation forms in the room;
• the presence in the room of chemical aerosols that conduct current, as well as vapors, liquids and gases, which gradually destroy the insulation and conductive parts of electrical equipment.

A room affected by mold is also considered especially dangerous, since it, along with chemical gases, can also destroy the insulating layer. It is unacceptable for moisture to penetrate the building from the outside. A constant downpour will make it especially wet, and, therefore, extremely dangerous. A room that is characterized by two or more conditions at the same time is also considered especially dangerous. This classification of premises according to the danger of electric shock refers to:

• warehouses in which fuels and lubricants are stored and;
• battery and painting departments;
• washing and steaming chambers.

On the territory with the placement of outdoor electrical installations classification of premises according to the danger of electric shock. contain the basic requirements that electrical installations must comply with. The area may or may not be fenced. It is necessary that the electrical equipment has reinforced insulation.

In cases of electrical shock to the object, it is necessary to influence the flame (when ignited) by any fire extinguishing means. This is ordinary water. But here, too, there are drawbacks. Since water has a high electrical conductivity, it should not be used in case of ignition of electrical installations with high voltage. In the case of extinguishing oil products, the situation is complicated by the fact that they continue to burn on its surface. In these cases, chemical foam and powder formulations are used.

In order to prevent electrocution, it is always better to minimize the risk, namely:

1. Use protective barriers around electrically hazardous areas. Such protection will help to avoid close contact with live objects and, as a result, protect against electric shock.
2. The use of an interlock will help to avoid an accident if the current is restricted due to equipment failure.
3. To avoid emergencies, use portable ground electrodes, especially if work is carried out in open areas where there is direct contact with the ground. The grounding switch will direct electricity, in case of a situation overvoltage, into the ground.
4. Comply with technical safety measures using protective insulation, etc.).

In the regulatory documents, a special group highlights the work carried out in adverse conditions. For example, in boilers, apparatuses, vessels made of metal, where the operator's ability to move and exit from an enclosed space is limited. In this regard, there is a classification of premises according to the danger of electric shock. Therefore, the requirements for conditions that ensure safety are higher than in rooms with a special danger.

The degree of safety of maintenance of electrical installations largely depends on the operating conditions and the nature of the environment of the premises in which the electrical equipment is installed. Moisture, dust, caustic fumes, gases, high temperatures have a destructive effect on the insulation of electrical installations, thereby significantly worsening safety conditions.

Premises are classified according to the highest explosion hazard class of the installations located in them. Aggressive, damp, dusty and similar environments not only worsen the working conditions of electrical equipment, but also increase the danger of electrical installations for people serving them. Therefore, in the Electrical Installation Rules (PUE), premises Depending on the possibility of electric shock, people are divided into three groups:

• with increased risk;
• especially dangerous;
• without increased risk.

Premises without increased danger- these are premises in which there are no conditions that create an "increased danger" or "special danger". Non-hazardous areas include dry, dust-free rooms with normal air temperature, insulating (for example, wooden) floors, with no or very few earthed objects. An example of non-hazardous premises are ordinary living rooms, laboratories, as well as some industrial premises, including assembly shops of watch and instrument factories, located in dry, dust-free rooms with insulating floors and normal temperature.

Depending on the type of technological activity in premises of various categories and the possibility of electric shock to people, the nature of the design of the electrical equipment used for this environment, the types and methods of performing electrical networks are determined.

Premises with increased danger, characterized by the presence in them of one of the following conditions that create an increased danger:

• a) dampness (relative air humidity exceeds 75% for a long time) or conductive dust (according to production conditions, process dust is released in such an amount that it can settle on wires, penetrate inside machines, devices, etc.);
• b) conductive floors (metal, earthen, reinforced concrete, brick, etc.);
• c) high temperature (temperature exceeds constantly or periodically (more than 1 day) +35 °C);
• d) the possibility of a person simultaneously touching the metal structures of buildings connected to the ground, technological devices, mechanisms, etc., on the one hand, and to the metal cases of electrical equipment, on the other.

An example of high-risk areas are stairwells of various buildings with conductive floors, woodworking workshops, even if they are located in dry, heated buildings with insulating floors, since there is always the possibility of touching the motor housing and the machine at the same time, etc.

Majority industrial premises refer to high risk areas, i.e. they are characterized by the presence of dampness (relative humidity exceeds 75% for a long time) or conductive dust, conductive floors (metal, earthen, reinforced concrete, brick), high temperature (exceeding 30 ° C for a long time), as well as the possibility of simultaneous human touches to the metal structures of buildings connected to the ground, technological devices, mechanisms, on the one hand, and to the metal cases of electrical equipment, on the other.

Particularly dangerous premises, characterized by the presence of one of the following conditions that create a particular hazard:

• a) special dampness (relative air humidity is close to 100% - the ceiling, walls, floor and objects in the room are covered with moisture);
• b) chemically active or organic environment (aggressive vapors, gases, liquids are constantly or for a long time, deposits or mold are formed that destroy the insulation and current-carrying parts of electrical equipment);
• c) simultaneously two or more conditions of increased danger.

Particularly dangerous premises are most of the industrial premises, including all workshops of machine-building and metallurgical plants, power plants and chemical enterprises, water pumping stations, battery rooms, electroplating shops, etc.

Also read with this:

With increased risk:

dampness (more than 75%)

conductive dust

conductive floors

heat

the possibility of simultaneous contact with the metal structures of the building that have a connection to the ground, technological apparatus on the one hand and to the metal cases of electrical equipment on the other.

Particularly dangerous premises:

special dampness

chemically active or organic medium

2 or more high-risk conditions at the same time

Premises without increased danger - no conditions of increased danger

Damp rooms - relative humidity above 75%

Particularly damp rooms - relative humidity close to 100%

Hot rooms - the temperature constantly or intermittently (more than a day) exceeds 35 ° C

Dusty rooms - according to the conditions of production, technological dust is released.

A room with a chemically active or organic environment - constantly or for a long time contains aggressive vapors, gases, liquids, deposits, mold are formed.

Ensuring electrical safety, protective grounding, grounding, shutdown. Protective ground.

Intentional connection to earth and other structural, metallic parts of electrical equipment that are not normally energized, but may become energized by accidental connection to current-carrying parts. The task of protective grounding is to eliminate the danger of human shock in case of touching the housing that is energized.

Scope of protective grounding three-phase power supply networks up to 1000 V. with isolated center.

The principle of operation of protective grounding is to relieve the voltage between the housing that is energized and to a safe value. So the difference at protective earth and without current will be about 150 times.

Grounding devices this is a set of ground electrode - metal conductors. Grounding conductors are artificial and natural. Grounding conductors are usually made of sheet steel.

Equipment to be grounded is metal non-current-carrying metal parts of electrical equipment, while in rooms with increased danger or especially dangerous grounding installations above 12 volts AC or 110 volts DC.

Zeroing

Zeroing called connection to the repeatedly grounded neutral wire of the power supply network of cases and other metal parts of electrical equipment that are not normally energized.

The task of grounding is the same as that of protective grounding.

Zeroing principle --transformation of breakdown to the body into a single-phase short circuit (i.e., a short circuit between the phase and the neutral wire) in order to cause a large current that can ensure the operation of the protection, i.e. disconnect the units from the power supply. Such protection are: fuses, automatic devices.

Zeroing scope: three-phase four-wire networks up to 1000 V. with a solidly grounded neutral.

protective equipment

Protective equipment is divided into three groups: insulating, enclosing, protective.

insulating - provide isolation of a person from current-carrying parts, as well as from the ground. insulating protective equipment divided into basic and additional.

Basic insulating means- capable of withstanding operating voltages for a long time (up to 1000 V - rubber gloves, tools with insulated handles).

Additional insulating means- up to 1000 in. dielectric galoshes, rugs.

Enclosing means - temporary fencing - shields, portable grounding.

Safety - protective glasses, gas masks, safety belts.

Grounding and Electrical Safety Measures

Terminology

Solidly grounded neutral- transformer or generator neutral connected directly to the earthing device.

Isolated neutral- the neutral of the transformer or generator, not connected to the grounding device or connected to it through a high resistance.

neutral - common point windings (elements) of equipment connected in a star.

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

As natural grounding can be used:

metal and reinforced concrete structures of buildings and structures in contact with the ground

metal water pipes laid in the ground

rail tracks of main non-electrified railways in the presence of a deliberate arrangement of jumpers between the rails

metal structures or structures located in the ground

metal sheaths of armored cables laid in the ground.

Artificial ground electrodes can be made of black or galvanized steel or copper. Artificial ground electrodes should not be colored.

Protective earth- grounding performed for electrical safety purposes.

Protective zeroing

In networks with a dead-earthed neutral, protective zeroing is most effective.

Protective zeroing- intentional connection of open conductive parts with dead-earthed neutral in networks three-phase current or with a dead-earthed output of the source in networks single-phase current performed for electrical safety purposes.

The principle of operation - the transformation of a short circuit to the body into a single-phase short circuit in order to call high current short circuit, capable of ensuring the operation of current protection and thereby quickly automatically disconnect the damaged installation from the mains.

exposed conductive part- this is a part of an electrical installation accessible to touch that is not normally energized, but which may become energized if the main insulation is damaged.

direct touch- contact with live parts

indirect touch- contact with open conductive parts that become energized when the insulation is damaged.